identification and control of€¦ · remain the same genetically. during sexual reproduction,...

Vladimer Baramidze, Andro Khetereli, Mosbah Kushad

Identification and Control of Major Diseases and Insect Pests of

Vegetables and Melons in Georgia

© Baramidze, Khetereli, Kushad and MEAS This work is licensed under a Creative Commons Attribution 3.0 Unported License.Users are free:• Toshare—tocopy,distributeandtransmitthework.• Toremix—toadaptthework.Under the following conditions:• Attribution—usersmustattributetheworktotheauthorsbutnotinanywaythatsuggeststhattheauthorsendorsethe user or the user’s use of the work.

Identification and Control of

Major Diseases and Insect Pests of

Vegetables and Melons in Georgia

Tbilisi2015

Vladimer Baramidze, Andro Khetereli, Mosbah Kushad

ThispublicationisfundedbytheUSAIDundertheSEASProject(StrengtheningExtensionandAdvisoryServicesinGeorgia). TheviewsexpressedinthispublicationarethoseoftheauthorsanddonotnecessarilyrepresentthoseofUSAID.

Editors: Mike Ellis, Ben Mueller, Roger Williams

Publishing Coordinators: Anna Milashvili, Lisa Basishvili

Proofreaders: TatiaGogaladze,EkaterineShubladze

Designer: NataliaGlonti

ISBN:978-9941-0-8065-4

©AgriculturalUniversityofGeorgia2015

Horticultural crops are a significant and expanding component of agriculture inGeorgia.Open-fieldhorticulturalcropsproduction in2015hasbeenestimatedtobe48,000hectare(ha),andabout200haforyear-roundgreenhousesvegetableproduc-tion.AccordingtotheNationalStatisticsDepartmentofGeorgia, the2014vegetableproductioncoveredlessthan50%ofthepercapitademandofabout93kg.

Theshortage invegetableproduction isoffsetby importedproductsfromneigh-boringcountrieslikeTurkeyandIranandfromothersourcesoverseas.Despitesignifi-canteffortsfromtheMinistryofAgriculturetoincreaseproductionoverthepastseveralyears,theaverageyieldperhectareofimportanthorticulturalcropshasnotincreasedsignificantly.Thelowyieldispartiallyduetothefactthatmostvegetableproductionisdonebysmallfarmerswhohavedifficultyaccessinginformationforsuccessfullycon-trollingpests,forapplyingproperfertilizers,andforobtaininghighqualityseedsandother planting material, like vegetable varieties that are disease resistant or have other favorable horticultural characteristics, that will help them cover the high demand for vegetables in thecountry.Currently, thereareapproximately43,430smallvegetablefarmersinGeorgia.Mostofthesesmallfarmersarehighlymotivatedtoadoptinnovati-veproductiontechniquestohelpincreasetheproductionontheirfarms.

ThisbookprovidesinformationtohelpGeorgianvegetablefarmersrecognizeim-portantplantdiseasesandinsectpestsaffectingtheircropsandtodevelopandemploystrategies for their control. The first chapter is an introduction highlighting the general principlesofplantpathologyforvegetablesandmelons.Thechapteralsodiscussesin-tegrated concepts of disease management, which will be helpful in implementing co-rrect preventive measures to reduce the risk from diseases. The second part of the book dealswithdiseases(causedprimarilybybacteria,fungiandviruses)affectingspecificvegetables such as tomatoes, cucumbers, cabbages, and other important vegetable cropsandmelonsgrowninGeorgia.VegetablesandMelonscoveredinthebookletareorderedaccordingtotheGeorgiaalphabet.Thefieldguideprovidesphotosandcharts,whichwillhelpusersidentifydiseasesbysymptoms.Thefieldguidealsocontainsdi-seasemanagementstrategies,whichweredevelopedto includetheuseofcurrentlyregistereddiseasecontrolchemicals(primarilyfungicides)thathavebeenapprovedbytheGeorgiaMinistryofAgriculture.

PublicationofthisbookletisfundedbyUSAIDaspartoftheStrengtheningExten-sionAdvisoryServicesinGeorgia(SEAS)Project.TheauthorsofthefieldguideareProf.VladimerBaramidze,Mr.AndroKhetereli,andDr.MosbahKushad.Editors includeDr.MikeEllis,Mr.BenMueller,andDr.RogerWilliams.SpecialthanksaregiventoDr.RolandSmith,Ms.LisaBasishvili,LucasLeanne,BentsenMolly,andallmembersoftheproject.

Vladimer BaramidzeProfessor,AgriculturalUniversityofGeorgia

Preface

EGGPlant ......................................................................................................................... 29

Potato ............................................................................................................................. 35

CuCuMbEr ........................................................................................................................ 48

CabbaGE ........................................................................................................................... 62

toMato ............................................................................................................................. 75

Carrot ............................................................................................................................. 94

PEPPEr ........................................................................................................................... 105

tablE bEEt .................................................................................................................... 117

onIon, GarlIC................................................................................................................ 126

WatErMElon ................................................................................................................. 138

MElon ............................................................................................................................. 145

InsECts .......................................................................................................................... 152

Glossary ....................................................................................................................... 191

lItEraturE CItED........................................................................................................ 195

PICturEs CItED ............................................................................................................ 197

IntroDuCtIon ....................................................................................................................9

content

8 Identification and Control of Major Diseases and Insect Pests of Vegetables and Melons in Georgia

9

Chapter 1

PLANTDISEASEPlantdiseasesrepresentacomplexproblem,thesameasdiseasesofhumansand

animals.Damagecausedbydiseasesismanifestedbothinradicaldecreaseofproduc-tivityandlossofqualityofcommodityvalueofproduce.Itiscurrentlycalculatedthatpests,diseases,weeds,etc.destroyhalfoftheproductsgrownintheworld.Alongwiththeincreaseofhumanpopulationnumbers,demandforfoodproductsisgrowingdaily,which gives greater significance to knowledge and prevention of plant diseases.

Healthyplantscanbegrownonlyifweunderstandwhatthecausalagentsofplantdiseasesare.Itisalsoimportanttoknowhowtheyspreadandhowwecanlimittheirspreadinordertoeffectivelymanagethem.Plantdiseasescangenerallybedividedintotwolargegroups.Thereareabioticdiseases,whicharenotcausedbylivingorganisms.Theyarecausedmostlybyimproperenvironmentalconditionssuchasexcessiveheatorcold,excessivesoilmoistureandmineraldeficienciesinsoil.Theycanalsobecausedbythemisapplicationofpesticides,especiallyherbicides.Bioticdiseasesarecausedbylivingparasiticorganismssuchasfungi,bacteria,andnematodes.Inorderforinfectiontodevelopinaplant,existenceofthefollowingthreemainfactorsisrequired:asuscep-tible host plant; environmental conditions conducive to disease development, and the pathogen(Fig1.0).

Pathogentypeandinteractionwiththehostplantareofgreat importancefordi-seasedevelopment.Itisalsonecessarytoknowthecontributingandhinderingfactorsofthedisease,aswellasthoseenvironmentalconditions(soil,moisture,humidity,me-teorologicalconditions,etc.)inwhichtheplanthastogrowanddevelop.Whenthesefactorsaffecttheplantnegatively,theplantweakensandbecomessusceptibletodisea-ses.Ifweunderstandalloftheseconditions,wewillbeabletodevelopeffectivediseasemanagement programs for the disease.

Introduction

Pathogen

Susceptible Plant

NoDisease

DiseaseDevelops

Environment

P

P

SP

SP

E

EFigure 1.0 Disease development triangle. (P) Pathogen (E) Environment (SP) Susceptible Plant. In order for the disease to develop, the combination of these three factors is necessary. When one of the factors is lacking, disease does not develop.


Introduction

BIOTICFACTORS(PLANTPATHOGENS) FungiandFungal-LikeOrganisms

Morphology:Mostfungihaveavegetativebodycomposedoffilaments,whicharecalledmycelia. Individualbranchesofmyceliumarecalledhyphae,whicharemostlythinandthread-like.Thelengthofmyceliavariesfromseveralmicronstoseveralmetersindifferentspeciesoffungi.Somefungicontainoneortwonucleiineachcell.Othersconsist of multiple nuclei, which can be separated by a cross wall (septa). Myceliagrowat the endsof hyphal tips.Many fungiproduce specialized structures for longterm survival in soil such as sclerotia and chlamydospores.They also producemanyspecializedstructuresforuseinasexualandsexualreproduction(Fig1.1)

Reproduction: Fungireproduceintwomainways:asexualandsexualreproduction.Fungiwhich are capableof both sexual and asexual reproduction are calledperfectfungi. Fungi that are capable of only asexual reproduction are called imperfectfungi. Asexual reproduction can be vegetative or occur through the production ofspores. Vegetative reproduction takes place by means of the fungus mycelium orthrough the formation of other specialized structures such as rhizomorphs, sclerotia, chlamydospores,andconidia. Inasexual reproduction, there isnomeiosis (reductiondivision)andthereisnosexualrecombinationofgeneticmaterial.Thefungalstructuresremainthesamegenetically.Duringsexualreproduction,meiosis(reductiondivision)andsexualrecombinationofgeneticmaterialoccurs.Thisresultsintheproductionofsporeswhicharegeneticallydifferent.Differenttypesoffungiproducedifferenttypesofsexualsporesinspecializedstructures.

Ecology: Some types of plant pathogenic fungi known as non-obligate parasitesspendpartoftheir lifecycle inthe livinghostorganismandpartof itonplantparts(debris)existinginthesoil.Someothertypesoffungiareknownasobligateparasitesorbiotrophs,which cangrowand reproduceonlyon livinghostplantsduring theirwholelifecycle.Someoftheseobligateparasitesincludethefungithatcausepowderymildews,downymildewsandrustdiseases.Basedonecology,fungiaredividedintothefollowing groups.

• Non-obligate-Most plant pathogenic fungi and bacteria can live on either living or deadhostsandonvariousnutrientmedia.Thesearecallednon-obligateparasites.Non-obligate parasites can be facultative saprophytes or facultative parasites,dependingonwhethertheyareparasitesorsaprophytes.

• Facultative saprophytes - can grow on hosts as parasites, but can also continuegrowing and reproducing on the host’s dead tissue. These fungi aremainly soilpathogens, which have a wide range of host organisms and can remain in the soil formanyyears.

• Facultative parasites – areorganismsthatareusuallyparasiticbutmayliveassapro-phytesinthesoils.

• Biotrophs – spend theirwhole life cycle on living host organisms and only theirspores or other resting structures can survive in soil or on the surface of plant parts. Theretheybecomedormantuntiltheyfindthemselvesonthehostorganismagain,wheretheycaninfect,reproduceandgrow,causingplantdiseases.

Control

Moremeansexistforcontroloffungaldiseasesthanforbacterialandviraldiseases.Inordertoproperlycontrolfungaldiseases,itisfirstnecessarytoknow,whichfungal

Figure 1.1 Fungal hyphae. Source: Fungi Kingdom

11

Chapter 1

diseasewearedealingwithandwhatitsecologyis.Thefollowingdiseasemanagementstrategiesarecurrentlyusedforcontrollingfungaldiseases.

Genetic Resistance: Currently there are many varieties of vegetable crops that areresistant to specific fungal diseases. For example, there are some hybrid potatovarieties, which are resis-tant to Phytophthora (late blight).There are also sometomatovarietieswithresistancetoFu-

sarium wilt, that can be planted on land infested with Fusarium. When disease resistance is

available for important diseases, it should be used whenever possible.

Agricultural(cultural)practices:

• Useofdisease-freeseedsandplantingmaterials

• Balancedmineralcontent(fertility)inthesoil

• Efficientwatermanagement

• Sanitation-removalofinfectedplantsorplantremains(debris;

• Crop rotation

• Growingplantsinenvironmentsunfavorableforfungaldiseases

• Proper harvest handling, in order to avoid mechanical damage, cutting, etc

• Properlyselectedstoragetemperature

• Proper spacing and thinning of plants

• Soil solarization

Chemical treatment:

• Use of soil fumigants for the control of certain soil borne fungi

• Use of fungicide seed treatment

• Selection and use of effective fungicides for controlling diseases in the field or greenhouse. Emphasis must be placed on protecting the plants from infection

• Post-harvesttreatmentofproducewithfungicidesduringstorage

Biological control: Selection and use of effective biological control materials and products when available.

Quarantine service: Is used to separate and restrict themovement of infectedplantmaterial.TheintroductionofplantmaterialthatmaycontaindiseasesisenforcedatthebordersofGeorgia.Beforetheplantmaterialcanenterthecountryitmusthavethephytosanitarycertificatewhichisissuedbyanaccreditedlaboratorythatstatesthe material is disease free.

Bacteria

Thereareapproximately1600typesofbacteriaknownintheworld(Fig1.2),someofwhichareharmfulforagricultureandsomeveryuseful,as,forexample,theytakepartindisintegrationoforganicmatter.Approximatelyover100typesofbacteriacauseplantdiseases, which has a negative effect on agricultural crops.

Figure 1.2 Bacteria, prepared by 3D program. Source: Acuariovida


Introduction

Bacteriacanberod-like,spherical,spiralandthreadlike(containingfilaments).Somebacteria canmove through liquid space bymeans of flagella. Somedo not possessflagellaatallandareunabletomove.Manytypesofbacteria,atthevegetativestage,reproducethroughcelldivision.Bacterialdiseasesspreadanywherewhereit iswarmandhumidandareextremelysevereinhumidtropics.

Morphology: Most of the plant pathogenic bacteria are rod-like. If rod-shapedbacteriadevelopspores,theyarecalledbacilli.Cellwallsofmanytypesofbacteriaaresurroundedwithaviscous,stickysubstance,which is thinandformsamucous layer.Mostoftheplantpathogenicbacteriahavethreadlikebranchedflagellawhichmakesthemmobile.Sometypesofbacteriahaveoneflagellumeach,somehaveseveral(polarflagella).Thosewithasingleflagellumarecalledmonotrichous.Lophotrichousbacteriadevelopflagellaononeside,whilethesurfaceofperitrichousbacteriaiscoveredwithflagella.Asmallnumberofbacteriaareimmobile,whilemostofthemmovebymeansofflagella.

Bacteria,whichcanbecoloredbasedonGram’sMethod,aregram-positive,whilethosethatcannotbecoloredaregram-negative.Thedifferencebetweengram-positiveandgram-negativebacteriaisapeptidoglycanlayer(Fig1.3).

Reproduction: Rod-like phytopathogenic bacteria reproduce by asexualmeans,which is known as binary division. This is when cytoplasm internal membrane isdivided inthecentralpartof thecell,asa resultofwhichtwocompletely identicalpartsarecreated.Whencellwallformationiscompleted,bothlayersseparate,split,andtwocellsappear.Beforethecellwallandcytoplasmseparate,thisiswhengeneticmaterialisaccumulated,doubledandredistributedbetweentwonewly-formedcells.Plasmids are also doubled and redistributed between new cells. Bacteria reproduce extremelyquickly.Infavorableenvironmentconditions,theyreproduceevery20-50minutes.

Dispersal:Inmostcases,plantpathogenicbacteriamainlydeveloponhostplantsasparasites.Theyliveonplantsurfaces,especiallyonbuds,aswellasonplantwoundsandinsoil,assaprophytes.Thereareamazingdifferencesbetweentypes,intermsofqualityoftheirdevelopment.Phytopathogenicbacteriamayexistasbiofilms.Somepathogens,e.g.Erwiniaamylovora,whichcausesphytophtorosisonpear,formsapopulationonthehostanddevelopsinuninterruptedinfectioncycles,fromplanttoplant,oftenbymeansof the insect vector.

Bacteriaaretransmittedonthesameplant,aswellasfromoneplanttoanotherbymeansofwater,insects,otheranimalsandhumans.Bacteriathemselvescancoveronlyextremely smalldistances,usingflagella.Rainfallalso transmitsandspreadsbacteriafromoneplanttoanother,aswellasfromthesoiltolowestpartsoftheplant.Insectsnotonlytransmitbacteria,butalsocontributetotheirinoculationintoplants.Duringtheirmovement,birds,rabbits,etc.spreadfromplanttoplantvarioustypesofbacteria,which live on their bodies. Humans transmit them during various agricultural practices, e.g.plantingorseedtransportation,wheninfectionfrequentlyspreads.

Control

Controlling bacterial diseases on plants is more difficult than controlling mostfungaldiseases.Thereareveryfewchemicalsforcontrolofbacterialdiseases;therefore,the emphasis for controlling bacterial disease must be placed on the use of genetic resistance when available and the use of effective cultural practices.

Figure 1.3 Gram-positive (Blue) and gram-negative bacteria (red). Source: Micro Blog

13

Chapter 1

Geneticresistance:

• When available, use varieties with disease resistance against important bacterial diseases

Agricultural(cultural)practice:

Usebacteria-freeseedandplantingmaterial

• Sanitary-hygienicmeasures:disinfestingworkershandsofgraftingtools,etc.

• Sanitation: identification and removal of infected plants and infested plant debris from the planting

• Crop rotation

Chemical treatment :

• Use of solutions containing copper, in order to minimize the risk of spreading of the disease inoculum

• Applicationofantibioticswhenavailable;theycanreducethespreadofbacteriaand aid in preventing infection

• Control disease carriers such as insect vectors.

Biological control: Selection and use of effective biological control materials and products when available.

Quarantine service: Used to separate and restrict the movement of diseases in plant material.The introductionofplantmaterial thatmaycontaindiseases is enforcedatthebordersofGeorgia.Before theplantmaterialcanenter thecountry itmusthavethephytosanitarycertificatewhichisissuedbyanaccreditedlaboratorythatstatesthematerial is disease free.

Viruses

Virusesarepathogenscausinginfection,whicharesosmallthatitisdifficulttoseethem through light microscopes. The simplest viruses consist of nucleic acid, which is surroundedwitha layerofprotein.Virusescarrygenetic informationinnucleicacids,which code three or more proteins. All viruses are obligate parasites, which depend onthehost’scellmechanisms for reproduction.Viruses infectall typesoforganisms:animals, plants, fungi and bacteria.

Morphology:Viruses have a simple structure, which consists of two main parts, nucleic acid and protein. The protein forms a protective shell around the nucleic acid. The protein shell of a virus is called a capsid. Certain viruses have an outer membrane, whichcontainslipidsandproteins(lipoproteinmembrane)

Reproduction: Similartootherorganisms,informationrequiredforthereproductionof viruses is containedwithin thenucleic acid.A very smallnumberofplant virusescontainDNA;mostofthemcontainRNA,similartoinformationalRNAofacell.Hence,viruses have a verywide range of genetic variation and consequently, reproductivecyclesandlifestylesofdifferentvirusesvarygreatly.

Since all viruses are obligate, biotrophic parasites, their lifecycle beginswith thevirusparticlepenetrating into thehost’s cell.Thevirus invades thecytoplasmof theplantcellthroughwoundswhichresultfrommechanicalplantdamage.Thenextphase

Figure 1.4 Viral particle, prepared by 3D program. Source: Virologypedia


Introduction

of viral infection is partial or complete separation of the viral protein shell within the cytoplasmoftheplantcell.Afterthis,expressionoftheviralgenestakesplacethroughthe transcription and translation process. Translation of the virus RNA causes formation of viral proteins in the cytoplasm. Viruses form three types of protein: replicationproteins, which are responsible for nucleic acid synthesis; structural proteins, whichcause formation of the protein shell (capsid) and the so-calledmovement proteins,whichtransportthevirusthroughplantcells.Thenextstageofthereproductioncycleis the spread of the virus into the plant’s neighboring cells. Viruses travel from cell to cellbymeansofnarrowchannels,calledplasmodesmata.Reproductiontimefluctuatesbetweenonetoseveralhours.Virusesinitiallyspreadintothephloem,andthenmoveintosurroundingtissue.Ittakesseveraldaysfortheplanttobecomeinfectedcompletely.

Control

Onceaplantisinfectedbyavirus,thereisnotreatmentthatwillcuretheinfection.Therefore, control of viruses must be preventative; the following methods are recommended to control virus diseases.

Geneticresistance:The use of plants that are resistant to the virus is the most effective meansofcontrol.Unfortunatelyvirusesareextremelyvariableandcanchangetheirgeneticsveryrapidly.Itiscommonforavirustochangegeneticallyinordertobreakdown or overcome disease resistance in plants. When effective disease resistance is available, it should be used.

Agricultural(cultural)practice:Itisimportanttosearchfor(scout)virusinfectedplantsintheplantingandremoveanddestroythemassoonastheyaredetected.Iftheyarenotremoved,theywillserveasasourceofinoculumthatcanspreadthedisease.

• Alwaysusecertifiedvirus-freeseedandplantingmaterial

• Sanitary-hygienicmeasures:disinfestationsofgraftingtools,workershandsandother tools or structures

• Properlyplannedcroprotation

• Control weeds in and around the planting or greenhouse that can serve as a source of inoculum for viruses

• Ifthevirusisspreadorvectoredbyaninsectorotherorganism,thevectorsmustbe controlled

Chemical treatment: There are no chemical treatments for the direct control of virus diseases.Onceaplantisinfected,itisinfectedforlife.

• Chemicals can be used to deactivate the virus on pruning and other tools that can transmit the virus

• Chemicals such as insecticide and nematicides can be used to control the vectors of virus diseases

Biological control: Selection and use of effective biological control methods or products whentheyareavailable

Quarantine service: Used to separate and restrict the movement of diseases in plant material.TheintroductionofplantmaterialthatmaycontaindiseasesisenforcedatthebordersofGeorgia.Beforetheplantmaterialcanenterthecountryitmusthavethephytosanitarycertificatewhichisissuedbyanaccreditedlaboratorythatstatesthe material is disease free.

Figure 1.5 Light microscope picture of nematode. Author: Ernest C. Bernard

15

Chapter 1

Nematodes

Nematodesarenon-segmented,roundworms.Mostaremicroscopicandcannotbeseenwiththenakedeye.Thereareapproximately28,000differentspeciesofnematodes,ofwhichalmost16,000areparasites(Fig1.5).Theyarespreadgloballyandarepresentinvirtuallyeverygramofsoil.Theirlengthvariesfromlessthanonemmto8.4meters(spermwhalenematode).Theyliveatthebottomofthesea,infreshwater,andinsoil.Nematodes can cause plant diseases. These nematodes are plant parasitic nematodes (phytohelminths) and the diseases they cause are referred to as phytohelminthosis.Phytohelminths feedon the contentsofplant cells and caneasily causemechanicaldamage to plant tissues and disrupt life functions.

Morphology:Nematodeshaveoblong,spindleorthread-likebodies,80cmto8mlong,whicharefilledwithliquid.Theyhavenobloodcirculationorrespiratoryorgans.Their digestive system consists of the orifice, pharynx and anus. The neural systemis represented with circular nerve rings surrounding the pharynx. Sense organs areusuallybristlesandpapilae,someofwhichhaveprimitivechemoandphotoreceptors.Nematodes feedbymeansof a stylet,which is aneedle-like structure (mouthpart),by which nematodes can pierce plant cells, inject degrading enzymes and extractnourishment from the plant.

Ecology:Based on their location in or on plants, nematodes are divided into several groups:

• Endoparasites–whichpenetraterootscompletelyandliveinsidetheroot

• Ectoparasites–theyliveonandfeedontheoutsideoftheroot

• Semi-endoparasites–partoftheorganismintheroot

Control

Management of nematodes is difficult. The most reliable practices are preventivemethods, to reduce and avoid

Geneticresistance.When available, use varieties that have resistance to the nematode.

Agricultural(cultural)practice

• Usenematode-freeseedandplantingmaterial

• Avoidthe introductionofsoil (whichmaycontainnematodes)ontherootsoftransplants,ontools,andonequipment

• Properlyselectedseed(crop)rotation

Chemical treatment

• Use of soil fumigants when appropriate

• Use of nematicides when available and appropriate.

Biological control: There are several naturally occurring organisms that providesome level of biological control of nematodes. There are several fungal species that attack nematodes as well as other nematodes that feed on plant parasitic nematodes. These natural biological control organisms aid us in the control of nematode diseases.

Quarantine service: SoilimportationinGeorgiaisrestricted.Moreover,itisillegaltoimport plants with soil on the roots.


Introduction

Plant Parasites

Plant diseases can also be caused by flowering plants. Although their numberis low,parasiticfloweringplantsareextremelyharmful for certainagricultural crops.Theseparasitesaredividedintothreelargegroups:(1)Epiphytes,whichuseplantsassupports;(2)Hemi-parasites,whicharecapableofproducingchlorophyll(forexample,viscumandmelampyrum)and;(3)trueparasitesthatfeedonorganicsubstancestakenfrom plants, e.g. cuscuta, orobanche, anagallis.

Control

Agricultural(cultural)practice

• Useseedandotherplantingmaterialthatisfreefromfloweringparasites

• Mechanicallyremoveparasiticplantsfromtheplantinganddestroythem.

Biological control. Currently there already exist certain preparations against invasiveplantsinGeorgia.Forexample,againstorobanche,wehavedevelopedabiologicalcontrolagentatAgriculturalUniversityofGeorgia.

Quarantine service. Before the plant material enters the country it must have thephytosanitarycertificatewhichisissuedbyanaccreditedlaboratorythattheydoesnot contain seeds of invasive plants.

ABIOTICFACTORSAbiotic factors that affect plant growth include temperature, soil moisture, soil and

water pH, solar radiation, and soil mineral content.

High temperature

High temperature can cause sun burn and desiccation of the fruit and the foliage (Fig 1.6).Hightemperaturesabove32oC result in bleaching of fruit color, formation of water soakedspotsonthefruitskin,andwiltanddrynessof foliage.Highsoiltemperaturealsokillsyoungplantsandcanseveredamagetotherootsystem.

Low temperature

Duringlowtemperature,plantswell-suitedtowarmerclimates,suchaswheatandbeans,undergomoredamage.Lowtemperaturecausesfreezingofyoungleavesandmeristem damage andmay also cause the so-called catface symptoms in tomatoes(Figure 1.7). Low temperature can also cause excessive sweetening of potatoes asa resultof starchhydrolysis into sugar.Damagedependsuponhow long the tubersareexposedtothelowtemperature.Atearlystagesofdevelopmentofpotatoes,lowtemperaturesdamagesvascular tissue causinga ring-likenecrosison the stemsandshoots,whiledamagetotuberscausesnet-likenecrosis.

High soil moisture content

High soil moisture damage is common in areas with heavy rain or due to overirrigation.Ingeneral,poordrainagecancauseseriousdamagetomostplants,resultingin wilting, and yellowing of leaves, root rot, and fungal infection, especially with

Figure 1.6 Tomato sun scald. Source: Owentree

Figure 1.7 Tomato catface caused by low temperature. Source: Owentree

Figure 1.9 How soil pH affects availability of plant nutrients. Gray area depicts a neutral pH of soil, when all nutrients are soluble. Source: Colorado State University Extension

17

Chapter 1

phytophtora(Fig1.8).Highsoilmoistureresultsinrottingofrootsduetolowoxygensupply.Lackofoxygencancausehypoxiaandcollapseof rootcells, anda favorableenvironmentforanaerobicpathogens,whichformnitritesthataretoxictoplants.

HerbicideInjuryHerbicidesareheavilyusedbytheagriculturalindustrytocontrolweedscompetingwithvariouscrops.Severaltypesof injurieshavebeenreportedasa resultofexcessiveand/or improperuseofherbicide.These injuries include foliageturningyelloworbrown,delay inflower, fruit,and leafgrowth,earlyor late leafandfruitdrop,andinseverecases,deathofthecrop.Mostofthedamageiscausedbynotfollowing the manufacturer’s recommendations. Some formulations of herbicides are morevolatilethanothers.Forexample,theesterformof2,4-Dismorevolatilethantheamineform.Insituationsofheavywind,sprayofherbicides,especiallytheesterformof2,4-D,ismorelikelytocausedriftandinjurythaninsituationswithclamwind.

Soil pH

Alkalinityandacidity(pH)ofsoil,water,andothersolventsaremeasuredonascaleof1to14.WhenthepH isat7, thenthesemediums’pH isconsideredtobeneutral.However,whenthepHisbelow7,thesemediumsareconsideredacidicandwhenthepHisabove7,theyareconsideredasalkaline.

As listed inFigure1.9,nitrogen,phosphorus,potassium,calciumandmagnesiumarenotsolubleatacidicconditions (lowpH).Only iron,manganese,copperandzincare solubleat lowpH.Atmoderatealkaline soil (pHabove7),nitrogen,phosphorus,magnesium and calcium are soluble. However, iron, boron, and manganese are less soluble.Onlysolublenutrientsareavailablefortheplanttotakeupfromthesoil.

Figure 1.8 Symptoms of tomato wilting, due to low soil moisture content. Source: Discover Life Organization


Introduction

Mineraldeficiency

Plantsneedmineralsinordertoexist.Certainelements,e.g.nitrogen,phosphorus,potassium,calcium,manganeseandsulfurareconsumedbyplantsinlargerquantities.These elements are called macronutrients, while other nutrients are needed bythe plants in smaller quantities. These are called micronutrients. Both macro andmicronutrients are considered as essential for plant growth. Symptoms of variousnutrient deficiencies develop as a result of low availability of these nutrients (See Annex:NutrientDeficiency).

Toxiceffectsofminerals

In certain cases, soil containsexcessive levelsofminerals,whichmayharmplanthealth.Apartfromthefactthatmineralsdifferintheirtoxicitycoefficient,plantsalsodifferbasedontheirlevelofsensitivitytotheseminerals.Forexample,someplantsaredamagedbyaverysmallamountofnickel,butaretoleranttosignificantamountsofaluminum.Incertaincases,someelementmayhindertheprocessandfunctioningofabsorptionofanotherelement,whichcausesdeficiencyofthelatter.Excessamountofsodiumormagnesiuminthesoilresultsindeficiencyofcalcium.Toxicdosesofcopper,magnesium,andzinc result in irondeficiency.ExcessiveamountsofsodiumchlorideincreasessoilpHcausingso-calledalkalinedamage.Suchdamagevariesamongplantsandismanifestedaschlorosis,growthdelay,foliageburn,wiltanddeathofseedlings.Certainplants,e.g.wheatandapple,areextremelysensitivetoalkalinesoils.Ithasbeendemonstratedthattoxiclevelsofmagnesium,copper,aluminum,andironoftencausedamagetoplantfoliage.Forexample,excessiveamountsofmagnesiumcancauseleafcurl in cotton and bronziness of apple leaves.

Hail damage

Hail damage depends on the plant’s development stage, as well as the size of hail and its duration (Fig 1.10). Damage caused by frost and hail can often be confusedwith pest damage. Severe hail often defoliate trees, resulting in poor fruit set for the followingyear.Areaspronetospringfrostarenotsuitableforgrowingfruittreesandvegetables.Temperaturedropsbelowfreezingduringbloomcandestroyanentirecrop.Siteselectionisverycriticalforreducingfrostdamage.Siteswithgoodairdrainageisessentialforearlyandlatefrostdamage.

DISEASEDIAGANOSTICQuickandaccuratediagnosticsofthediseaseisnecessarybeforeweplanrelevant

preventivemeasures. This is the first stage, which, if implemented improperly, mayhavegraveresults.Moreover,thiswillhelpustoavoiddiseaseepidemics. Inordertodeterminewithwhichdiseasewearedealing,itisfirstnecessarytoknowhowahealthyplantlooks.Atthenextstage,wemustobservediseasesymptomsandsigns.Finally,weneed to have information about conditions of the environment, where the plant grows: temperature,soilcomposition,usedagro-technicalpractice,precedingcrop,diseasesknowntoexistinthisregion,etc.

Figure 1.10 Symptoms of hail damage in tomato. Source: Wikimedia Commons

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Chapter 1

Differentiationbetweenabioticandbioticfactors

Inordertoaccuratelydeterminewhetherthesymptomsareduetoabioticorbioticfactors,itisessentialtoconductproperdiagnosisbyobservingdiseasesigns,symptomsand their dissemination in field conditions.

• Ifsymptomsarespreadtoallplantsinthefield,inmostcaseswearedealingwithabioticdamage.Duringbioticdamage,onlythehostplantgroupbecomesinfected.

• Symptomscausedbyabioticfactorsoccurmostlyatthesamestageofdevelopmentin various plants, while biotic infection induces various disease stages on various plants and plant parts.

• Todifferentiate betweenbiotic and abiotic is the disease separating line.Duringabioticdamage,diseasedtissueisseparatedfromthehealthytissue,whileduringbioticdiseasesthereisatransitionalareabetweendiseasedandhealthytissue.

Inthecaseofabioticfactors,itisnecessarytoconductleaf,fruit,and/orsoiltestinginordertodeterminetheadequacyofthemineralstakenupbytheplant.

Collecting samples

Inorder for samples tobe collectedproperly andnotbe further infectedduringtransportation,itisnecessarytoobserveminimalsanitarystandards.(1)Determinethehostplant.Ifitisunknown,collectadequatesampleofinfectedandnon-infectedtissue.(2)Observesymptomswhilecollectingsamples.Ifpossible,uprootthewholeplantandplaceitinpaperbags;neveruseaplasticbag.(3)Samplehastocontainbothdiseasedandhealthypartsoftheplant.(4)Toavoidcontamination,avoidplacinginfectedandnon-infected tissue in the same container.Write variety, date, location, and stageofdevelopmentofeachofthecollectedplanttissueonthebagandinyournotebook.Forleafnutrientanalysis,collectfullydevelopedleavesfromthemiddlesectionofaoneyearoldshoot.Collectshootsfromvariouspartsoftheplant.Donotcollectdiseasedordamaged tissue.

Laboratorytestsfordiseaseidentification

Diseasesoftencannotbediagnosedcorrectlyjustbyknowingthesymptomsandsigns.Inordertodothis,itisnecessarytoinspectmaterialsinlaboratoryconditionsinordertocorrectlyidentifythecause.

Incubationingrowthchamber

Inorderforthepathogentobegingrowinginthelaboratory,itisnecessarytoplaceit inahumidchamber.Outside laboratoryconditions, thiscanbedonebyplacingawetsheetonapetridishorinaplasticbox,whichcreatessufficienthumidityforthepathogen to start growing so that it can be observed and isolated. Viral diseases cannot be identified with this methodology. Several molecular biology techniques or theinoculationofindicatorplantsarerequiredfortheidentificationofdiseasescausedbyviruses.

Isolation of a fungal pathogen often requires growing it on growth medium inpetri plates, which enables us to separate specific fungal parasites. Also in the case of

DIAGNOSTICFORMSAMPLE

1.Cerealorplantname

2.Describethegeneralpictureofdiseasespreading

3.Describesymptomsontheplant

4.Picture

5.Whendidsymptomsappear:Day Week Month

6.DescribeconditionsbeforesymptomsappearedTemperature

Rain Other

7.Croprotation:twoyearsago oneyearago

8.Soiltype

9.pH

10.Soiltestresults

11.Addingnitrogen

12.Useofchemicalsubstances:

Fertilizer form of use

Herbicide whendidyouuseit

Insecticide whendidyouuseit

13.Chemicalsusedthepreviousyear 14.Conditionofsurroundingplants


Introduction

21

Chapter 1

bacteria, part of the plant is crushed in water and a suspension is transferred to the growth medium, from where bacteria can be separated. When an organism is isolated, it isnecessarytoidentifyit.Inordertoidentifythedisease,qualifiedlaboratorypersonnelare required who will be able to identify it accurately under the light microscope.Simultaneouslywithdisease identification, it is necessary todeterminewhether thisorganismistheprimarycauseofthedisease.Inordertodothat,itisnecessarytorepeatKoch’spostulateand infectahealthyplantwiththeorganism, identifiedbyus. If theinoculatedplantdevelops thesamesymptomsas thediseasedplantandwecan re-isolatethesameorganism,thenwearedealingwiththeorganismwhichistheprimarycause of this disease.

ModernDiagnosticTests

Aswehavealreadynoted,disease identificationplaysthegreatestrole indiseaseprevention. Hence, new technologies have appeared on the market that enable us to identifypathogensquicklyandwithhighsensitivity,whichinturnmakesitpossibletoavoidconductingclassical,long(four-tofive-day)laboratoryexperiments.

Immunostrips– arequick andenableus to identifydiseaseswithout any laboratoryresearch under field conditions. Agdia (www.Agdia.com) is one the mainmanufacturersofthesetypesofproductsandhasmanyoftheidentificationstripsforidentifyingbacteria,fungiandviruses.

ELISA–(EnzymeLinkedImunosorbantAssay)isamethodwhichmakesitpossibletodetermineexistenceofspecificantigens(virus,mycoplasma,bacteria,etc.).Antigen-specific antibodies are produced in mammals, which enables us to identify thediseasewith95-100%accuracy.ELISAisoftenusedinimmunostrips.

PCR –PolymeraseChainReactionisabiochemicalmethodinmolecularbiologywhichenablesustoamplifygeneticcodesofspecificpathogens.Thistechnologycanbeused on bacteria as well as fungal diseases and viruses. Reagents for PCR tests are producedinGeorgiabyL.T.D“Oxygen”.www.oxgen.ge

NextGenerationSequencing–isamolecularbiologicaltechnology,bymeansofwhichwecandeterminegeneticsequenceofthepathogen.Itisnowadaysbeingwidelyintroducedinphytopathology,whichwillenableustoidentifydiseaseswith100%accuracyinnearfuture.

INTEGRATEDMANAGEMENTOFPLANTDISEASESInorder toeffectivelypreventandmanageplantdiseases,weneed todevelopa

disease management program that integrates all available methods of disease control. Theseinclude:(1)thedevelopmentanduseofdisease-resistantvarieties;(2)theuseofcultural control (agricultural)practices thataid indiseasemanagement; (3) selectionanduseofeffectivediseasecontrolchemicalswhenappropriate.(4)Biologicalcontrolwhenavailable;and(5)theuseofregulatorypracticessuchasQuarantineprotection(seeFig.1.11).Theintegratedmethodofplantdiseasecontrolenablesustocarryoutcomplexcontrolprogramsforthepreventionofdiseases.Itshouldbenotedthatthegeneral approach to plant disease control is usually preventative or protectant. It isdirected at the prevention of plant diseases rather than treating them after the plant is infected.


Introduction

GeneticResistance: Thedevelopmentanduseofdisease-resistantvarieties is themost efficient and economicalmethod for controlling plant diseases. Classical plantbreeding and genetic transformation techniques, has resulted in many varieties ofseveralvegetablecropswithresistancetomanyimportantplantdiseases.Forexample,therearewidelyusedvarietiesoftomato,eggplantandothervegetablecrops,thatareresistant to Fusarium wilt. With soil borne diseases such as Fusarium and Verticillium wilt, it is not possible to grow susceptible varieties in areas that are infested with these fungi. The use of resistant varieties allows us to grow valuable vegetable crops in areas whereitwasnotpossiblebefore.Theuseofresistantvarietiesalsogreatlyreducesourneedtouseexpensivediseasecontrolchemicalssuchasfungicides.

Cultural Control Methods (Agricultural Practices): The use of effective cultural practicesarevery important for controlofplantdiseasesandarean integralpartofthe integrated diseasemanagement program. Any practice that helps to make theenvironment less conducive to disease development is of great value. At times, thesemethodsmaybethebestoronlymeansofcontrollingaspecificdisease.Someimportantcultural(agricultural)practicesincludes.

• Crop rotation.Thispracticeenablesustoincreasesoilqualityandatthesametimetoblockthecycleofplantpathogensfromoverwinteringinthesoil.Croprotationreducespathogenpopulationsbyremovingasuitablehostplantforthepathogentosurviveonfromyeartoyear.Carefullyplannedcroprotationpracticescanaidinincreasingsoilfertility,preventingsoilerosion,andpreservingthewaterbalance.Allofthesebenefitsenableustohavehealthyandproductiveplants.

• Selectionanduseofpathogen-freeseedandotherplantingmaterials. Inordertoprevent the introduction of plant diseases (pathogens) into our fields andgreenhouses, it isnecessary tousecertified (disease free)plantingmaterials. Seedandotherplantingmaterialshavetobepuretovariety,cleanandofhighquality.Iftheydonotmeetthesecriteria, theydonotemergeproperlyand inmanycases, theyproduce plants that are infected with diseases.

• Soil. In order for plants to be healthy and productive, it is necessary for the soiltohavetheproperpHandmineralcontenttoprovideadequatenutritionfor theplants. Apart from chemical composition of the soil, attention must also be paid to its physicalcondition.Practicessuchasdeepplowingmayplacesoilbornepathogensdeeperinthesoilwheretheyarenotabletosurvive.

• Sanitation practices. Theseareaimedatreducingoreliminatingplantpathogens.Itisimportanttoinspecttheplantingregularlyandremoveplantsthatarediseasedand destroy them.Many diseases overwinter in plant remains (debris).With suchdiseases,itisnecessarytocollectanddestroyoldplantremains.Forexample,potatoand beet remains can contain a number of important viral, fungal and bacterial plant pathogens. Also, attention should be given to sanitary conditions of agriculturalequipment. For example, potato virus X spreads by means of contaminatedagricultural equipment and humans walking through the plants. Soil cultivationequipmentshouldbewashedregularly,inordertoavoidtransferofpathogensfromone location to another.

Direct protection of plants by means of chemical control: Chemical substances that are toxic to pathogens are used for plant protectionworld-wide in the field, ingreenhouses, and sometimes in storage areas. Based on the type of pathogen theycontrol, chemicals are classified as fungicides, bactericides, nematicides, or herbicides.

Figure 1.11 Schematic illustration of integrated disease management strategies

23

Chapter 1

Certainchemicalshaveabroadspectrumofactivityandareeffectiveagainstawiderange of pests or diseases. For example, some fungicides are capable of controllingfungi inseveraldifferentgeneraand families,unlikeothers,whichaffectonlyoneora fewspeciesof fungi.Due to theirexpense,diseasecontrolchemicalsaregenerallyusedonlyonhighervaluecrops.InGeorgia,sixtypercentofchemicalsareusedforfruitdiseasecontrol,while25percentareusedonvegetables.Somechemicalsareusedforprotectingthepartsoftheplantwhichareaboveground.Thesearegenerallyreferredtoasfoliartreatments.Otherchemicalsareusedasseedprotectants.Somechemicalsareusedfordisinfestingthesoilingreenhouses,woundsontreesandaspost-harvesttreatmentsforfruitsandvegetablesinstorageareas.Insecticidesareusedforcontrollingthe insects that transmit certain diseases. Some chemicals have therapeutic effect. However,mostchemicalsareusedprimarilyasprotectantsandareaimedatpreventingplantdiseasesratherthantryingtoeradicateorcurethemafterinfectionhasoccurred.

Biological control: This implies the use of super parasites against organisms causing diseases. All pathogens (fungi, bacteria, nematodes and viruses), have their ownpathogens. For example, bacteriophages or phages are viruses that are naturalpathogensofbacteria.Somemicroorganismsproduceantibioticsthataretoxictopathogens.Somebacteriaproducefermentationproductswhichdestroypathogenstructures such as cell walls. Microorganisms with such qualities are used asantagonistsforbio-controlofdiseases.Scientistsareusingmicroorganismssuchasthese to produce new biological control products that are effective for controlling manyplantdiseases.

Regulatory protection: Plant quarantine (quarantine inspection) is an importanttoolforpestanddiseasecontrol. Itsmaingoal istoprotectacountryorregionfrom


Introduction

the importationofexoticpestsanddiseasesthatarenotcurrentlypresent.Whenanalienorexoticpathogenentersanewarea,theycanresultinsevereepidemicsduetothelackofnaturalbiologicalcontrolorganismsinthenewenvironment.Itisnecessaryandveryimportant,inanycountrytointroduceanddevelopquarantinesystemswhichwill prevent the importation of plant pests and plant diseases as well as plant products andsoil fromothercountries.Regulatory responsibilitiesmayalso includepathogenprevention through the production of plants in locations where plant pathogens are notpresentorendemic.Forexample,toproducevirus-freepotatotubers,potatoescanbegrowninhigh-mountainousregions,wherethevectorofthisvirus isnotpresent.This same procedure can be used with other crops and plant diseases

25

Chapter 1

ANNEX1.NUTRIENTDEFICIENCy

Mineral Function Symptom Picture

Nitrogen (N) Represented in almost all plant substances

Plant growth is weak and its coloring is light green oryellow,finallybecomingreddish

Phosphorus (P) RepresentedinDNA,RNAand plant phospholipids

Plant growth is weak and orange lines are noticeable on foliage

Potassium (K) Catalystofmostreactionsinthe plant

Plant’s stem is weak, dieback begins. Leaf chlorosisandgrayingofleaftipsbegin,multiplegrayspots also appear

Chapter 1


Introduction


Iron (Fe) Catalystofchlorophyllformation

Leavesstartturningyellow,but plant veins remain green

Magnesium (Mg) Componentofchlorophyllandvarious(ferments)

Leaves develop chlorosis andmaycurlupwardsandbeginturningyellow

Calcium (Ca)Functions in membrane conductance, forms salts with the presence of pectin

youngleavescurl,theirsizeisabnormalandtheyarecoveredwithgrayspots.Bottom of fruit begins to rot(blossomendrot)

27

Chapter 1


Boron (Br) Participates in sugar transportation

Plant growth is weak, chlorosis is visible on foliage and leaves curl. Cells on fruit, around stems, stiffen

Sulfur (S) Component of amino acids andcoenzymes

youngleavesarepaleincolororyellow,withoutanyspots

Zinc (Zn) Zincisusedinoxidationofauxinsandsugars

Necrosis can be observed on the leaves, between veins. Number of leaves on a plant also diminishes


Introduction


Manganese (Mn)

Component of reactions which participate in the plant’s respiration, photosynthesis,andnitrogen consumption

Leaves begin to develop chlorosis but small veins remain green

Molybdenum (Mo) Main component of nitrogen reductase

Symptomsareverysimilartonitrogendeficiencysymptoms,butlackofmolybdenumisnotgenerallycharacterizedwithreddish coloring

Copper (Cu) Componentofoxidationferments

Leaftipsturnyellow,leaveschange color and curl

29

Chapter 2

Eggplant (Solarium melongena var. exculentum), also known as aborigine andberinjal,isamemberoftheSolanaceaefamily,whichincludespeppers,tomatoes,andpotatoes.Thereareseveraltypesofeggplantfruitsgrowncommercially.Theyrangeincolorfromthemostcommonlyplanteddeeppurple/blackvarieties,rose,lavender,andwhite,tofruitswithstreaksofpurpleorpink.Fruitsalsovarygreatlyinshapesandsizesrangingfromsmallandlargeoblongvarieties(includingthecommonlygrownblockyvarieties),long,thin,cylindrical(Orientalvarieties),andbite-sizebabyvarieties.Anothertype of eggplant (Solarium integrifolium), commonly known as Scarlet, JapaneseGoldenEggs,TurkishOrange,orPumpkin-On-a-Stick,isgrowninAsiaandAfrica.Thistypehasredandorangefruitsthatareusuallysmallandhollow.

ClimaticRequirements

Eggplant is a warm-season crop that requires between 65 to 85 days fromtransplanting to reach marketable size. The optimum soil temperature for seed germination is between 24° and 32°C, while the optimum temperature to starttransplantinginthefieldisabove18°Cwhenthedangeroffrosthaspassed.Transplantsgrowbestwhenairtemperatureisbetween24°and30°C.

SoilRequirement

Eggplant can grow successfully in most soils, however, plants do best in well-drainedsandyloam,loam,orclayloamsoilswithagoodsupplyoforganicmatterandanoptimumpHof6.0to6.5.Whencovercropsareused,theyshouldbeplowedunderat least one to two months before planting in order to allow for proper decomposition. Tominimizetheriskofsoil-bornepests,eggplantshouldnotbegrownfollowingothermembersofthesamefamilyliketomatoes,peppers,potatoes,orwithintwotothreeyearsfollowingeggplantproductioninthesamefield.

FertilityRequirements

Soil analysis is very important for growing any food crop profitably. Collect soilsamples fromeachplot that you intend to crop, either in thewinterorearly spring.DependingonsoilpH,apply the recommendedamountof lime (if soilpH is low)orgypsum (if soil pH is adequate) at least two to threemonths before planting. If soilanalysisindicatesthatmagnesiumislowusedolomitelime,andifmagnesiumlevelisadequatethenapplynon-dolomitelime.

Application of appropriate amounts of other nutrients at the correct time will make significantimprovementstothequalityandquantityoffruitsproducedandcanpromoteearlierharvest.Ageneralrecommendationforeggplants istoapplyabout60to70kgperhectareofactualnitrogenand90to120kgperhectareofeachofphosphorusandpotassium.Whensoilanalysishasnotbeendoneapplyabout1,000kgperhectareoffertilizersuchas6-12-12or5-10-15.Besurethefertilizerplacedwithintherowsisbandedormixedwellbeforetransplanting.Broadcastandincorporate50percentofthefertilizerbeforetransplantingandapplytheremaininghalfwithintwoofweeksaftertransplanting.

When fruits start to set, side dresses the rows with 25 to 35 kg of nitrogen perhectare and then twicemorewith the same rate at 10 to 14day intervals.Nitrogensidedressingapplicationsispreferablyaddedascalciumnitrate,butitdoesnothaveto be incorporated. Calcium nitrate but not ammonium nitrate reduces the incidence of blossom end rot in eggplant fruits. For more information about blossom end rot control refer to the tomato and pepper chapters.

Eggplant Chapter 2


Eggplant

Seed Rate and Spacing

It is estimated that 100 grams of seed will produce about 9,000 transplants.Transplantsshouldbebetween15and25cmtallwith four toeight leaves,but theyshouldnothaveanyflowerbuds,flowers,orfruits.Transplantsareusuallyspacedat60to75cmapartwithinarowand100to120cmapartbetweenrows.

Because of the short time between planting and harvest (60 to 90 days), it isrecommendedthateggplantsshouldbeestablished fromtransplants rather thanbydirectseeding.Insomeareas,twocropscanbeharvestedfromthesameplants.Afterthefirstcrop,thetopoftheplantsarecutbacktothesoilsurface.Withinafewdays,newleavesemergefromlatentbudsonthestemsandnewflowersandfruitsdevelopwithin85to90days.Adoseofcalciumnitratemaybeappliedwhenatleastsixleaveshave emerged from the remaining shoots.

Harvesting and Postharvest Handling

Because fruitsare ready forharvest in themiddleof the summer, fruit shouldbeharvestedinthecoldestpartoftheday,usuallyearlyinthemorning.Fruitsshouldbekeptcoolbysprayingthemwithpotablewaterandkeepingtheminshadedareas.Fruitsshouldbecooledassoonaspossible.However,eggplantfruitsareverysusceptibletochilling injuryat10°Cor lower temperature.Thebest temperature to storeeggplantfruitsisbetween12°to13°Cwith90to95percenthumidity.Fruitswillkeepforaboutseventotendaysatthisoptimumtemperature.

EGGPLANTDISEASESThere are several important diseases that affect eggplant. The most important

diseasescausedbyfungiinclude:greymold,Phomopsisblightandfruitrot,Verticilliumwiltandearlyblight.CucumberMosaicisthemostimportantdiseaseinGeorgiathatiscausedbyavirus.Stolburisanimportantdiseasethatiscausedbyaphytoplasmandbacterialspotisthemostimportantdiseasecausedbybacteria.

EggplantDiseasesCausedbyFungiGrayMold

CausalAgent–Botrytiscinerea.Thecausalfungusisasaprophytethatcancolonizedeadordyingtissuesofmanyplantsspecies. It isacommonpost-harvestpathogenonmanyfruitandvegetablecropsworld-wide.Itsurvivesassclerotiaininfectedplantdebrisontoporinthesoil.Itcanalsosurviveinthesoilintheabsenceofplantdebrisforatleasttwoyears,andonvarioussurfacesinstorageandpackingfacilities.Leaves,petioles and fruit can be infected in the field, and ripe fruit can be infected during storage.Thefungusentersandrapidlycolonizeswoundsmadeduringharvestingandhandlingprocedures or other causes.The fungusmay alsopenetrate tissuedirectly.Free water on the surface of the plant promotes infection. The optimum conditions for infectionanddiseasedevelopmentare temperatures ranging from18° to23°C,highhumidityandprolongedperiodsofwetness.

DiseaseSymptoms:The disease develops both on green in the field and ripe fruit, during storage. Fruit develops dark wet spots. Under favorable conditions, the spots increase in size and eventually may cover the entire fruit surface. Especially underconditionsofhighhumidity,diseaseareasbecomecoveredwithathickgray layerof

Figure 2.1 Symptoms of gray mold on eggplant. Source: Caring Plants

31

Chapter 2

fungusmyceliumandconidia.Thislayerofgrayfungalgrowthisverycharacteristicofthediseaseandishowthediseasegotitsname“graymold.”

Control

• Useproperagriculturalproductiontechniquesthatminimizedamagetotheplantandtaprootandresultsinhealthyvigorousplants.Handleplantscarefullyduringharvest and packing to prevent damage;

• Maintainoptimalstorageconditions(temperature:1°to2°C,relativeairhumidity:80-85percent);

• Sanitation-Carefulandthoroughcleaninganddisinfestingofstorageandpackingareas;

• Sanitation-Removeanddestroyinfectedplantpartsandfruits inthefieldandinstorage. Special care should be given to removing infected fruit during sorting and packing;

• The use of effective fungicides can be useful in controlling the decease.

Phomopsis Blight and Fruit Rot

Causal Agent – Phomopsis vexans.The fungus survives in crop debris on top of and in thesoil.Theproductionofeggplant in thesamefieldyearafteryearwithoutcrop rotation results in a buildup of the fungus in the soil and the disease continues to get worse. The fungus is also seed borne and can be introduced into new plantings on infectedtransplants.Diseasedevelopmentisfavoredbyhot,humidandwetweatherconditions.Thefungusspreadsprimarilybysplashingwaterfromrainfallandoverheadirrigation.

DiseaseSymptoms:Thediseasemostcommonlyaffectsthefruit;however,itcanalso affect leaves and stems in the field. Symptoms on fruit begin as pale sunkenareas which are oval in shape, these areas grow bigger and become depressed; lesionsmay coalesce to cover all ormostof the fruit.As the spotsmerge the fruitrots. Rotted fruit becomes coveredwith smallwarts,may be deformed and finallydries down and mummifies. Seed from such fruit can be infected with the fungus. Infectedseedscansurvivetocarrythefungusintonewplantings,ordie.Asseedlingsemergefromdiseasedseeds,theycommonlydampenoffanddie.Thecausalfunguscan also affect the root neck of the emerged plant, which wilts and rots at the neck, turnsdarkbrownandfinallycollapses.Stemsofdiseasedplantsdevelopblackdots.When leaves become diseased, their surface forms round or angular black spots, withathinmargin.Diseasedfoliagedoesnotcausesignificantdamagetotheplant,but the fungus reproduces on infected leaves increasing inoculum for spreading the disease to the fruit. When stems are diseased, damaged areas turn light in color. When damaged areas surround the stem, the part of the plant which is above the damaged areafirstwiltsandthendriesandeventuallydies.

Control

• Alwaysstarttheplantingusingdiseasefreeseedortransplants;

• Croprotation-usearotationthatexcludestheproductionofeggplantforatleasttwotothreeyearsorlonger;

• Sanitation-Removeanddestroyinfectedplantpartsandfruits inthefieldandinstorage. Special care should be given to removing infected fruit during sorting and packing;

Figure 2.2 Symptoms of phomopsis blight. Source: WikiGardener


Eggplant

• The disease is seed borne so effective fungicide seed treatments are recommended;• The use of effective fungicides can be useful in controlling the disease.

Verticillium Wilt

Causal Agent – Verticillium dahliae.Verticilliumwiltcanbeaveryseriousdiseaseoneggplant.ThefungushasaverywidehostrangewhichincludesmostoftheplantsintheSolanaceaefamilyincluding:tomato,potato,pepper,andmanyothers.ThehostrangealsoincludesmanyfruitandvegetablecropsthatarenotintheSolanaceaefamily.The fungus produces survival structures called microsclerotia that allow the fungus to surviveinsoilindefinitely.Thediseaseisfavoredbycooltemperatures.

DiseaseSymptoms:Symptomsusuallyappearatthebloomorbuddingstagesoftheplant.Symptomsappearfirstonlowerleavesandthenspreadupwardsontheplant.Symptomsincludeyellowblotchesonlowerleavesfollowedbyarapidyellowingoftheentire leaf and the edges of affected leaves often roll inwards.

Leavesthatareseverelyinfectedturnbrown,dryupanddie.Often,onlytheleavesat the tip of the plant do not wilt and remain green.

Control

• Select and use disease resistant varieties when available;

• Croprotationisoflimitedvaluebecausethefunguscansurviveindefinitelyinsoil.However, crop rotation can help to reduce the population of the fungus in the soil. Ifcroprotationisused,usearotationthatexcludestheproductionofeggplantandothersusceptiblecropsforatleastthreetofouryearsorlonger;

• Sanitation-Removeanddestroyinfectedplantpartsandfruitsfromthefield;• Soil fumigation.

EarlyBlight

Causal Agent – Alternaria solani.Thediseaseisverycommonandcaninfectmostplantsinthesolanaceaefamily.Thefungusinfectsanddamageseggplantleavesandfruit. Under condition favorable for disease development, the disease can result in defoliationandfruitrotresultinginseverecroploss.Thediseasecanspreadveryrapidlyafterfruitset.Theriskoffruitinfectionincreaseswithrapidalternationsbetweenrainyandhot,dryweather.

DiseaseSymptoms:Onleaves,brown-blackspotsdevelopthatcancovermostoftheleafsurface.Intimespotsdevelopcharacteristicconcentricringsoflightanddarkcolorwithinthem.Severelyinfectedleavesturnyellow,dry,andeventuallydie,resultingindefoliationoftheplant.Onfruit,largesunkenlesionsoftenwithconcentricringssimilarto those on leaves develop at the stem end of the fruit. Affected areas on fruit often have ablackvelvetytexture.Intimethefruitmaycompletelyrot.Invasionofaffectedfruitsbysecondaryrotorganismsincreasethepotentialforfruitrot.

Control

• Sanitation-Removeanddestroyinfectedplantpartsandfruitsfromthefield;

• Destroy any volunteers solanaceous crop plants and weeds (tomato, potato,nightshade,etc.)fromwithinandneartheplanting;

• Usecroprotationthatexcludestheproductionofeggplantandothersusceptiblecropsforatleasttwotothreeyearsorlonger;

Figure 2.3 Symptoms of verticillium wilt. Author: Lindsey du Toit

Figure 2.4 Symptoms of alternaria solani in eggplant. Source: Plant Village

Figure 2.5 Symptoms of cucumber mosaic virus. Source: Diseases-Pepper and Eggplant

Figure 2.6 Symptoms of stolbur in eggplant. Source: Legumicultura

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Chapter 2

• The application of effective fungicides is important for controlling this disease. Begin fungicide applications at the first sign of disease.

EggplantDiseasesCausedbyVirusesandPhytoplasmasCucumberMosaicVirus(CMV)

Causal Agent – Cucumber mosaic virus: Cucumber mosaic virus can infect a large numberofcropplantsandweeds,especiallyinthesolanaceaefamily.Limitedspreadofthevirusmayoccurinthefieldthroughthehandlingofplantsbyhumans.ThemostimportantmeansofspreadisbyAphids.Atleastthreespeciesofaphids(andprobablymore)arevectorsofthevirusandareveryefficientinspreadingit.

DiseaseSymptoms:Leaves near the top of the plant are small, wrinkled and often haveayellow-greenmosaicpattern.Leavesmaybedeformed.Lower leavesdevelopchlorotic spots with dark circumferences. Flowers that form on infected plants are often sterile.

Control

• Destroy any volunteer solanaceous crop plants and weeds (tomato, potato,nightshade,etc.)fromwithinandneartheplanting.Theseplantscanactasasourceofthevirusiftheybecomeinfected;

• Control the aphid vectors that are responsible for most of the virus spread through the use of effective insecticides.

Stolbur

Causal Agent – Phytoplasma. Spread of this disease depends significantly uponintensity of reproduction of the pests, which transmit the phytoplasma. The mostimportant vectors are insects in the hyalestes family such as crickets. Cricket larvaeoverwinteronrootsofvariousplants,ofwhichfieldbindweedisespeciallysignificant.Stolbur is characterized by clearly expressed cyclic nature; after epiphytoty ends,considerable weakening of disease spreading can be observed.

Disease Symptoms: First signs appear as weak chlorosis and shrinking of leaves. Lateron,diseasedplantscanbeeasilydistinguishedfromhealthyones,sincehigherleavesdevelopstrongchlorosisandonlythetissuelocatednearleafveinsretainsgreencolor. Leaves tear and are violet in color. With time, damage spreads to lower leaves as well.Simultaneouslywiththisprocess,leavesbegintofall.Onlyyoungleaves,locatedatthe tip of the plant, do not fall. Fruit formed before disease occurrence wilts.

Control

• Instronglydamagedfields,itisrecommendedtoplanteggplantearly,inordertobeaheadoftheflightsoftransmittinginsects,whichbegininthebeginningormiddleofJune;

• Eggplantshouldbeplantedasdenselyaspossible;

• Seedingcornorsunflowerbetweeneggplantplants iseffective,as itcomplicatesflyingofinsectpests;

• Timelychemicalsprayingagainstcrickets(advantageshouldbegiventosystemicchemicalpreparationswithaprolongedeffect).

Figure 2.8 Symptoms of chilling injuries. Source: Canadian Food Inspection Agency


Eggplant

EggplantDiseasesCausedbyBacteriaBacterial Spot

CausalAgent–Xanthomonascampestris.Thediseaseiscausedbybacteriaanditcanaffectseveralotherplantsinthesolanaceaefamily.Plantsmaybecomediseasedbothinopenfieldproductionandinplantingsprotectedbyhightunnelsorgreenhouses.Thepathogensurvives incropdebris inandontopofthesoilandinseeds. Infectedseeds and transplants are the most important source of inoculum for the disease. The pathogen is not soil borne in the absence of plant debris. The bacteria penetrate leaves and fruit through natural opening or wounds. The optimum temperatures for disease developmentrangefrom15°to30°C.Thebacteriacanbespreadfromplanttoplantbysplashing water from rain or overhead irrigation, contaminated tools and implements and worker’s hands.

DiseaseSymptoms:The disease manifests itself on the plant’s foliage, fruit and stems. Leavesdevelopsmallblackspotswithyellowhalosormargins,which,intime,growtothediameterof2-3mm.Spotsonstemsandleaves,areoblonginshape.Fruitinitiallydevelopsbulgingdotswithwet(water-soaked)edges,whichlatergrowinsize,reachingthediameterof6-8 cmandfinallydevelop intoulcers. Ifplantsbecomediseasedatinitialstagesofdevelopment, theyusuallydie. If infectedplantssurvivethequantityandqualityofharvestedfruitisgreatlyreduced.

Control

• Alwaysstarttheplantingwithdiseasefreeseedortransplants.Ifdiseasefreeseedcannot be obtained, hot water treatment of infected seeds should be considered;

• Usecroprotationthatexcludestheproductionofeggplantandothersusceptiblecropsforatleasttwotothreeyearsorlonger;

• Ifthediseaseoccursingreenhouses,itisnecessarytoreplacethesoilordisinfectit.

• Sanitation - Removeanddestroy infectedplantparts and fruits from thefieldorgreen house;

• Storagefacilities,greenhousebenches,trays,implementsandequipmentshouldbethoroughlydisinfestedwithchlorine(40gramsperliterofwater);

• Chemicalcontrol-Foliarsprays(Copper,manganese)canbealsousedinfieldduringthe growing season or on transplants in the greenhouse.

PhysiologicalDisordersChillingInjury. Chilling injured fruits develop pitting, bronzing, and pulp browning if

storedforlongperiodbelow10°C.Chillinginjuredfruitsarenotmarketable.

Bruising.Eggplantfruitsareverysusceptibletobruisinginjury.Properhandlingofeggplant fruitduringharvestvery is important.Fruits shouldbeharvested inplasticrather than metal buckets and should be stored in cardboard with appropriate ventilationholes. Boxeswith single cells, rather than loosefill, arepreferred for fruitstorage.

Figure 2.7 Symptoms of bacterial spot in eggplant. Source: Canadian Food Inspection Agency

35

Chapter 3

The potato (Solanum tuberosum)belongstothesolanaceaefamilyoffloweringplants.Potato has become one of the most important staple foods around the world, ranked thirdafterriceandwheat.Inadditiontobeinganimportantsourceofcarbohydrates,potatoes also contain several vitamins and minerals including vitamin A and C, niacin, phosphorous,andpotassium.AccordingtotheUNFoodandAgricultureOrganization,worldproductionwasestimatedat365milliontons(Source:FAOSTAT,2014).Priorto1990,thebulkofworldproductionwasintheUSandEurope.However,in2005morepotatoes were grown in the developing world than in the US and Europe.


Potatoplantsareveryadaptableandwillalmostalwaysproduceadecentcrop,evenwhenthesoilandgrowingconditionsarelessthanoptimum.Theycangrowfromsealeveltoupto4,700metersabovesealevel.Potatoesareveryaggressiverootingplantsthat will produce the best crop when grown in full sun. Plants will not start to grow until the soil temperature has reached about 7oC.During tuber formation (bulking),vines often compete with the tubers for the same limited nutrient resources. Therefore, excessivevinegrowthduringbulkingreducestubergrowth.Several factorscanshiftthe balance between vine and tuber growth, and one of these is temperature. High soiltemperatureoftendelaystubergrowthandencouragesfoliagegrowth.Forrussetcultivars, like Russet Burbank, the optimum soil temperature for tuber growth is about 16°C,whiletheoptimumairtemperatureforvinegrowthisabout25°C. It ispossibletomaintain cool soil temperatureswhen plants are healthy and have a full canopythatwillprovideshadetokeepthesoiltemperaturecloseto16°Cforoptimumtuberdevelopment.Potatoplantsproducethebestcropwhengrowninlight,loose,andwell-drainedsoils,withaslightlyacidicpHintherangeof5.0to6.5.

Cultivars

There aremore than 4,000 native varieties andmore than 180 species of potatogrowingmostlyintheAndesregionofSouthAmerica.Potatotuberscanbeeatenatanystageofdevelopment.Typically,however,acommercialviablecroprequiresbetween100–150daystogrow.Severalmeansofclassificationarebeingusedinpotatoincludingthe following:

- Use. Fresh market and processing varieties.

- Skin finish.Russetandnon-russetvarieties.ThemostwidelyplantedvarietyisRussetBurbank.

- Colour.White,red,yellow,andpurple/bluevarieties.

- Size.Baby,fingerling,andpetite.

Field Preparation and Planting

Typically,thelandmayhavebeenplantedwithanothercroporleftfallowthepreviousyear as part of a two-to-three year rotation away from potatoes. Field preparationusuallystartsintheautumn(fall)forproductioninthefollowingyear.Thesiteisirrigatedanddeep-ploughed to help ensure thedecomposition of organicmaterial from thepreviousyear’scropandtoproduceacold-freesoilwithidealmoistureforplantingin

Potato


Potato

earlyspring.Agrowermaychoosetoapplytherecommendedratesofphosphorousand potassium in the fall in order to encourage organic matter decomposition.

Preparation of Potato Pieces before Planting

At about one to two weeks before planting, store the tubers in a warm and lighted areasothebuds(eyes)willstarttosprout.Atonetotwodaysbeforeplanting,cutthelarger tubers into smaller pieces with a sharp and clean knife. Each piece should have atleastonetotwoeyes,andeachpieceshouldnotbelessthan5cmindiameter.Itisrecommendedtoleavethepiecestodryforafewhoursbeforeplantingsotheydonotrot.

SeedPhysiologicalAge

Aged or older seed tubers tend to produce plantswithmany stems that sproutanddevelop rapidly,but theplantsproduced fromolder tubersdieearly.Highstemnumbersusuallyresultinahighnumberoftubersperplant,whichreducestheaveragetuber size by reducing the amount of carbohydrate available to each tuber duringbulking.Early foliagedeathalsoshortensthebulkingperiodandreducestheoverallplantproductivity.Bycomparison,plantsfromyoungpotatoseedtubersbegintobulklaterthanthosefromolderseedtubers,whichmayshortenthegrowthperiodinsomeareas,especiallyinareaswithashortgrowingseason.

Planting Recommendation

Potato plants grow larger tubers and produce higher yieldwhen grown in rows(furrows)about90cmapartand15to20cmdeep.Ifthemarketdemandssmallersizetubersthenreducethespacingaccordingly.

Smaller tubers or tuber pieces are best when planted at about 30 cm apart with the cutsurfacesfacingdownwardandthebuds/eyesfacingupward.Asplantsstarttogrow,theyarehilledtocovertherootsandencouragetuberformation.

FertilityManagement

Developing healthy plants is necessary for maximum tuber growth. Nutrientdeficiencieslimitcanopygrowthandshortenthelifeoftheplants,resultinginreducedcarbohydrateproductionandtubergrowth.Similarly,excessiveuseoffertilizercausesnutrientimbalances,whichcandelayorslowtubergrowth.

Irrigation

Plantsrequireaconstantsupplyofmoisture.Allowingsoilmoisturetodropbelowcriticallevelsreducesorstopscanopyandtubergrowthduringthestressperiodandforseveraldaysthereafter.Thiseffectivelyshortensthetuberbulkingperiodandcanalsocauseavarietyofinternalbreakdownandexternaltuberdeformities.

Also,excessiveirrigationcanreducetubergrowthbyrestrictingnutrientuptakeandincreasingdiseasesusceptibility.

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Chapter 3

Weed Control

Alwayskeepyourpotatopatchweed-freeforbestresults.Potatoesshouldberotatedin the garden, never being grown in the same spot until there has been a three to four yearabsenceofpotatoes.

Harvesting and Storage

Reducinginjurytothetubersduringharvestwillminimizediseaseinfectionandlossofqualityinstorage.Itisimportanttoknowthattubersremainaliveeventhoughtheirvines have dried up. The two most important factors to keep tubers in fresh and firm physicalconditionaretemperatureandhumidity.Afterbeingremovedfromthegroundandplacedinstorage,tubersenteraperiodofdormancy,andunderproperconditionsoftemperatureandhumidity,theyremaindormantthroughoutthemarketingseason.Potatoesshouldbestoredandhandledinacool(7to10°C)environmentwith90to95percenthumidity.Everyeffortshouldalsobemadetominimizeexposureoftuberstolightthroughoutstorageandpost-harvesthandling.

POTATODISEASESPotatoesaresubjecttoseveralseriousdiseasesthatarecausedbyvarioustypesof

fungi, bacteria, viruses, andmycoplasmas.Diseases are generallymore severewhenpotatoesareproducedinmonoculture,whentheyareplantednearorfollowingothersolanaceous crops, when old infected seed pieces are used for planting, and when effective disease management programs are not developed and implemented. This chapterexaminesthemaindiseasesandpeststhataffectpotatoesinGeorgia.

PotatoDiseasesCausedbyFungiLate Blight

CausalAgent–Phytophthorainfestans.LateblightisaverycommondiseaseandisthemostdamagingpotatodiseaseinGeorgiaandmostothercountriesaroundtheworld.Lossescausedbylateblightarecomparableonlytodiseasescausedbyviruses.

Lateblightaffectsalltypesofpotatoesandinfectsallplantpartsexceptforflowers.

Disease Symptoms: Early symptoms of the disease appear on leaves as irregulardarkbrownspots.Thespotsexpandslowlyindryweatherandquicklyinwetweather.Theygrowinsize,oftenengulfingtheentire leaforapartofthe leaf.Cottony,whitemoldgrowthmaybeseenonthelowersurfaceandedgesoftheleafwhenhumidityishighandleavesarewet.Underwarmanddryconditions,thewhitemolddisappears,which indicates incidence of late blight. As the disease progresses, the entire plant will become covered with such spots and turn black.

Steminfection issimilar tothatof leaves. Itsearlysigns includespotsofdifferentsizes.Asthespotsspread,thestemsandbranchesdryout.Stemsturnblackanddieasspotsgirdlethem.Water is requiredfor infectionanddiseasedevelopmentsothediseaseismostsevereinrainyandwetweather. Itoccursquiteofteninthehighlandareas of Adjara.

Figure 3.1 Symptoms of late blight in potato. Author: Jean Ristaino


Potato

Tuberinfectionisverycommon.Tubersbecomeinfectedbyzoosporesofthefungusthatcanswimthroughsoilorsurfacewaterbymeansofflagellaorbyspores,whicharespread to tubers from leaves. As a result, the fungus infects the tuber skin, causing it to rot.

Newlyinfectedtubersdevelopspots.Tissuesofinfectedtubersslowlyturnbrown,developanunpleasantodourandrot,especiallyinstorage.

Control

• Removeabove-groundpartsofthepotatoplantfromthefieldfourtofivedaysbefore harvesting;

• Use effective crop rotation;

• Disinfectstoragefacilitiesandensureoptimalstorageconditions;

• Growplantsonridgesratherthanflatsurface;

• Disposeofwastepotatoesbydeepburial,feedingtoanimals,orburning.Donotputinpilesorapplytofieldsthatwillbeusedforanotherpotatocrop;

• Destroyvolunteerpotato,tomato,andsolanaceousplantsthatmayharbourthisfungus;

• Seed tubers must be free of late blight lesions to prevent introduction of this disease;

• Treat seed tubers with an appropriate fungicide prior to planting;

• Timelyandeffectiveuseoffoliarfungicidesduringthegrowingseasonisveryimportant for controlling this disease.

DryRotofPotatoTubers-Fusarium DryRot

Causal Agent – Fusarium solani. Thediseasemostlyoccursinstorageandrarelyinthefield.Itisfavouredbytemperaturesof10oto30ºCandatleast50percentrelativehumidity.Thediseasedevelopsrapidlyinstoragewhentemperaturesareabove3oC to 4ºC.

Thecausalfungussurvivesforlongperiodsoftimeinthesoil.Itcanalsosurviveindamagedtubersandinstoragefacilities.Thefunguspenetratesthetuberonlythroughwounds causedbymechanical injuryor through tissuesdamagedbyotherdiseasessuch as late blight and common scab. Plants emerging from infected tubers are weak andgrowslowly.

DiseaseSymptoms:Thediseaseusuallydevelops in storage three to fourmonthsafter harvest. However, tubers were probably infected long before the symptomsdeveloped.Thediseasedtissuesofthetubercontainwhitishwart-likeflakeswhichareactually fungusmycelia.Thefleshof the infectedareabecomes looseanddarkwithtime.Cavitiesfilledwithyellowishorbrownishmyceliadevelopinthefleshofinfectedtubers.Thetubereventuallydriesoutandbecomesmummified.

Control

• Maintenance of optimal storage conditions - temperature, humidity, air-movement, etc;

• Timelyremovalanddestructionofaffectedtubers;

Figure 3.2 Symptoms of fusarium dry rot on potatoe. Source: UNECE Organisation

Figure 3.3 Symptoms of potatoe canker. Source: Inspection Canada

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Chapter 3

• SeedlotswithevidenceofbruisingandFusariumdryrotshouldbetreatedwithaneffectivefungicide.Tubersshouldonlybeharvestedfromdeadvines.Removetheabove-groundpartsofthepotatoplantfromthefieldfourtofivedaysbeforeharvesting;

• Croprotationcanbeeffective;however,rotationsneedtobelong(severalyears);

• Selectionanduseofclean(diseasefree)plantingmaterial.Preventanyformofmechanicaldamage(wounding)tothetubersduringharvestandstorage.

PotatoCanker,BlackScaborWartDisease

CausalAgent–Synchithriumendobioticum.The disease is so serious and destructive thatimmediatecontrolmeasuresarerequired.Cankerorblackscabaffectsallpartsofthepotato,especiallythetuber.Itoccurslesscommonlyontheabovegroundpartsofthe plant.

DiseaseSymptoms:Theexternalsymptomsofthediseasearesimilarinmostcases:The infected area forms scab-like lesions of various sizes which are initially small,approximately the size of a corn kernel. Later they grow to form gall-like growthsthatcanbecomelargerthanthetubers.Atfirsttheyounggalliswhiteandlookslikeacauliflowerheadbutthenchanges itscolourandturnscompletelyblack.This isanindicationof thetuber tissuedisintegration.Thegallfinally rotsandtheentire tuberdecays.

Similargallsandscab-likelesionscanformontheabovegroundpartsoftheplant.Atthistime,thepartsoftheplantabovetheinfectedareadryoutandtheentireplantdies.

Control

• Select and use resistant varieties when possible;

• Crop rotationcanbeeffective;however, rotationsmustbe fairly long (severalyears);

• Disinfectionofpotatotubers.

PowderyScab

Causal Agent – Spongosporasub terranean. Powdery scab is causedbya fungus-like organism that infects tubers and roots through natural openings. The source of the infection is plant debris and infected tubers where the spores causing this disease are found.Sporesofthisorganismcansurviveinsoilforoversixyears.Infectionisfavoredincool(15oto20oC)andmoistsoils.InfectioncanoccuroverawiderangeofsoilpH.

DiseaseSymptoms:Thediseaseaffectspotatotubers,butrarelyrootsandstems.Itmostlyoccursonthesurfaceofthetuberandisnottypicallyspreaddeepinthetissue.

Smallpimple-like structures appearunder theepidermisof young tubers.As thediseaseprogresses,theygrowlargerandshowuponthetubersurface.Theepidermisthenburstsproducingsunkenscab-likelesionswithbrownpowder.

As the rootsbecome infected, theydevelopsmall scabswithaflatpart (thepartattachedtotheroot).Scabbedtubersusuallyrotbeforeharvest.

Figure 3.4 Symptoms of potato powdery scab. Source: Wikipedia


Potato

Control

• Treat seed pieces with an appropriate fungicide prior to planting;

• Crop rotation (avoidgrowingpotatoes inscab-infectedareas for three to fouryears);

• Select seed potato free of powdery scab; harvesting should be done in dryweather;

• Plant potatoes on ridges at least 30 cm high;

• Selectplantingsitesthatarewell-drainedanddonothaveahistoryofpowderyscab.Manurefromanimalsfedpotatoesmaycontainpowderyscabspores.Donotapplymanuretofieldsusedtogrowpotatoes.

EarlyBlight

Causal Agent – Alternaria solani. Thediseasedevelopsatatemperaturerangeof22o

to24ºCbutitcanalsodevelopatlowertemperaturesabove10ºC.

Thecausalfungusoverwintersinplantrefuse(debris)asmyceliaorconidia.

Plants weakened by weather or soil conditions unfavourable to potato growtharemoresusceptibletoearlyblight.Thediseasefavoursdryandhotweather, lackofmoisture,lackofnitrogenandpotassiuminthesoil,andexcessamountsofphosphorus-containing fertilizers.

Disease Symptoms: The disease first appears during the budding period and developsthroughouttheentiresummer.Thefungusmostlyaffectsleaves;sometimesitaffectsstems,andrarelyaffectstubers.

Drybrownspotsfirst appearon lower leaveswith concentric ringson theupperside of the spots. Leaf spotting then spreads upward. The spots also form on stems and sprouts if conditions are favourable for the disease development. As a result, the upper partoftheplantmaydryoutanddie.Dried,deadleavesremainattachedtothestem.

Tubersare typically infectedduringharvestonthesoil surfaceorbycoming intocontactwithsporeson thestemand leaves. Infectionof tubersonlyoccurs throughwoundssuchasmechanicalinjury.Irregularlesionsontubers(upto2cmindiameter)aresunkenandslightlydarkerthanhealthyskin.Abrowntoblack,corkydryrotmaypenetrateupto1cmintotuberflesh.Infectedtubersrotinstorage.

Control

• Removetheabove-groundpartsoftheplantfourtofivedaysbeforeharvesting;

• Crop rotation with small grains, corn, or legumes, growing potatoes or tomatoes onlyeverythreetofouryears;

• Plowfieldstodeeplyburyallplantrefuse;

• Seedtubersmustbefreeofearlyblightlesions;

• Remove volunteer potatoes and tomatoes from within and near the planting;

• Disinfectstoragefacilitiesandensureoptimalstorageconditions;

• Timelyandeffectiveuseoffoliarfungicidesduringthegrowingseasonisveryimportant for controlling this disease.

Figure 3.5 Symptoms of early blight in potato leaf. Author: Tom Leroy

Figure 3.7 Symptoms of rhizoctonia on potato tuber. Source: Michigan University

Figure 3.6 Symptoms of cercospora leaf blotch. Author: Bob Souvestre

41

Chapter 3

Cercospora Leaf Blotch

Causal Agent – Cercospora concors. The causal agent overwinters in plant residue.

DiseaseSymptoms:Thediseasefirstappearsonlowerleavesassmall(2mm),paleyellowishspots.Thespotsthenexpand insizeupto2-3cmandmaybesurroundedby a thin yellow band of tissue (halo).The infected tissue cannot initially be clearlydistinguishedfromthehealthytissue.Theinfectedtissuelaterfallsintodecayandthedifferencebecomesmoreevident.Thespotsareeventuallycoveredwith thinpurpleflakes/specks and dry out. On the underside of spots, a violet grey layer of fungusgrowthmaydevelop

Control

• Remove theabove-groundpartsof thepotato from the landplot four tofivedaysbeforeharvesting;

• Implementeffectivepracticesinpotatocultivation;

• Disinfectstoragefacilitiesandensureoptimalstorageconditions.

• Timelyandeffectiveuseoffoliarfungicides.

Rhizoctonia

Causal Agent – Rhizoctonia solani. Thisdiseaseismostsevereduringrainysprings.Disease development and spread is favoured by poor cultural practices (when thetuber isplantedtoodeep)aswellasbyplanting insandyandslightlyacidsoils.Theoptimaltemperatureforthediseaseis12oto15ºC.Thefungusoverwintersassclerotiaontubersorasmyceliaorsclerotiainthesoilwhereitsurvivesforatleastthreetofouryears.Infectedseedtubersarethemainsourceofinfectionforemergingsprouts,whileundergroundstemsandstolonsareattackedbyfungalmyceliaandsclerotiainthesoil.

Inadditiontothepotato,thisfungusaffectsothervegetables(tomatoes,cucurbits,beetroot)andweeds(sowthistle,horsetail,fatten,etc.).

DiseaseSymptoms: The disease is found on tubers and sprouts. Tubers form black velvetyspots.Thespotsposenodangertothealreadydevelopedtuberbutcanseriouslyaffectyoungtubersandsprouts.Whenyoungtubersgetinfected,theydonotreceivea sufficient amount of starch.The tuber then becomes transparent andwatery andeventuallydriesoutleavingonlytheskin.Thesamesymptomsarefoundinlatetubers.Thediseasecanspreadtostems.Greyishmyceliamaygirdlethestem.Iftheupperpartoftheplantisinfected,stemsdevelopslowly,weaken,turnblackandthendie.Thiscanresultinanunevenstandofplants.Ifthestemdoesnotdryout,itsgrowthslowsdownand top leaves along the mid vein become torn, inhibiting the tuber development. A black spot appears on the young stemwhich gradually expands and surrounds thestem.Asa result, thestembreaksandmayproducenewsproutsbelowthepointofthebreakwhichwillalsogetinfectedandbreak.Mildlyinfectedstemsmaystillemergefromthesoilbutwilleventuallydie.Suchstemsdevelopabove-groundtubers.

Control

• Chitting;

• Crop rotation with corn, grasses, and cereal grains will reduce pathogen populationsinsoil.Donotplantpotatoforthreetofiveyears,ifdiseasehasbeensevere;

Figure 3.8 Symptoms of potato virus X on leaves. Source: CIP potato


Potato

• Selectionanduseofdisease-freeplantingmaterial.Seedpiecesmustbefreeofblack particles of Rhizoctonia on the skin surface;

• Treat tubers with an appropriate fungicide dust prior to planting;

• Promote rapid emergence of sprouts to suppress this disease. Avoid planting inheavy,poorly-drainedsoils.Plantwhensoilisabove15°C.Coverseedtuberswith no more than 3cm of soil, then after plants emerge, build up hills during cultivation;

• Harvest tubers promptly after vines are dead to avoid development of blackfungal particles on tuber skin.

PotatoDiseasesCausedbyVirusThereareseveralpotatodiseasesthatarecausedbyvirus.Themostimportantand

commondiseases include:PotatovirusX (PVX); aucubamosaic virus (PAMV);potatospindletubervirus(PSTV);potatovirusS(PVS;)andpotatovirusy(PVy).

PotatoVirusX(PVX)

CausalAgent–PotatovirusX.Thediseasereducesyieldby10percent,andby45percentinthecaseofmosaic.Thediseaseisspreadonalandplotbycontactbetweenplants.

TherearemanysolanaceaeandleguminouscropswhichfeedtheXvirus.Weedscanalso be infected.

DiseaseSymptoms:Paleyellowishspots intermingledwithgreenspotsdevelopon the surface giving the leaf a mosaic look. Leaves are more mottled in cool weather than inwarmweather. Additional symptoms include a general chlorosis and slowgrowth. Somevarietiesmaydevelopblacknecrotic spotson leaves.There are alsovarietieswhere symptomsdisappear as theplantgrows, and thediseasebecomeslatent.

PotatoAucubaMosaicVirus(PAMV)

Causal Agent – Potato virus M. Thediseaseistransmittedbyinfectedplantsandthe peach aphid (Myzuspersicae).Itcausesyieldlossesofupto30to40percent.

DiseaseSymptoms:Thetypeandintensityofthesymptomsinpotatoplantsdependonthestrainofvirusandthecultivarofpotato.Thetwomaintypesofsymptomare:(1)brightyellowspotsonthelowerleaves,latercoalescingtoformlargeyelloworwhitishpatches; (2) necrotic spots, often leading to systemicor topnecrosis. Some infectedplantsdonotshowfoliagesymptoms,especiallyduring thesecondandsubsequentyearsof infectionandwhengrowingunderglass.Duringstoragethetubersofmanycultivarsdevelopnecrosis in the cortex andpith visibleon the surfaceas irregularlyshaped,brownpatchesorsunkendrybrownareas.

Figure 3.9 Symptoms of aucuba mosaic virus on leaves. Source: Wikipedia en France

Figure 3.12 Symptoms of potato virus M on leaves. Source: Ibric org.

Figure 3.11 Symptoms of potato virus Y on leaves. Source: WikiGardener

Figure 3.10 Symptoms of potato virus S on leaves. Source: AHDB

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Chapter 3

PotatoVirusS(PVS)

Causal Agent – Potato virus S. Thisvirusalwaysoccurs incombinationwithotherviruses.ItinfectsplantsintheAsteraceae (Compositae)family,andthemintfamily.

DiseaseSymptoms:Compared to unaffected plants, leaves of infected plants are of apalecolour,withthetipofyoungplantsbendingdown.Theplantlosestissuetone(turgor)andbeginstowilt.CertainpotatovarietiesinfectedwithSvirushavealmostthesamesymptomsasvirusX.

LeafDropStreakandRugoseMosaicofPotatoesPotatovirusy(PVy)

Causal Agent – Potato virus y. The disease may cause yield losses of 30 to 70percent.Thelossdependsonthepotatovariety,thespreadofthediseaseandgrowingconditions.Infectedplantsmaydieinthesecondhalfofthegrowingseason.Severalrecombinant strains of PVy are reported PVy (O), PVy (NO), PVy (O), PVy (N-Wilga).RecombinantPVy(O)isthemostwidespreadstrainamongthethreePVystrains.Thediseaseistransmittedbyaphidsandasaresultoftubercuttingpriortoplanting.

Disease Symptoms: Several strainsof PVyhavebeen identified thatdifferby thesymptomstheycauseinpotatoesandtobacco.PVyO is the common strain, and causes mosaicsymptoms.PVyC causesstipplestreak.PVyN, the necrotic strain,generallycausesmildfoliagesymptoms,but necrosis in the leaves of susceptible potato varieties.

PotatoLeafroll-PotatoVirusM(PVM)

Causal Agent – Potato virus M. Thediseasecausesyieldlossesupto25to40percentandreducesthestarchcontentintubersby2to3percent.

Thediseaseistransmittedbymechanicalcontact,throughaphidsandbugs.

DiseaseSymptoms:Wrinkledupperleaveswithmosaicsymptomsandwavyedges.Thesymptomsareprominentduringthebuddingperiod,butdisappearslowlybytheendofthegrowingseason.Inmostcases,thevirusislatentandoccursincombinationwithX,SandBviruses.

Control

• Testkitsorlabtestsareoftenrequiredtoidentifyplantviruses;

• Planting seed potatoes free of viruses is the most important management strategy;

• Cleanandproperlysanitizefieldandhandlingequipmentandstorageareas;

• Properlydisposeofwastepotatoesandeliminatevolunteerpotatoplants;

• Manageinsectsandnematodesthatmaycarryviruses;

• If possible, remove virus-infected plants when they are found in productionfields.


Potato

PotatoDiseasesCausedbyBacteriaOf other bacterial diseases, blackleg causes themost serious damage to potato

crops, resulting in a bacterial ring rot of potatoes, and bacterial rot of potato tubers resultsinaverydestructivewetrot.

Blackleg

CausalAgent –Pectobacteriumphytophthorum.Thedisease affectsboth above-groundandundergroundplantpartsatanystageoftheirdevelopment.Thebacteriathat causeblackleg are rod-shape.They are coveredwith flagellawhichmake themmobile.Theycanswiminafilmofwaterorinfreewaterinthesoil.Thebacteriaoverwinteronplantrefuse(debris)insoilandoninfectedtubers.Thebacteriacansurvivein soil and plant debris above ground for at least two years. The bacteriamay alsoaffectotherplants,inadditiontothepotato,whichincludesmanyspeciesofweed.Theoptimumtemperatureforitsdiseasedevelopmentandspreadis21oto26ºC,butitcandevelopatawiderangeoftemperature(2oto32ºC).Thebacteriacanalsobespreadbymaggots.

DiseaseSymptoms:Symptomsdevelopneartherootcollarordirectlyontherootcollar. At this time, the infected tissue forms small blackish spots which graduallyenlarge and coalesce. The spots then cover the entire root collar, the stem turns red and theplantcollapses.Beforeitcollapses,itsleavesturnyellowandtheplantvisiblystopsgrowing.

Tubers are infected if the disease develops late. At this time, the centre of the tuber rots, disintegrates and turns into a cavity.These symptomsmaynotbevisible if thetuberinfectionismild.Infectedtubersproduceaninfectedplant.

Control

• Sanitation–Collectanduseonlydiseasefreetubersforplanting;

• Chitting;

• Weed control;

• Croprotationforatleasttwotothreeyearsawayfrompotatoes.

Bacterial Soft Rot

CausalAgents–Erwinia,Corynebacterium,Clostridium.The disease causes the tuber torot.Tubersmaygetinfectedduringtheperiodpriortoharvestwhenthebacteriagetsinto the tuber from stolons or from infected seed pieces (i.e. the infected tuber produces infectedplants), aswell as throughamechanical injuryduringharvest.Thebacteriacanalsoinfecttubertissuesthataredamagedbyotherdiseasessuchaspotatoscab,lateblight,andblackleg.Theycanalsoenterthroughwoundscausedbycertaininsectpests.Thediseaseoccursmostly instorage.Tuberswithnomechanical injuriesrarelyget infected.

DiseaseSymptoms:The tuberbecomessoftwithfluiddraining fromthe infectedtissue. The tuber tissue disintegrates. The tuber skin does not disintegrate, but its content iscompletelydecayedintoaslimymass.Therottingprocessreleasesunpleasantodours.

Figure 3.13 Symptoms of blackleg on potato tuber. Source: University of Moscow

Figure 3.14 Symptoms of bacterial soft rot. Author: Don Edwards

45

Chapter 3

Control

• Croprotationisimportant.Ifthediseaseissevere,growingofpotatoesshouldbeavoidedforatleastafterfourtofiveyearsininfestedfields;

• Maintenance of optimal storage conditions;• Timelydisposalanddestructionofaffectedtubers;• Control of pests and fungal diseases prior to harvest and in storage with

appropriate insecticides and fungicides.

PhysiologicalDisordersPhysiologicaldisordersaredisease-likesymptomsthatarecausedbynon-biological

orabioticfactors,suchasnutritionaldeficiencies,fluctuationofsoilmoisture,changesintemperature, and other abiotic factors. Abiotic factors affecting potato include internal heat necrosis, tuber cracking, hollow heart, and black heart.

InternalHeatNecrosisAlso known as internal brown spot rust spot, internal browning, and internal brown

fleck.Thisdisorderiscausedbyelevatedsoiltemperaturesduringthelatterstagesoftubergrowthanddevelopment.Lowlevelsofcalciummayalsoplayanimportantrolein the occurrence of the disorder. Several studies have found a link between reduced calcium levels in tubers and increase in the incidence of internal heat necrosis.

Thenecrosisappearsaslighttan,darkyellowtoreddishbrownflecksorspecks,thesemaybedarkbrownorblackinthemostseverecases.Theyresemblethenecrosisseenwithchillinginjury.Flecksusuallyclusternearthecentretowardthebudendandcanappearsimilartoblackheart.Theflecksarefirm,thereisnobreakdownorrot.Vasculartissueisusuallynotaffectedbutinsomecasesflecksmaybeconfinedtothevasculartissue at the bud end.

Intubers,necroticareasaremostlyfoundinandaroundthevascularbundle,usuallycoalescingandradiatingtowardsthecentre(pith).Thesymptomsaremoreprevalentatthebud(apical)endthanatthestemendofthetuber.

Theexteriorofthetuberinsomevarietiesmayexhibitsymptomsalongwithinternalnecrosis,but this isnot always the case, and somevarieties, likeAtlantic,mayneverexhibitvisibleexteriorsymptom.

Preventive methods:Nutrientbalanceshouldbeproperlymanagedtoreduceplantstressearly in the season,particularlyduring rapidgrowthanddevelopment.This isespeciallytrueforcalcium,whichshouldbesuppliedatthedepthatwhichrootingandtuberdevelopmentoccur. Preventing shallow tubers frombeingexposedalsohelpspreventIHNoccurrence,whileoptimalirrigationamountsandincreasedsoilcovercanreduceexposureofshallowtuberstoexcesstemperatures.Ifirrigationisbeingused,soilmoistureshouldbemonitoredcarefullysothatfavourableconditionsarenotprovidedfor other disorders or diseases.

Tuber Cracking

Tubercrackingcanbecausedbyseveral factors including internalpressure,virusinfection,andmechanical injury.Growthcracksfrominternalpressureoccurbecause

Figure 3.15 Symptoms of potato heat necrosis. Source: Potato Inspection Canada


Potato

ofrapidtubergrowth.Potatocultivarsdifferintheirsusceptibilitytothistypeofcracking.Cracks are more severe when turgid tubers on vigorous vines are harvested from cold soil.

Preventive methods: Avoid over irrigation following a persistent drought. Permit soil towarmbeforeharvestingtubers.Handlefreshlyharvestedtuberswithgreatcare.Curetubersatappropriatetemperatureandhumidity (about15°Cand95percentrelativehumidityforoneweek)beforetransferringtubersincoldstorage.

Hollow Heart

Hollowheartisaconditionbroughtaboutbytoorapidorirregulargrowth.Itoftenoccursduringwetseasons inpotatoesgrown invery fertileorheavily irrigatedsoils.Hollowheartconsistsofmoreorlessirregularcavitiesofvaryingsizeswithinthetuberandisusuallylinedwithlight-browntobrowndeadtissue.Thisdefectisusuallyfound,butnotalways,inlarge,rough,misshapenpotatoes.

Hollowheart starts as a brown centre,which is characterized as a small 0.5 to 3centimetresindiameter,brown,circularorelliptic,opaqueareawithadiffuseborderalongthelongitudinaltuberaxis.Inroundtoovaltubers,itisusuallyatthetuberscentre;with longoroblong tubers, theremaybe twobrownareas,oneateachend.Brownareasaredistinctbuthaveasmooth,gradualchangetounaffectedtissue.Dependingonthespeedofgrowthresumptionafterstress,browncentremayormaynotdevelopintohollowheart.Hollowheartappearsasalensorstar-shaped,irregularcavityinthecentre of round tubers such as Atlantic, or at either or both stem and bud ends of long tubers.Theinternalwallsarewhitetotan.Thecavityislargerwithlargertubersandismostlyseeninverylargetubers.Norotisassociatedwiththedisorder.

Preventive methods:Dependingonlocalconditions,hollowheartcanbedifficulttoprevent,butfollowingaconsistentwateringschedule,applyingadeeplayerofmulch,and dividing fertilizer into several small applications can help protect the crop.

Planting potatoes too earlymay play a part in hollow heart. If hollow heart is aproblem,waitinguntilthesoilhasreached15oCmayhelppreventsuddengrowth.Alayerofblackplasticcanbeusedtowarmthesoilartificially ifthegrowingseasonisshort andpotatoesmust reachmaturity early. Also, planting larger seedpieces thathaven’tbeensignificantlyagedseemstobeprotectiveagainsthollowheartduetoanincreased number of stems per seed piece.

Preventive methods:

• Plant closer;

• Use larger, less aged, large seed pieces;

• Establish good plant stands;

• Avoid plant skips;

• Applypotassium;

• Schedule irrigation for constant and uniform tuber growth.

Black Heart

Blackheart appears as an internal browning to blacking of the centre tissue of thetuber.Usually,thereisnocavity.Patternisirregularbutmarginsarewelldefined.

Figure 3.16 Symptoms of hollow heart in potato. Source: Gardening Know How

Figure 3.17 Symptoms of potato black heart. Source: Northern Dacota State University

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Affectedtissueisfirm,notsoftaswithleak,but,whentemperatureisgreaterthan18oC, itmayturnsoftandinky.Itiscausedbyanoxygendeficiencyatthecentreofthetuber.Oxygendeprivationresultsinasphyxiation,lossofrespiration,anddeathofcells.Thedisorder can develop around harvest, in storage and in transit.

Preventive methods: Avoid any pre-harvest, storage, and transit condition thatpreventsoxygen from reaching the tuber centre.Also avoidpoor ventilation,water-logging, longexposuretohighfieldtemperatures (higher than35oC)beforeharvest,andprolongedstorageatlowtemperatures(lowerthan2oC).Tubersusedasseedcanhavelowervigourandstandbecauseoflowtuberstarchthatmaynotbesufficienttosupport plant emergence.

Misshapen tubers

Misshapentubers (calledsecondgrowth) result fromunevengrowingconditions,including sporadicwatering and high temperatures. A consistently large number ofmisshapen tubersover several seasons indicate thevariety isprobablynot suited tothat environment

Preventive methods: Avoid irregular irrigation. Avoid over fertilizing, especiallyduring the bulking period or when the plants are in bloom. Use varieties less susceptible tomisshaping.Useridgesforplantinginsteadofflatsurfaces.Avoidsoilcompaction

Physiologicalleafrollsofpotatoandtomato

Physiological leaf rollstartswithupwardcuppingat the leafmargins followedbyinward rolling of the leaves. Lower leaves are affected first, and can sometimes recover if environmental conditions and cultural factors are adjusted to reduce stress. If theconditionsfavoringleafrollareprolonged,affectedleavesmaynotrecover. Inseverecases,wholeplantscanbeaffected.Ifenvironmentalconditionsandculturalfactorsareadjustedafterprolongedleafrolling,newgrowththatdevelopsmaynotexhibitleafrollsymptoms.

The severity of leaf roll appears to be cultivar dependent. High production-potentialcultivarstendtobemostsusceptible.Highlyvigorouscultivarsofpotatoandindeterminate cultivars of tomato were reported to be more sensitive to this disorder thanlessvigorousanddeterminatecultivars.Insomecases,theconditionisbelievedtooccurmostcommonlywhenplantsarestakedandprunedduringdrysoilconditions.Inothercases,causeslistedincludegrowinghigh-producingcultivarsunderhighnitrogenfertilityprograms,phosphatedeficiency,orextendeddryperiods.Also,thedisorderhasbeen attributed in some areas to excess soilmoisture coupledwithprolongedhightemperatures.

Preventive methods:Somemanagementstrategiesrecommendedforphysiologicalleafrollincludeplantinglowvigoranddeterminatecultivars.Plantinwell-drainedsoandmaintainuniform,adequatesoilmoisture(~2.5cmperweekduringthegrowingseason,dependingontheareaofproduction).Becarefulnottoover-fertilize,especiallywith nitrogen fertilizers providing adequate phosphorus fertilizer. Avoiding severepruning, and if possible, maintain temperatures below 35oC by using shading orevaporative cooling.

Figure 3.18 Symptoms of misshapen potato tubers. Source: Fried to Fublog

Figure 3.19 Symptoms of physiological leafroll of potato. Source: Potato Inspection Canada


Cucumber is a member of the cucurbitaceae family. This family includes manyimportant vegetables like watermelon, muskmelon, pumpkin and gourd. They areallwarm-seasonannualcrops.Cucumberhasa longhistoryofcultivation forhumanconsumption and it is a popular vegetable throughout the world. Fruits are either eaten fresh in salads or processed into relish, pickled whole, or sliced.

The crop is very susceptible to serious losses from soil-borne and foliar diseases.Productionvolumesareusually40to50percentlowerduringthehotsummermonthswhen diseases are more prevalent than in milder and drier summers.

PlantGrowthandFruitSet

Cucumberisanannualdeep-rooted(about1meterdeep)planwithtendrilsandhairyleaves.Theplantsmayhaveindeterminateordeterminatecompactplanthabits.The compact growth habit cultivars consist of plants with shorter internode length than plants that are indeterminate.Determinate cultivars aremore suitable for fieldproduction, while indeterminate cultivars are more suitable for greenhouse and high tunnelproduction.Optimumgrowthoccursbetween20°to25°,withsignificantgrowthreductionoccurringbelow16°Candabove30°C.

Threemajorfloweringhabitsexistamongavailablecucumbercultivars.Themostwidely grown commercial cultivars are monoecious, producing separate male andfemaleflowersonthesameplant.Theothertwoaregynoeciousor“all-female”cultivarsproducingonly femaleflowers(up to adozen timesmore femaleflowers than thoseobtainedinmonoeciouscultivars)ortheso-called“PF”hybridsproducingpredominantlyfemaleflowersandasmallnumberofmaleflowers.ThemaleflowersproducedonPFhybridsarenotsufficient toproduceaneconomicalcropandsopollinatorplantsareusually included toinsure sufficient fertilization. In themonoeciouscultivars, thefirstflowers are mainly staminateor ‘male’ followed by pistillate or ‘female’ flowers, fromwhich fruits are formed.

In addition to genetics, production ofmale and/or female flowers is affected byseveral other factors including plant density, plants tress, temperature, and lightintensity.Forexample,reducedratesoffemalefloweringynoeciouscultivarsmayresultfromexposuretostresscausedbyhighplantpopulationdensities,insectattack,winddamage,andcombinationsoflowlightintensityandhighambienttemperatures.SomecommercialgrowersintheUS,spraygynoeciousplants,atthetwotofourleafstage,witharegisteredgrowthregulatorcalledethephon(2-chloroethylphosphonicacid)at125-250ppmtoincreaseformationoffemaleflowers.

Manycultivarsgrowninhightunnelsandgreenhouses(liketheEuropeantypes)areparthenocarpic(haveabortedseeds).Parthenocarpicvarietiesrequirenopollinationtosetfruits.Infact,pollinationofthesecultivarsmaycauseanoff-shapedfruitappearance.

Cucumbersthatproducemaleandfemaleflowersonthesameplant(monoecious)are dependent uponhoneybees for pollination. It is recommended that four to fivehives should be used per hectare.

SoilRequirement

Cucumberplantsareadaptedtoawidevarietyofsoil typeswithgooddrainageand adequate water-holding capacity. Cucumbers don’t perform well on acid soils

Cucumber

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Chapter 4

but dowell under slightly acidic conditions (pH 5.5 to 7.0). It is recommended thatif soilpH is lower than5.5, agrower shouldapplyabout2.5 tonsperhectare (or22kg per m2) of agricultural lime at about 8 to 12 weeks before planting. However,some soilsmay require considerablymore lime. It is suggested that liming and useof nitrate-nitrogen fertilizer helps to reduce incidence of fusarium wilt in the field.However, the availability of somemicronutrients may be reduced at pH above 6.5.

Fertilizers Recommendation

Cucumber’snutritionprogramshouldbe tuned toachievemaximumyields andoptimummarketquality.Forexampleinsufficientpotassiumwillresultinmisshapenfruit or “bottlenecks”, and low nitrogen restricts growth, modifies the length-to-diameterratio, reduces set and color development of the fruits.

It is suggested that 50% of the recommended fertilizer rate need to be bandedabout8cmbelowtheseedsatplantingandtheremaining50%issidedressedat30daysafterplanting.

Crop Rotation

Proper crop rotation is essential in cucumbers in order to reduce potential problems fromdiseases,nematodes, andherbicides carryover. It ishiglydiscouraged togrowcucumbers on lands that have been plantedwith any other cucurbit crops such aswatermelons, cantaloupes, pumpkins, squash, etc, within the previous three years.Proper rotation with non-cucurbit crops will help prevent potential problems fromcarryoverofdiseasesonplantmaterial.Rotationwithcropsthatdiscouragenematodeisalsobeneficial.Agoodcroprotationprogramcould includecabbage,corn, ryeorothersmallgrains.Otherwell-fertilizedvegetablecropsnotinthecucurbitfamily,suchasfresh-markettomatoesorpeppers,aresuggestedtouseinacucumberrotation.

Irrigation

Cucumber plants require constant supply of water to produce high-qualityfruits and high yield. Periods of growth when the plants are most susceptible toirrigation deficits include seed germination, flowering, and fruit enlargement.The frequency of irrigation is largely dependent on soil type and weatherconditions. In general, for sandy soils under dry weather, the fields should beirrigatedat leasteveryotherday ifnotmoreoftenatarateof2.5to5cmperweek.

Weed Control

Use an integrated approach to effectively manage weeds in cucumber fields.Cultural practices for weed control include shallow cultivation, plowing, disking, hoeing, croprotation, cover cropping, living mulches, organic or plastic mulches, and herbicides. A pre-emergence herbicide application and two hoeings after plantingare sufficient to controlweeds inplots thathave lowweed seed stocks.Oneor twocultivationswhilecucumberplantsarestillyoungalsomayprovideacceptableweedcontrol. The two hoeings could be substituted with a post-emergence herbicide toachievesimilareffectiveness inweedcontrol.Alsogrowingcucumbersusingplastic-mulch is an effective method of controlling weeds.


Cucumber

CUCUMBERDISEASESHigh water content in cucumber is a factor that contributes to its being infected

withseveral importantdiseasescausedby fungi,bacteriaandviruses.Mostdiseasesrequire water to infect the plant and develop; therefore, diseases are most severewhenconditionsarewetduringperiodsoffrequentfog,dew,rainfallandhighrelativehumidity.Themaindiseasesofcucumberthatarecausedby fungi include:powderymildew;Sclerotiniarot;anthracnose;gummystemblight;Cladosporiumfruitandleafspot;downymildew;Alternariosis(Alternarialeafspot);targetspot;Fusariumwilt;blackrootrot;andgraymold.

The most serious diseases caused by viruses include cucumber mosaic virusandcucumbergreenmottlemosaicvirus.Importantdiseasescausedbybacteriaincludebacterial soft rot and wilt and bacterial wilt.

CucumberDiseasesCausedbyFungiPowderyMildew

Causalagents–Erysiphecichoracearumf.cucurbitacearum,Sphaerothecafuliginea.f. cucumis. The fungus can overwinter in plant debris from infected plants and can infect severalotherplantsinthecucurbitaceaefamilyincludingpumpkin,squash,cantaloupeand watermelon. The fungus can also infect certain weeds such as L Sonchus and plant ago.Diseaseseverityincreasesduringdryandhotweatherconditionswithhighrelativehumidity.Thefungusdoesnotrequirefreewatertoinfecttheplant,insteadthefungusrequires high relative humidity to infect. Rapid changes of temperature and relativehumidityalsocontributetodiseasedevelopment.Thediseaseprogressesrapidlywhenthereisnorainfallbutdewandhighrelativehumidityexists.Unlikemostotherdiseasescaused by fungi, rain fall can actually inhibit the development of powderymildew.The incubation period from infection to symptomdevelopment is four to five days;therefore,thediseasecandevelopveryrapidly.Especiallywhenventilationandlightingispoor,powderymildewcanbeveryseriousinthegreenhouse.

DiseaseSymptoms:Thefungi causingpowderymildewareobligateparasitesandcan only develop on living plants. Erysipheci choracearum creates a white powderygrowth of fungus mycelium on infected leaves, while the powdery growth createdbySphaerotheca fuligineaispink.Thediseasecandamagethecropatanystageofitsdevelopment, both in the field and in greenhouses. Disease symptoms first appearon the upper side of the leaf. At this time, singular spots appear on the leaf, as white mildew(fungusgrowth).Later,similarspotsappearonthebottomsideoftheleaf.Inthe case of severe infection, spots grow in size, merge and cover the entire leaf. White powderygrowthmayalsodeveloponthestemsandfruitstalks (petioles).Damagedleaves yellowdry andeventuallydie. Plantdevelopmentdecreases andproductivitydiminishes.Diseasedplantsformsmallanddryfruit.

Control

• Useculturalpracticesthatavoidexcessivesucculenceandplantgrowth,over-crowdingofplants,shading,overwatering,orexcelfertilization,especiallywithnitrogen.

• Avoid making new planting of vine crops in the vicinity of older plantings,especiallyifmildewisalreadypresent.

Figure 4.1 Symptoms of powdery mildew in cucumber. Source: Vegalab

Figure 4.2 Symptoms of sclerotinia rot. Source: Sclerotinia Organisation

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Chapter 4

• Destroyweedsnearorinthefieldplantingandneargreenhouse.

• Sanitation–Removeanddestroyplantdebrisfromthefieldorgreenhouse.

• Observeoptimal timeperiods forgrowingand transplantingseedlings. In thegreenhouse, it isnecessary toobservean intervalofno less thanthreeweeksbetweenfallandwinter-springplantings.

• Properly time applicationof effective fungicides are important for controllingthis disease.

SclerotiniaRot(whiterot)

Causal agent – Sclerotinialibertiana. The pathogen has a very wide host rangeinfecting over 300 species of plants. Plants can be damaged at any stage of theirdevelopment. All parts of the plant are susceptible. This disease can kill newlyemerged plants, cause wilt on mature plants and rot the fruit. The fungus produces survival structures called sclerotic at that can survive for long periods of time in the soil.Wetconditionswithhighhumidityandrelativelylowtemperaturesfavordiseasedevelopment and spread. The disease can be a serious problem in greenhouses as well as in the field.

Disease Symptoms: Disease symptoms are often observed on the part of theplant locatednearthestemroot.Smallwet(watersoaked)spots initiallyappear,onwhichwhitemycelia later develop.Thediseasegradually spreads toupper tiers oftheplant.Damagecausedbythispathogentothestem,branchingpointsandleavesis especially severe. Under conditions of high relative humidity, thewhitemyceliadevelopsquickly.

Asaresultofdevelopmentofwhiterotontheplant,affectedpartsdieslowly,whichfinallycausescompletedeathoftheplant.Firstsymptomsofthediseaseappearonfruitsets.Later,symptomscanbeobservedatallstagesoffruitdevelopment.Itshouldbenotedthatthepathogenpenetratesfruitmostfrequentlythroughmechanicaldamage.Duringthefirststagesofdiseasedevelopment,damagedareasoftheplantdevelopadirtygreencolor,becomewet(watersoaked)andsoft.Asthediseasespreads,infectedfruits become coveredwith a dense layer ofwhitemycelia. Eventually, black bodies(sclerotia),developamongthemycelia.Thesearethelong-termsurvivalstructuresofthe fungus. Under humid weather conditions, diseased fruits rot and collapse. Under conditionsoflowrelativehumidity,diseasedfruitmummifyandcanbecomecompletelycovered with sclerotia. Mummified fruits canremain on the plant for a long time. Plant leaves become diseased as a result of contact with diseased plant remains or diseased partsoftheplant.Infectedleavesinitiallydevelopwetspots.Underclimaticconditionsfavorablefordiseasedevelopment, fungusmyceliaspreadsquicklytoallpartsoftheleaf, which then tears, deforms, dries up, and dies.

Control

• Because of the long term survival structures of the fungus (sclerotia), croprotation is general not considered to be effective.

• Goodagriculturalpracticesandsanitary-hygienicmeasures,includingcleaningagriculturalequipmentbeforeenteringnewfields,arerecommended.

• Sanitation-Removeanddestroyinfectedplantsandplantremains

• Disinfectseedmaterials


Cucumber

• Timelyapplicationsofeffectivefungicidescanbebeneficialforcontrol

• Deepplowingofplantdebrismaybehelpful

Black Root Rot

Causal agents – Pythium. sp, Thiela viopsis basicola. Low temperature and high moisturecontentofthesoilarerequiredforinfectionanddiseasedevelopment.Highsoilmoisture (soil saturatedwithwater) is probably themajor environmental factoraffecting disease development. The pathogens overwinter in the soil and in infested plant debris in and on top of the soil, in certain organic fertilizers, peat, and in or on seeds and transplanting material.

The disease is most severe when cucumber is produced on the same field for several yearsinsuccession.Highplantingdensitythatresultsinpooraircirculationandslowerdrying time of plant tissues also contributes to disease development, especially ofseedlings.Thepathogenspenetratetheplantthroughtherootsystem,throughwoundsorothertypesofdamageexistingonrootsandroothairs.

DiseaseSymptoms:Thediseaseaffectsbothnewlyemergedseedlingsandmatureplants. In the case of newly emerged seedlings, the disease can cause massivedestructionof thecrop,especiallyonwet (saturated) soils. Leavesondiseasedplantlose turgor and wilt, but retaintheir green color and do not fall down. Base of the stembecomes thickened.Thevascular tissue (waterconduction tissuesof theplant)becomes discolored. After making cuts through the lower part of the stem and upper partoftheroot,achangeincoloroftheinnertissuesisclearlyvisible.Infectedtissuesdevelopadark raspberry (purplish)colored.Thedisease isworse inwetareasof thefield,especiallywherefloodinghasoccurred.

Control

• Use crop rotation.

• Use culturalpractices that avoid excessive succulence andplantgrowth ,overtime.

• Sanitation-Removeanddestroyinfectedplantsandplantdebris.

• Goodagriculturalpracticesandsanitary-hygienicmeasures,includingcleaningagriculturalequipmentbeforeenteringnewfieldsarerecommended.

• Avoid planting in fields or areas with poor soil drainage (soils saturated with water).

• Timelyapplicationsofeffectivefungicidescanbeimportantforcontrollingthedisease.

Anthracnose

Causal agent – Colletotrichum lagenarium. Anthracnose is a serious disease of cucumber that can result in significant yield losses under favorable conditions fordisease development. The disease affects the leaves, stems, stalks and fruit. The fungus overwinters in infested plant debris in and on top of the soil. The fungus can also be carriedonseedharvestedfrominfectedfruit.Freewateronplantsurfacesarerequiredfor infection and disease development. Free water from rain fall and overhead irrigation

Figure 4.4 Symptoms of anthracnose on cucumber. Source: GrowLust - Growing An Edible Garden

Figure 4.3 Symptoms of black root rot. Author: Jason Brock

Figure 4.5 Symptoms of gummy stem blight. Author: Don Ferrinine

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Chapter 4

andhighhumidityarenecessaryforthegerminationoffungalspores,andtheirspread.Sporesarespreadmainlybysplashingwater,butcanalsobespreadbyinsects,wind,peopleandmachinery.

The optimal temperature for spore germination and growth is 22° to 27°C, withrelative humidity of 100 percent for 24 hours. Visible symptoms of the disease canappearat96hoursafterinfection.

Disease Symptoms:All parts of leaves, stems and fruits can be infected. The first symptomsappearasroughlycircularlightbrowntoreddishspotsonleaves,stemsorfruits.Leavesbecomeinfectedatearlystagesofplantdevelopment.Leavesdevelopthedistinct spots, the number and size of which depends on climatic conditions that are favorablefordiseasedevelopment.Spotsgraduallyincreaseinsizeandnumber,causingleavestodryandbecomedistorted.Thecentersofthespotsmayfalloutcausingashotholeeffect.Onstemsandfruitstalks(petioles),spotsareshallow,elongated,andtanin color.When stemsbecomediseased, it is importantwhere the infectionoccurs. Ifinfectionsoccurnearthebaseofthestem,theymaygirdlethestemandtheentireplantcandryupanddie. If infectionsoccuronhigherpartsof theplant,newshootsmaydevelop on the lower part of the plant.

Onfruit,spotsarecircular,sunken,andwater-soaked.Spotsonfruitusuallydevelopas the fruitbegins to ripen (mature)nearharvest. Fruit infectionoftenoccurfirstonthe skin of the fruit that is in contact with the ground. The number and size of spots increaseswithtime,theymergeandoccupylargeareasoffruitsurfaceandmayalsocoveritcompletely.Ifdiseasedfruitssurvive,theyoftenhaveabittertaste.

Control

• Usecroprotationwithaminimumofthreeyearswithoutreplantingcucumberorothersusceptiblecropsinthecucurbitaceaefamilysuchasmelons.

• Select andusevarieties andhybrids,whichare comparatively resistant to thedisease.

• Sanitation-Removeanddestroyinfectedplantdebrisfromthefieldorgreenhouse.

• Timely applications of effective fungicides are important for controlling thisdisease.

GummyStemBlight

Causal agent – Didymella bryoniae. Gummy stem blight is a serious disease ofcucumberinthefieldandgreenhouse.Thediseasecancauseextensivedamageonallabove ground parts of field and greenhouse grown cucumbers. The disease on fruits in the field and in storage is called black rot. The fungus overwinters in debris from old infected plants in or on the surface of the soil and can be carried on infected seed. Fluctuatingtemperatures,excessiveirrigationorrainfall,incorrectplacementofplants(excess of plants per unit area) that reduces air circulation, and damage caused bynematodes contribute to development of this disease.

Disease Symptoms: On leaves, symptoms visually resemble sunburn. Withcareful inspection, thickened areas on infected leaves can be observed. Large leaves developyelloworreddish–brownspotswithvariousshapes.Thespotsgrowinsize,losecolorandassumeaquasi-circularshape.Often,spotsoccupyoverhalfoftheleaf area.


Cucumber

Diseasedareasdevelop smallblackdotswhichare fungal fruiting structures thatproducesporesthatcanspreadthedisease.Stalkandsteminfectionsusuallydevelopatthebeginningofthestalkandwhereitbranches.Moistureusuallyaccumulateseasilyat this locationon the stem. Infectedareasdevelopwet spots,whichdry,developagrayishcolorandbecomecoveredwithblackdots(fungalfruitingstructures).Infectedfruitsoften,lookliketheyhavebeenboiled,blackenandthendryup.

Control

• Usecroprotationwithaminimumofthreeyearswithoutreplantingcucumberorothersusceptiblecropsinthecucurbitaceaefamily.

• Disinfectseedmaterial.Alwaysstarttheplantingwithhighqualitydiseasefreeseed and transplanting material.

• Observinganoptimal irrigationregime.Avoidoverwateringplantsandwaterthematthetimeofdaywhentheplantswilldrythefastest.Inthegreenhouse,anywateringmethodthatpreventsabovegroundplantpartsfromgettingwetwillgreatlyaidindiseasecontrol.

• Sanitation-Removeanddestroyinfectedplantsandplantdebrisfromthefieldand greenhouse.


Cladosporium(Scab)

Causal agent – Cladosporium cucumerinum. Cladosporiumis a widespread disease of cucumberworldwide. Itmostly affects fruit, butunder conditionsofhigh relativehumidityitmayalsoinfectstems,leaves,andseedlings.Thegreatesteconomiclossesfromscabcomefromfruitinfections.Thediseaseismostsevereduringrainyandcoolsummer periods, with rapid changes in temperature. Under hot summer conditions diseaseseverityisreduced.Diseaseseverityincreaseslateinthegrowingseasonduringthefinalperiodofcucumbervegetation,whenrelativelycoolnightswithdewappear.

Ingreenhouses,thisdiseaseismostsevereunderconditionsofrapidtemperaturechanges and high relative humidity. Increased temperature significantly reducesdiseasedevelopment.Thecausalagentspreadsbymeansofsplashingwaterfromrainoroverheadirrigationandwind.Itoverwintersinandontopofthesoilininfectedplantdebris.

Disease Symptoms: Fruit infections cause the most economic damage. Fruit infectionsbeginassmall(2-4mm),greasylookingsunkenspecksonthefruitsurface.These specks enlarge, become circular to oval in shape, gray in color, and remainsunken.Avelvetylayerofdarkgreenfungalgrowthmaydeveloponthesurfaceofthelesion.Lesionsoftenoozeastickyexudatethatdriestolooklikedropsofhardenedjelly.Spotsmaycoalescetoformlargesunkencratersandcavities.Thefruitskinoftencracksandsecondarydecayorganismscolonizeinfectedtissuesandcauseadditionalfruitrot.Infected fruitsoften becomecrooked.On leaves, water-soaked, pale green, irregularlyshapedspotsdevelop.Thespotsenlargeandturngraytobrownincolor.Eventuallytheinner tissue of the spot breaks and falls out, leaving irregular shaped holes and tears in theleaf.Infectedleavesmaybecomedeformed.Underhumidconditions,spotsontheleafandstemscanbecomecoveredwiththepowderydarkgreengrowthofthefungus.

Figure 4.6 Symptoms of cladosporium. Source: Forestry Images

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Chapter 4

Control

• Usecroprotationwithaminimumofthreeyearswithoutreplantingcucumber.


• Maintainanoptimalventilationregimeingreenhousestopromotefasterdryingof all plant parts.

• The temperature in greenhousesafter transplanting of seedlings must be no lowerthan17°to18°C.Immediatelyupondiscoveryofthefirstsymptomsofthedisease,itisnecessarytoregulaterelativeairhumidityat70to75percent.

• Whenwateringplantsinthegreenhousetrytoavoidgettingplants(leavesandfruits)wet.Irrigateplantsinthefieldatatimeofdayorunderconditionsthatwillallowtheplantstodryquickly.


DownyMildew

Causal agent – Pseudoperonospora cubensis. Downymildew is a very commonand serious disease. Under environmental conditions that favor disease development (cool,wetweatherandhighrelativehumidity)downymildewcandestroytheentirecropifitisnotcontrolled.Itaffectsmostcropsinthecucurbitaceaefamily.Thediseaseaffects cucumber in the field and in greenhouses. The pathogen is an obligate parasite soitcanonlyinfectlivingplants.Theoomycetepathogenrequiresfreewaterinordertoinfectandproducesporetospreadthedisease.Whenweatherisdryorifcucumberisplanted inadry locationor region,downymildewshouldnotbeaproblem.Thefungusoverwintersas thickwalled restingspores (oospores) in the soilor infectedplant debris on top of or in the soil. The thick walled oospores can survive for long periods of time.

DiseaseSymptoms: InGeorgia, thediseaseusuallystarts todevelopwhenyoungplantshavethreetofiveleaves.Thefirstsymptomsarepalegreenareasontheupperleafsurface.Theseareassoonbecomeyellowincolorandangulartoirregularinshapeandareborderedbytheleafveins.Asthediseaseprogresses,theleafspotsmayremainyelloworbecomebrownandnecrotic.Duringmoist,wetweather,theareaundertheleafspotonthebottomsideoftheleafbecomescoveredwithawhitishtopalegrayfuzzygrowthof thepathogen(thedownymildew).Severelyaffected leavesmaydryupanddieresultingindefoliationoftheplants.Diseasedevelopmentisfavoredbydayandnighttemperaturesof18°to22°Candthepresenceofwaterdropsordewontheplant’s surface for a period of at leasteight to nine hours. Under such conditions, the pathogenformsmaximalnumbersofsporesandthediseasecanspreadveryquickly.Onceinfectionhasoccurred,thepathogencanproducesporesoninfectedtissuesinaboutfourdays.Thesesporesstartanotherinfectioncycle.Relativelyseldomdoesthedisease affect cucumber fruits and steam. When it does, dark spots appear on the fruits, while on the steam the disease rots the stalk and dries the plant from the diseased area towards the top.

Figure 4.7 Symptoms of downey mildew on cucumber. Source: State University Cooperative Extension


Cucumber

Control

• Observeoptimalhumidityandaerationregimesinthegreenhouse.

• Sanitation- Remove anddestroy diseasedplants and old infectedplant debrisfrom the field or greenhouse.

• Selectandusecucumbervarietiesandhybridsthatareresistanttothepathogen.

• Underconditionsfavorablefordiseasedevelopment,thetimelyapplicationofeffectivefungicidesisveryimportantforcontrollingthisdiseaseonsusceptiblevarieties.

Alternaria Leaf Spot

Causal agent – Alternaria cucumerina. Alternaria leaf spot can infect several crops in thecucurbitaceaefamily.Thepathogencansurvive(overwinter)asfungalmyceliumininfestedplantdebrisontopoforinthesoilforonetotwoyears.Thesourceofinoculumthatfirst introduces the disease are spores (conidia) that are produced by dormantmyceliuminfieldswherethediseasewaspresent.Theconidiacanbecarriedforlongdistancesbywind.

High temperatures and the presence of free water from rain, irrigation or dew on leafsurfacesarerequiredforinfectionanddiseasedevelopment.Thediseasecanbeaseriousproblemingreenhouseswithpoorventilationandhighrelativehumidity.Rapidchanges in temperature and failure to remove infected leaves and other plant parts from the planting also contribute to disease development and spread.

DiseaseSymptoms:Thefirstsymptomofthediseaseistheformationofsmallyellowbrownspotswithalightgreenoryellowhalo.Spotsfirstappearonolderleavesnearthetopoftheplantthenspreadtootherpartsoftheplant.Spotsquicklygrowinsizeandtheirdiameteroftenexceeds1cm.Spotsarefrequentlyalittlesunken.Whenthediseaseissevere,spotsmergeandcreatenecroticconcentricringsorzones.Severelyinfectedleavesmaybecomecup-shaped,dryupanddie.

Control

• Usecroprotationwithaminimumofthreeyearswithoutreplantingcucumber.




Target Spot

Causal agent – Corynespora Cassiicola. The fungus can survive (over winter) ininfestedplantdebrisinorontopofthesoilforatleasttwoyears.Thefungusproducesspores(conidia)thatarespreadbywind.Rapidchangesoftemperature,wetconditionsfromrain,irrigation,dewandhighrelativehumidity,combinedwithhightemperaturesare climatic conditions favorable for infection and disease development

Figure 4.8 Symptoms of alternaria leaf spot. Author: Howard F. Schwarts

Figure 4.9 Symptoms of cucumber target spot. Source: Forestry Images

Figure 4.10 Symptoms of Fusarium stem and root rot. Source: Applied and Environmental Microbilogy

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DiseaseSymptoms:Thefirstsymptomsappearonolderleaves,asspotsofvariousshapes that are grayish-yellowish in color, dry and slightly protruding on the leaf’ssurface. Under wet, humid conditions, a dark powder develops on the bottom side of the spots. In greenhouses, spot centers are of comparatively lighter color than inthefield. Incasesofseveredisease, infected leavesbecomenecrotic,dryupanddieresulting in defoliation of the plant.

Control



• Observingsanitary-hygienicrulesingreenhousesandtheiradjacentterritories.


Fusarium Stem and Root Rot

Causal agent–Fusariumoxysporum.The pathogen is soil borne and can survive in the soil for 15-16 years or longer.The fungus penetrates the plant through roothairs, and through wounds caused by mechanical damage,insect pests and otherformsofrootinjury.Thediseaseismostseverewhencucumberandothercropsinthecucurbitaceaefamilyaregrowninmonoculturewithoutadequatecroprotationtohelpreduce pathogen populations in the soil.Environmental conditions that favor disease developmentarehightemperaturescombinedwithlowrelativehumidity.

DiseaseSymptoms:Plantsmaybecomediseasedatanystageoftheirdevelopment.Seedlingsgerminating fromseedscanbecome infectedanddiebefore theyemergefromthesoil.Afteremergence,seedlingsthatareinfectedareoftenstuntedandmaydie.Onolderplants,symptomsofwiltingaremoreobviousduringbloomandfruitset.Initially,theupperpartoftheplantbeginstoturnyellowandwiltduringthehottestpart of the day.Wilted plants may appear to recover at night as temperatures cooldown and plant transpiration decreases. Leaves on infected plants often have dead areasthatcanlooklikesymptomsofnutrientdeficiency.Whenstemsofwiltedplantsarecutlengthwiseatthesoilline,theyoftenhaveabrowndiscolorationinthewoodytissueimmediatelyunderthebark.VineskilledbyFusariumcanbecomecoveredwithapinkish–whitefungalgrowthinwetweather.Fruitsfromdiseasedplantsareextremelybitter.

Control

• Because the funguscan survive in soil forup to16years, crop rotation isnotconsidered to be effective for controlling this disease. If cucumber must bereplantedininfestedfields,croprotationsofthreetofouryearsmaybehelpfullowering the amount of Fusarium in the soil.Disinfect soil in the greenhousethrough heat treatment or fumigation. Soil fumigation in the field can be effective,butisveryexpensive.

• SelectanduseofcucumbervarietiesandhybridsthatareresistanttoFusariumwilt whenever possible.


Cucumber

• Avoid introducing the fungus into new fields and greenhouses. The fungus can bespreadoninfectedplantingmaterial,equipment,tools,feetandsurfacewaterthat is contaminated with infested soil.

GrayMold

Causal agent–Botrytis cinerea.Thisdisease ismost severeonnon-self-pollinatedvarieties.Thefunguspenetratestheplantmostlythroughwoundsorolddyingflowerparts. The fungus can survive in soil or plant debris in or on top of the soil as sclerotia. Sclerotiaarelongtermsurvivalstructuresofthefungus.Itcanalsosurviveasmyceliumininfestedplantdebris.Fungalconidiadevelopinspringonsclerotiaorfrommyceliumin plant debris and are the source of inoculum for new infections. Low soil temperature, irrigatingwithcoldwater, improperplantingdensity that reducesair circulationandincreasesdryingtimeofplantpartsandbadventilation ingreenhousesareallfactorsthat favor disease development. Under the proper conditions, the disease can cause serious losses in the field and in greenhouses.

Disease Symptoms: Thedisease canaffect leaves, stems and stalks (petioles) ofcucumber.Symptomsfirstappearassmallwet(water-soaked)spots.Intimeandunderwetormoistconditions,thesurfaceofdiseasedtissuesbecomescoveredwithagraypowderygrowthofthefungus.Thisiswherethediseasegetsitsname(graymold).Thegraypowderyfungusgrowthconsistsofmyceliumandconidiaofthefunguswhichcanserveasinoculumtospreadthedisease.Infectedfruitcanbecomecompletelycoveredwiththegraymold.Fruitmayrotandcollapse.

Control



• Observesanitary-hygienicrulesingreenhousesandtheiradjacentterritories.


CucumberDiseasesCausedbyVirusesCucumberMosaicVirus(CMV)

Causal agent – Cucumber mosaic virus. Cucumber mosaic is a serious disease of cucumber.Thevirusisspreadorvectoredbyinsects,primarilyaphidsandespeciallythepeachaphid.Thevirusbecomesdeactivatedeasilyundernaturalconditionsandcannotoverwinterinplantremains.Itoverwintersinaphidreservationareas,weedsandintheaphids themselves.

DiseaseSymptoms:Diseasesymptomsofmostdiseasescausedbyvirusesarehighlyvariabledependinguponmanyfactors.Often,thefirstsymptomsofthediseaseappearonyoungleaves.Atthistime,leavesdeveloplightgrayoryellowishspots.Withtime,thenumber of spots increase and they frequently cover the entire leaf.Greenwart-likestructuresoftendevelopat thesametime.Leaveseventuallybecomedeformed,developchlorosis,necroticspotsanddryupanddie.Diseasedplantsareusuallystunted

Figure 4.11 Symptoms of cucumber grey mold. Source: American Phytophatology Society

Figure 4.12 Symptoms of cucumber mosaic virus. Author: William M. Brown

Figure 4.14 Bacterial Soft rot and wilt of cucumber. Source: Snipview

Figure 4.13 Symptoms of cucumber green mottle mosaic virus.Source:Snipview

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with the distance between plantnodes (internodes)shortened.Infected fruit are lightgreenatfirst,thenturnyellow.Fruitareusuallydeformed,withwart-likestructuresontheir surface and are greatly reduced in size. If plants become diseased during thesecondhalfofthegrowingseason,reducedgrowth(stunting)maynotbeobservedatthistime,butfruitmaystillbedeformed.

Control


• Selectanduseofcucumbervarietiesandhybridsthatareresistanttocucumbermosaic whenever possible.

• Controlinsectsthatspread(vector)thedisease,especiallythepeachaphid.

CucumberGreenMottleMosaic

Causal agent – Cucumber green mottle mosaic virus. This disease is most common in greenhouses. It often causes stunting of plant growth. Cucumber green mottlemosaicviruscanremainactiveindiseasedplantremains,existinginthesoil.Incertaincases,virusmayalsospreadthroughinfectedseedmaterial.Thediseasehasnotbeenreportedtobetransmittedbyinsects.

DiseaseSymptoms:Greenwart-likestructuresdeveloponyoung leavesand fruit.Leavesareoftendeformed. Insomecases,necroticareasdeveloponleavesandmayturn white.

Control

• Use crop rotation.Cucumber crops should be rotated with tomato or pepper, since these crops are not considered host plants of this particular virus.

• Useonlyvirusfreeseedsandplantingmaterial.

• It is necessary to avoid rapid changes in temperature in the greenhouse. Itshould also be notedthat chances of spreading of this disease diminish when soil temperatureexceeds16°C.

• Sanitation-Removeanddestroyvirusinfectedplantsandplantdebrisfromthefieldand greenhouse.


CucumberDiseasesCausedbyBacteriaBacterial Soft Rot and Wilt

Causal agent – Pseudomonas burgeri: Bacterial soft rot and wilt is a serious disease ofcucumber inGeorgia. If thediseasebecomessevere,crop lossesof40percentorhigher canoccur.Thediseasemay appear at any stageof plant development.Thebacteria survive and over winter in infected seed andinfected plant remains on top of or in the soil.

DiseaseSymptoms:Initialsymptomsarewet(water-soaked),darkgreenspotsthatdevelop along the central vein of the leaf.The spots darken with time. Spots later merge anddevelop into largenecroticareasof2-3cm.If theplantsbecome infectedat the

Figure 4.15 Symptoms of bacterial wilt of eggplant. Source: Missouri Botanical Garden


Cucumber

twotosixleafstage, they loseturgorpressureandcanwilt in thehottestpartof theday.Whentemperaturesbecomecooleratnight,wiltedplantsmayrecoverandappearnormal.Thisphenomenonmaycontinueforseveraldays.Finally,thewiltingbecomesirreversibleandtheplantbecomesseverelywilted.Infectedstalksbecomeverysoftandwhencutlengthwise,darkenedvesselsandtissueinsidethestalkareeasilynoticeable.Sometimesthisdiseasedoesnotproduceatypicalrot.Insuchcases,theplant’sgrowthisstunted,lowerleavesdry,andthefruit,ifitdevelops,isnotmarketable.Wet(water-soaked)spotswith adiameterof 0.1-0.2 cmdevelopon fruits thathave soft rot.Thecentral part of these spots later darkens, as a result of death of the cellson the fruits surface.Inlaterstagesofsoftrot,fruitcontentsbecomebrownandrotted.Thebacteriaspreadthroughtheplantbymeansofvessels.

Control



• Prevent movement of bacteria from plant to plant and from location to location onhands,toolsandotherequipment.

• Ensure optimal plant nutrition regime. Do not over fertilize, especially withnitrogen.

• Disinfestseedandalwaysstarttheplantingwithhighquality,disease-freeseeds.

• Disinfestsoilwithheattreatment(inthegreenhouse)orsoilfumigation.

BacterialWilt(Bacteriosis)

Causal agents – Erwinia tracheiphila: Causal bacteria can overwinter on and in infected seeds.The incubationperiod(the time from infectionuntil visible symptomsdevelop)forthediseaseisfivetotendays.Whenthediseaseissevere,croplossesof40percentandmorecanoccur.Optimalenvironmentalconditionsfordiseasedevelopmentaretemperaturesof26°to28°Candrelativehumidityof95-100percent.

DiseaseSymptoms:Infectedplantswiltandusuallydiewithintwoweeks.Infectedstemsdevelopyellowishstripesontheirsurface.Thesestripeslaterdarkenandburst.Wheninfectedstemsarecut,reddish-browntracheae(vasculartissue)canbeobservedinsidethestem.Onleaves,small,wet(water-soaked),chlorotic(yellowish)spotsarethefirstsymptomstodevelop.Thesespotslaterincreaseinsizeandtheirdiameterreachesapproximately0.8-1cm.Intime,spotschangetheircolorandbecomedarkredordarkbrown. Fruitsfrom diseased plantshave chlorosis (yellowing), become hardened andmaydevelopwet (water-soaked)oroily lightbrownspotsontheirsurface,whichare0.3-0.5cmindiameter.Infectedfruitsarenotmarketable.

Control • Sanitation-Removeanddestroyinfectedplantsandplantdebrisfromthefield

and greenhouse.• Observesanitary-hygienicrulesingreenhousesandtheiradjacentterritories.• Prevent movement of bacteria from plant to plant and from location to location

onhands,toolsandotherequipment.• Ensure optimal plant nutrition regime. Do not over fertilize, especially with

nitrogen.

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• Disinfestseedandalwaysstarttheplantingwithhighquality,disease-freeseeds.Disinfestsoilwithheattreatment(inthegreenhouse)orsoilfumigation.

PhysiologialDisordersVeryfewabioticdisorderareassociatedwithcucumberfruits.Onlytwomajorabiotic

disordersareknowntoaffectfruitquality.Thesearefruitbitternessandchillinginjury.

Fruit bitterness

The bitterness in cucumber is linked to a group of chemicals called cucurbitacin. These chemicals are found in higher concentration in the leaves and stems, but at a verylowconcentrationinthefruit,exceptinwildcucumberswheretheyarepresentataveryhighconcentration.Thesechemicalsaretoxictohumanwhenconsumedinlargequantities.Severalexplanationshavebeensuggestedastowhysomecucumberfruitsbecome bitter. Some varieties have been reported to be prone to produce fruits with higher concentration of cucurbitacin than others and in some cases plants within a certainvarietymayproducemoreof thechemicals thanothers.Non-genetic factorsthat can increase cucurbitacin include vines grown under certain stresses (such as sever moisturefluctuation),andlowtemperaturesoftenproducebitterfruits.Also,misshapenfruitsaremorelikelytobebitterthanwell-shapedfruits. Improperfertilizerratesandspacing were also suggested to increase bitterness in cucumber.

Control

• Plant varieties that produce low bitter fruits.• Transplantcucumbersintothefieldafterthelastdayoffrost.• Ensurethatplantsreceivemaximumsunlight,especiallylateintheafternoon.• Avoidfluctuationinsoilmoisture.• Avoidplantingveryclosetooneanother.• Ensurethattheplantsreceiveadequateandbalancedfertilizers.

Chillinginjury

Cucumbers and other warm season crops like tomatoes, peppers, eggplants, and melonsarechillingsensitiveattemperaturesbelow10°Cifheldformorethanonetothree days, depending on temperature and cultivar. Symptoms of chilling injury arewater-soakedspots,pittinganddecay.Chillinginjuryiscumulativeandmaystartinthefieldbeforeharvest.Also,cucumbervarietiesaredifferent insusceptibility tochillinginjury.

Control

• Harvestthecropearlyinthemorningwhenfruitsareattheircoolesttemperature.Iftheambienttemperatureislowerthan12oC,thendelayharvestuntilthefruittemperaturerisestoabout15°to18oC.

• Storefruitsbetween10°to13°C.Anaveragestoragelifeofcucumberfruitsstoredat13oCisbetween10and14days.

• Ifacooler isnotavailable, thenkeepfruitsmoistandcoverwithawetburlapcloth to serves as an evaporativecooler.

Figure 4.16 Symptoms of chillinginjury in cucumber. Source: North Carolina Cooperative

Figure 4.17 Symptoms of cucumber, when it is stored with ethylene producing fruits like tomato and pepper. Source: North Carolina Cooperative


Cabbage belongs to the genus Brassica, species oleraceae,varietyBrassicaceae and cultivargroupcapitata.Membersofthisfamilyincludecabbage,cauliflower,broccoli,Brusselssprout,kale,radish,mustard,andmanyothers.

Cabbage varieties

Cabbagetypesexistinseveralshapes,sizesandcolors.Themostcommontypesaregreen, savoy, red, Napa, bokchoy, and Brussels sprouts.Mostformtightheads,exceptbokchoy. Ingeneral,headcabbagerequiresbetween60to100days fromsowingtoreachmarketmaturity,dependingonthevariety.

Climaticrequirements

Cabbageisacool-seasoncrop,whichcangenerallytoleratelightfreeze(0°to-1°C).CabbagecanbegrownasaspringcroporafallcropinmanymoderateclimateareasofGeorgia.Plantscantolerateahardfrost(-2°Cforafewhours),howeverexposureto-2°Corlowerformanyhourscancauseseveredamageordeathoftheplants.

Idealmonthlytemperaturesforoptimalgrowthanddevelopmentrangefrom16°Cto18°C.However, cabbageandotherbrassicacropsmaybecomesubject tobolting(prematureappearanceofaflowerorseedstalk)whenexposedtocertaintemperatures.Floweringusually occurs after an extendedperiodof exposure to low temperatures(below10°C)followedbyaperiodofwarmertemperatures.Usually,exposuretoabove24°Cafterexposuretolowtemperaturemaycauserapidbolting,butvarietiesdifferintheirsusceptibilitytothisdisorder.Boltingistheprocess inwhichtheplantswitchesfromvegetativegrowth (heading) to reproductivegrowth (formationof flowers andseeds). This switch becomes evident when seed stalks appear, making the headsunmarketable.Thepresenceofaseedstalkisnotalwaysvisiblefromtheexteriorofthehead.Theheadmayhavetobesplittoobservetheseedstalkformingfromthebaseofthe plant. Varieties differ in their tolerance to temperatures that induce bolting. Losses toboltingincabbageoccuralmostannually,particularlyinoverwinteredcropsthatareexposedtoseveretemperatures.

Nutritionalrequirement

Soil pH influences plant growth, availability of nutrients and activities ofmicroorganisms in the soil. Keeping soil pH in the proper range is important for productionof thebestyieldsofhighqualitycabbage.TheoptimumpHforcabbageproduction isbetween6.0 to6.5.Calcium (Ca)has limitedmobility in soil, therefore,limeshouldbebroadcastandthoroughly incorporatedtoadepthof15to20cmtoneutralizethesoilacidityintherootzone.Toallowadequatetimeforneutralizationofsoilacidity(raisingthepH), limeshouldbeappliedandthoroughlyincorporatedtwoto three months before seeding or transplanting. However, if application cannot be madethisearly, limingwillstillbebeneficial ifappliedandincorporatedat leastonemonthpriortoseedingortransplanting.Generally,maintainingasoilpHof6.0to6.5willprovideadequatesoilCalevels.WhensoilCafallsbelow400to450kgperhectare,calciumdeficiencyproblemsmaydevelop.

Because calcium levels can vary considerably in a field, soil calcium should bemaintainedat550kgperhectareor slightlyhigher. If the soilpH is in theoptimum

Cabbage

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rangeof6.0and6.5andthesoilCalevelisbelow560kg,thenapply900to1100kgofcalciumsulfate(gypsum)perhectare.Thegeneralfertilityrecommendationforcabbageistoapplyenoughfertilizertoprovideabout150kgeachofnitrogen(N),phosphorus(P2O5),andpotassium(K2O)perhectare.Thiscanbedonebyapplying900kgof10-10-10perhectarebybroadcastorbandplacementmethodsbeforeplanting.Alsoapply4.0to8kgofBoraxpertonoffertilizer.Ifboronisnotappliedwithpre-plantfertilizer,spray12KgofSoluborperhectaredirectlytothebaseofyoungplants.Cabbagehasahigherdemandforboronthanmanyothervegetablecrops.Aborondeficiencycaninduceaphysiologicaladisordercalled“hollowheart.”Hollowheartcausesthepithofthehead(center)tocrackandturnbrownastheheadreachesmaturity.

Sidedresswith15to30kgofnitrogenperhectareattwoweeksaftertransplantingor about fiveweeks after direct-seeding. Side dress againwith the same rate threeweeks later.

Planting methods

Although cabbage canbedirect seeded,mostproducers use transplants.Direct-seedingofcabbagerequiresusingaprecisionseedertoplaceasingleseedatdesireddistances from one another. For optimum seed germination and stand establishment, soil temperatures must be above 5°C, otherwise seeds will be lost to damping-offand rotting, causing poor or uneven stand. Some growers choose to produce their owntransplantsinnurserieswithtransplantsbeingdugfivetosevenweekslater.Itisestimatedthat20gramsofcabbageseedsproduceabout3,500transplants.

Foraspringcrop,settransplantsinthefieldinlateFebruaryorearlyMarch.Forafallcrop,field-seedingshouldstartduringthefirsthalfofAugustorduringthelasthalfofJulyinnorthernareas.Ifusingtransplantsinthefall,plantaboutonemonthlaterthaniffield-seeding.Preparethelandearlybyturningthesoilsothatanycropresidueisfullydecomposedbeforetransplantingordirect-seedingisdone.Spacetransplantsat30to40cmapartintherowand90to100cmbetweenrows.Thisspacingwillproduceheadsofabout1.0to1.5kg.

Irrigation

Cabbage is a fast-growingplantwith shallow rootspenetratingonly 30 to 40cmintothesoil.Althoughcabbage is relativelydroughttolerant,adequatesoilmoistureshouldbemaintainedinordertomaximizeyields.Themostcriticaltimeforirrigationisfollowingdirectseedingortransplantingandduringheaddevelopment.Anywaterstress during these periods can lead to small head size, cracking of the head, or tip burn.

Use of plastic mulch

Plastic(Polyethylene)mulchoffersseveraladvantagesingrowingmanyhorticulturalcrops. Plastic mulch increases soil temperature, which can accelerate plant growth and development, it conserves soil moisture, reduces soil compaction, leaching of fertilizer, soil moisture evaporation, and competition from weeds. Most growers use double rows spaced25to30cmapartbetweenrowswithintherow,and80to90cmbetweenrows.Usingplasticmulchaddstotheproductioncosts;however,thecostcanbeoffsetbyearlierandlargeryieldofhigh-qualityheads.Inordertospreadtheincreasedcostover

Figure 5.1 Symptoms of clubroot in cabbage. Source: The Biking Gardener: New Plants


Cabbage

twoseasons,growerscanplantanothercrop(doublecropping)beforeoraftercabbageharvest. Care must be taken throughout the growing season not to tear or damage the mulch. Double-cropping with tomatoes, peppers, ormelons will spread productioncost over two crops.

Controlling Weeds

Plantingrelatedcropsyearafteryear inthesamefieldwill increasepestpressurein that field causing an unlikely chance to produce a marketable crop of cabbage.The use of cover crops can also be used in a rotation. Crop rotation is one of the most effective pest management strategies that a grower can use to reduce pest pressure. Avoidproducingcabbage inareaswhereanyrelatedcropsweregrownthepreviousseason. The longer the rotation, the more effective the pest control will be (three to four years is ideal).An ideal four-year crop rotation for cabbage includesoneof thefollowingfamilies:thecucurbitaceaefamilycucumbers,watermelons),followedbytheSolanaceae family (tomatoes, bell peppers, eggplant), and the leguminaceae family(beansandpeas).

CABBAGEDISEASESCabbage has several diseases that can be very serious under environmental

conditionsthatareconducivetodiseasedevelopment.Diseasesofcabbagearecausedby fungi,virusesandbacteria.Mostcabbagediseasesarecausedby fungi.Themaindiseasesthatarecausedbyfungi include:Clubroot,DownyMildew(perenosporosis),AlternariaLeaf Spot (alternariosis), Black Leg, FusariumWilt, Gray Mold, White Rust,Rhizoctonia (rhizoctoniosis) and SclerotiniaWhite Rot. The most important diseasecausedbyavirusiscauliflowermosaic.

Important diseases causedbybacteria includebacterial soft rot andblack rot ofcabbage.

CabbageDiseaseCausedbyFungi Clubroot of Cabbage

Causal Agent – Plasmodiospora brassicae. Clubroot is a world-wide problem intemperate climates on several important crops in the family brasicaceae including,cabbage,broccoli,cauliflower,radishesandturnips.Itiscausedbyasoil-bornefungusthatonlyinfectsplantsinthefamilycrucifereae.Itinfectsthroughroothairs.Onceinsidetheplant, itstimulatesabnormalgrowthofinfectedtissuesresultinginswollenclub-shapedgalls.Infectionisfavoredbyexcesssoilmoisture(saturatedsoils),lowpH(5.6to6.5)andtemperaturesof18°to25°C.However,thediseasecanoccuroverawiderangeofconditions.Onceaplantisinfected,manysporesofthefungusareproducedinsideofinfectedtissueswithinthe“club-shaped”galls.Thesesporescansurviveinthesoilforatleast10yearswheretheycancausenewinfections.Thesporescanbemovedbywind,water,machinery,peopleandanythingelsethatcanmoveinfestedsoiltonearbyfieldswheretheycancausenewinfectionsandcontinuetospreadthedisease.

Diseases Symptoms: The roots of plants affected by this disease develop club-shapedgalls.Thefungusinduceshypertrophy(anincreaseincellsize)andhyperplasia(anincreaseincellnumber)muchlikecancerinmammals.Thedistortedtissueblocks

Figure 5.2 Symptoms of downey mildew on cabbage. Source: Vegetable Pathology – Long Island Horticultural Research & Extension Center

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theprocessofabsorptionofwaterandmineralsubstancesbytheroots.Wheninfectionis severeandoccursearly, this can result ina stuntingofplantgrowth, yellowingofthefoliageduetoreducedmineraluptake,andwiltingoftheplant,especially inhotweather.

Onplantsthatarenotseverelyinfected,thediseasemaygounnoticed.

Below ground galls are not visible and appearance of the plant above the earth’s surfacemaynotchangegreatlyasaresultofthedisease.Itisoftenpossibletodiscoverthisdiseaseonlyasaresultofinspectionoftherootsystemforthepresenceofgalls.

Diseasedseedlingsarecompletelyuselessforfurtherproduction,sincetheycannotformrootsanddevelopadequately.

Control

• Clubrootisaverydifficultdiseasetocontrol;

• SinceclubrootisfavoredbylowsoilpH,addinglimetothesoiltoincreasesoilpHto7.2orabovemaybehelpful.However,raisingpHtoohighmaybeharmfulto other crops;

• Observingtherootsystemwhiletransplantingseedlingsandremovingdiseasedplantsisimportant.Theuseofpathogen-freeseedbedsanduninfectedplantsisessential to prevent introduction of the disease;

• Croprotation–Growingcabbageonthesamesoilnomore thaneveryfive toseven years is important to prevent thedevelopment of largepopulations offungalsporesonlandthatisnotalreadyheavilyinfested.HeavilyinfestedareasmayhavetobeabandonedfromproductionofcabbageandotherplantsinthefamilyCruciferae;

• Controlweedsinandneartheplanting,especiallyplantsinthefamilyCruciferae;

• Cleananddisinfestallmachineryandotherequipmentbeforemoving it frominfestedtonon-infested“clean”fields;

• The use of fungicides in transplant water or applied to the soil at or before planting,maybehelpfulincontrollingthisdisease.

DownyMildew(Perenosporosis)

Causal Agent – Peronospora brassicae gaum. Downymildewaffectsall cultivatedplants in thecruciferae family. It canbeavery seriousdiseaseoncabbage,broccoli,cauliflower,radishandturnip.Underfavorableconditionsfordiseasedevelopment,itmaycauseseriouslossesinthefieldandcandevelopafterharvestinstorage,causingarotthatcanreducethequalityoftheproductinpackingandshipping.

Theoomycetepathogenoverwinters in rootsor indecayingportionsofdiseasedplants.Thepathogenproduces thick-walled resting spores calledoospores in stems,cotyledons,andotherfleshypartsofinfectedplants.Theoosporescansurviveforlongperiodsoftime.Ongrowingplants,thepathogenproduceslargenumbersofanothertypeofsporethatareblownbywindorsplashedbyraintocausenewinfectionsinthefield. Moisture and temperature are important in the spread and reproduction of the pathogen.Highrelativehumidityduringcoolorwarmconditionspromotesthegrowthandspreadofthepathogen.Diseasedevelopmentslowsdownorstopsunderhotanddryconditions.Freewateronthesurfaceoftheplantfromfog,rain,deworirrigationis


Cabbage

requiredforthepathogentogerminate,infecttheplantandproduceadditionalsporestospreadthedisease.Sporescanbeproducedonnewlyinfectedplantpartsinaslittleasfourdays.

DiseasesSymptoms:Plantscanbe infectedatanystageofdevelopment. In seedbeds, cotyledons and young leavesmay develop a fungal growth on the undersideofthediseasedleaf.Later,aslightyellowingdevelopsoppositethefungalgrowthontheuppersideoftheleaf.Onolderleavesinfectedareasgraduallyenlarge,turnbrightyellowthenbecometanandlikepaper.Undercool,moistconditions,awhitemildewgrowthcanbeseenontheundersideof infected leafspots.Severely infectedplantsmayrotanddieinthefield.

Thediseasealsospreadstocabbageheadsduringtheirwinterstorage.Grayishspotsdeveloponouterleaves,whichthendarkenandcausecabbagetorot.Thediseasemayalsoappearonsecond-yearplantingsandseedlandplots.

Control

• Crop rotation- Use a rotation that excludes the production of crops in thecruciferaefamilyforatleasttwooutofeverythreeyears;

• Sanitation-yessanitarymeasuressuchastheuseofcleanseedbedsawayfromtheproductionofcrops in thecruciferae family.Removeanddestroy infectedplant parts in the field and in storage;

• Controlweeds,especiallyplantsinthefamilycruciferae,inandneartheplanting;

• If severe disease is expected, applications of an effecting fungicide is veryimportant for controlling this disease. Weekly applications may be requiredstarting soon after plant emerge.

Alternaria Leaf Spot

Causal Agent – Alternaria brassicae. The fungus can infect most of the major crops in thefamilycruciferae.Thediseasedamagescabbageduringthefirstandsecondyearofproduction and in storage.

Whenthediseaseissevere,seedlossesmayconstituteupto60percent.Duringthefirstyear,damagecausedbythediseasetotheplantmaybeinsignificant,butdiseasedevelopmentduring thesecondyearcan result insignificant losses.Thediseasecanalsocausesignificantdamageandlossesinstorageandonyoungplantsafterplanting.Damageduringtheseperiodsismoreextensive,comparedtothefirstyear.

The pathogen can survive on infected plants and in infested crop residues. Free water is required for infection. A minimum of six to eight hours of leaf wetness isrequiredforinfection,andseverediseasecandevelopunderconditionsoflongperiodsofwarmandwetweather.Atleast12hoursof90percentrelativehumidityisrequiredfor the pathogen to produce spores on the surface of infected tissues. The optimum temperatureforsporeproductionis18°to24°C.Thesesporesarespreadbysplashingwaterfromrainor irrigationandbywind.Theyspreadthediseasebyinfectingotherplants.

DiseasesSymptoms:Onwhite-headedcabbage,duringthefirstyear,symptomsareobservedassmall,blackspotsmeasuring1to2mmindiameteron lower leavesandcabbage fruit walls. Later the spots enlarge into circular, tan to brown spots that are visibleonbothsidesof the leaf.Thesespotscanenlarge to5 to25mm indiameter

Figure 5.3 Symptoms of alternaria leaf spot. Source: Wikimedia Commons

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andusuallycontainconcentricrings,givingthespotsatarget-likeappearance.Spotssometimeshaveayellowmarginorhalo.Ifconditionsarefavorable,thefungusproducessporesandthespotsbecomecoveredwithavelvetygreengrowthofthefungus.Oldleafspotsdevelopatexturelikepaperandmaytear.Insecond-yearplants,thediseaseoften develops on cabbage fruit or rather bags of the walls, on the whole length. Such fruit is covered with black spots. Spots which develop at the ends, open the shoots at the ends, so their ends resemble scissors.

Control

• Alwaysusepathogenordisease-free seed. If seed is infected, apply fungicideseed treatments. Seed can also be treated using hot water soaks. Water is warmedtoatemperatureof50°Candseedsaresoakedatthistemperaturefor20minutes.Seedsarethenremovedfromthewaterandchilledincoldwaterandallowedtodry;

• Sanitation-removeanddestroydiseasedcrop residues fromtheplantingafterharvest;

• Timely applications of effective fungicides can provide good control of thisdisease.

BlackLeg(PhomaLeafSpotandCanker)

Causal Agent – Phoma lingam: Black leg is caused by the fungus Leptospharia maculans.The imperfector asexual stateof the fungus isPhomalingam.Theasexualstate of the fungus (Phoma lingam) produces tiny black dot-like fungal fruitingstructures (pycnidia)on thesurfaceof infectedtissues.Thesestructuresareuseful indiagnosing the disease. The fungus can affect all parts of the plant (leaves, stem, root, andbags).Thediseasemayoccurduringanyperiodofplantdevelopment.Thefungusoverwintersininfectedseedsandinfestedplantdebrisinandontopofthesoil.Itcanalsooverwinteronseveralweedsspeciesinthefamilycruciferaeandothercultivatedcropsinthecruciferae,especiallyrape.Freewateronthesurfaceoftheplantfromrain,dewor irrigation is required for the fungus to infect.Optimal conditions fordiseasedevelopmentincludetemperaturesof21°to25°C,relativehumidityof60to80percentandfreewaterontheplantsurfaceforaperiodof24hours.

Diseases Symptoms: On the leaves and stems of young plants, brown spots ofvarioussizesdevelop.Thegrowthofdiseasedplantsisstuntedandseverelydiseasedplantsmaydie.Spotsgraduallydarken,dry,andcontainmanydark,tinyfungalfruitingbodiescalledpycnidia.

Whenmatureplantsbecomediseased,yellowishtograyishsunkenspotsdevelopon the main stem at their root necks or foundations of side roots. These spots also developtheblacktinyfungalfruitingbodiesattheircenters.Therootneckandmainbranchesofthediseasedplantdevelopaninternaldryrot.Theybecomehollow,dryupanddisintegrate.Theseplantseventuallydieasaresultofthedisease.

Control

• Alwaysusepathogenordisease-free seed. If seed is infected, apply fungicideseed treatments. Seed can also be treated using hot water soaks. Water is warmedtoatemperatureof50°Candseedsaresoakedatthistemperaturefor20minutes.Seedsarethenremovedfromthewaterandchilledincoldwaterandallowedtodry;

Figure 5.4 Symptoms of cabbage black leg. Source: OSU Extension Plant Pathology


Cabbage

• Crop rotation-Use a rotation that excludes the production of crops in thecruciferaefamilyforatleasttwooutofeverythreeyears;

• Sanitation-Removeanddestroydiseasedcropresiduesfromtheplantingafterharvest;

• Avoidplantingcabbagenexttofieldsofoilseedrape;

• Timely applications of effective fungicides can provide good control of thisdisease.

Fusarium Wilt

CausalAgent–Fusariumoxysporum.Fusarium wilt is a serious disease of cabbage andcanresultinsignificantlosses,especiallyonearlyvarieties.Thefungusissoil-borneandproducesatypeofspore(chlamydospore)thatallowsitsurviveinsoilformanyyears.

Itmainlyaffectsseedlings,bothinthetraysandaftertheyaretransplantedintothefield.Underconditionsthatarefavorablefordiseasedevelopment,thedeathofyoungseedlingsmayreach20to25percent.

The fungus penetrates the plant through wounds that are usually created bymechanical damage. The fungus moves through the above ground part of the plant bycolonizingthevascularsystem.Growthofthefungusandtheproductionofsporesinside the plant plugs up the water and food conduction vessels of the plant. This severelylimitstheuptakeofwaterandnutrients.Thisresultsinayellowingandwiltingoftheplant,especiallyinhotweather.Theoptimalconditionfordiseasedevelopmentisasoiltemperatureof15°to17°C.Airtemperatureandrelativehumidityhavelittleeffecton disease development.

DiseasesSymptoms:Themainsymptomofthisdiseaseisyellowgreenishcoloringoftheleaves,oftenononesideoftheplant.Infectedplantslooseturgorpressureandwilt,especiallyinhotweatherorduringthehottestpartoftheday.Leavesdevelopunevenly.Theydevelopmorestronglywheregreencolorpredominates.

When stalks and leaf stems from diseased plants are cut in cross section with a knife, alightordarkbrowncircleofdiscoloredtissueisvisibleinthevasculartissue.Diseasedleavesfalldown,theheadisdistorted.Incaseofseveredamage,onlynakedheadremains.

Control

• Preventthemovementofinfestedsoilintoclean,uninfectedfieldsonmachinery,otherequipmentandanythingelsethatcanmovesoil;

• Maintainagoodfertilityprogramforcabbage.Therearesomereportsthatsaypotassiumdeficiencycanincreasediseaseseverity;

• Sanitation-removeanddestroyinfectedplantremains;

• Select and use resistant plant varieties if available.

GrayMold

Causal Agent – Botrytis cinerea. Gray mold is one of the most widespread andseriousdiseasesofcabbageandotherplantsof thecruciferae family.Oncabbage, itisespeciallysevereandcauses thegreatest lossesduringstorage.Mostoften,plants

Figure 5.5 Symptoms of fusarium wilt in cabbage. Source: Ontario crop IPM

Figure 5.6 Symptoms of gray mold in cabbage. Author: Geoff Dixon

Figure 5.7 Symptoms of white rust in cabbage. Source: Flicker

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becomeinfectedneartheendofsummer,duringrainyweather,orwhenthereisdueonthe cabbage for long periods of time.

Various types of mechanical damage also contribute to infection and diseasedevelopment.

The fungus survives and overwinters as conidia and sclerotia on plant remains in andontopofthesoilaswellasinplantsinstorage.Thediseaseisspreadbymeansoffungalspores(conidia)thatoftencomefromstorageareas.

Diseases Symptoms: During storage, under conditions of high temperature andrelativehumidity,thesurfaceofcabbageheadsbecomescoveredwithagraymassoffungalgrowth(mold),whichconsistsoffungalspores(conidia)andmycelium.Leavesrot and become mucous.

In diseased tissues, after a certain period of time, there can be observed blackfungal structures called sclerotia. These are survival structures of the fungus that can remainviableforlongperiodsoftime.Thediseasespreadseasilytohealthyplantsbywindblownorwater-splashedconidia.Thefungussometimesinfectsnewlyemergedplants resulting in death of the seedlings.

Control

• Useproperagriculturalproductiontechniquethatminimizedamagetotheplantandresultsinhealthyvigorousplants;

• Sanitation-Removeanddestroyinfectedplantremainsinthefieldandespeciallyin storage;

• Carefulandthoroughcleaninganddisinfestingofstorageareasisnecessary;

• Provide optimal storage conditions (temperature and relative humidity)throughout storage;

• Thetimelyapplicationsofeffectivefungicidesandpost-harvestdipsoffungicidescan be helpful in controlling the disease.

White Rust

Causal Agent – Albugo candida. Apart from cabbage, the causal agent also affects manyothercropplantsandweedsinthecruciferaefamily.Thediseasecanaffectleaves,blossom clusters and stems. The pathogen is soil borne and survives in plant remains in andontopofthesoilandinthesoilalone.Itproducesthick-walledoosporesthatallowittosurviveinthesoilforlongperiodsoftime.Oosporesgerminateinplantremainsor in the soil and produce swimming zoospores. Zoospores swim or are splashed onto theplantwheretheycauseinfectionsthatresultinraisedpustules.Freewateronthesurfaceoftheplantfromrain,deworirrigationisrequiredforinfection.Anothertypeofspore(sporangia)isproducedonthepustulesandthesesporangiaspreadthediseasewithinthecropprimarilyinsplashingwater.Infectionscanoccurwithinfourtosixhoursunderoptimalconditions.Theoptimumtemperatureforinfectionis20°C.

Diseases Symptoms: Early symptoms are small, raised, white- or cream-coloredblistersthatmeasure2to3mmindiameterthatformundertheepidermisonleaves,stems andflowers talks.The epidermis covering theblisters soon ruptures releasingpowderywhitefungalstructures(sporangia).Intime,largerblistersrangingfrom2to3cmindiametermaydevelop.

Figure 5.8 Symtoms of rhizoctonia in cabbage.Source: Departments of Agriculture and Food Australia


Cabbage

Distortionofleavesiscommonandleavesmaydevelopayelloworreddiscoloration.Severelyinfectedleaveswitheranddie.Intime,olderpustulescanbecomerottenandbrown.Infectedblossomclustersbecomedistorted.Blossomclusterstemsthickenandtheir ends become twisted.

Control

• Crop rotation - Use a rotation that excludes the production of crops in thecruciferaefamilyforatleasttwooutofeverythreeyears;

• Sanitation-Removeanddestroydiseasedcropresiduesfromtheplantingafterharvest.Deepplowingtobury infectedplantremains isbeneficial inreducingthespreadofsporestonearbycrops;

• Select and use resistant varieties if available;

• Timelyapplicationsofeffectivefungicidescanprovidegoodcontrolofthisdisease.

Rhizoctonia

Causal Agent – Rhizoctonia solani. Rhizoctonia survives and overwinters in plant residuesinandontopofthesoilandinsoilaloneasmyceliumofsclerotia.Sclerotiaare specialized structures that allow the fungus to survive for long periods of time in thesoil.Myceliumandsclerotiacausethefirstinfectionsonseedlingsandolderplants.Thediseaseisfavoredbywarmsoiltemperatures(25°to30°C),butiscapableofcausingproblemsatmuchlowertemperatures.InGeorgiathediseasemostlyaffectslateheadcabbageinrainyfallconditions.

Thisdiseaseisespeciallydangerousforspecializedfarmsandmonocropproduction.

The disease can be very damaging in storage, especially under poor storageconditions with high temperatures. The higher the temperature in the storehouse, during storage periods, the quicker the disease spreads. The fungus spreads fromdiseasedtohealthycabbageheadsthroughdirectcontact.

Diseases Symptoms:Themain symptom characteristic of Rhizoctonia is cabbageleafrot.Diseasedleavesdevelopwet,lightbrowncolorspotswithanirregularshape.Intime,awhitishgrowthoffungusmyceliumcanbeobservedontheirsurface.Lateron,bothspotsandmyceliumdevelopadarkercolor.Adark-brownwebofmyceliaandsclerotiadevelopalongthecentralveinoftheleaf.Outerleavesgraduallyyellowanddryupandmaydie.

Control



• Do not plant in fields that have under composed residues from crops in thecruciferae;



• Fungicide treatments in the field have had limited effectiveness.

Figure 5.9 Symptoms of sclerotinia white rot in cabbage. Source: Departments of Agriculture and Food Australia

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Sclerotinia Rot (WhiteMold)

Causal Agent – Sclerotinia sclerotiorum. Thefunguscausesdiseaseonmanyspeciesofplants.Thediseaseismorecommononheavy,claysoils.Poorstorageconditions(hightemperaturesandrelativehumidity)andwarmwetconditionsinthefieldcontributetodiseasespreadandseverity.

Diseases Symptoms:When the disease appears in the field, root neck and lower leaves are damaged. Diseased tissue loses color, becomes wet (water-soaked) andvelvety white growth of fungal mycelium develops on the surface. In autumn, themyceliumthickensandtransformsintoblack,variously-shapedsclerotia,thediameterofwhichfluctuatesbetween1mmto3cm.

Whitemold isespecially seriousduringstorage.Damagestartsoncabbageheadouterleavesinthefieldbeforeharvest,especiallyduringrainyweather.

Underpoorstorageconditions(hightemperatureandrelativehumidity),cabbageheadleavesbegintorot,becomeslimyandfungalmyceliumdevelopsontheirsurface.Intime,sclerotiadevelopamongthemycelia.Thefungusspreadseasilyfromdiseasedtohealthycabbageheads,asaresultofdirectcontact.

Control

• Careful and thorough cleaning and disinfesting of storage areas;



• Sanitation-Removeanddestroyinfectedplantremainsinthefieldandespeciallyin storage.

CabbageDiseasesCausedbyVirusesCauliflowerMosaic

CausalAgent–Cauliflowermosaicvirus.Cauliflowermosaicvirusinfectswhite-headedcabbage, leaf cabbage,kohlrabiandcauliflower.Thecausalvirus spreadsbymeansofplantjuice,aswellascabbageandpeachaphidsandmembersofsuperfamilyAphidoidea. Sources of the virus are other infected crop plants and susceptible weed in the cruciferae family.Optimaltemperatureforspreadofcauliflowermosaicvirusis160to180С.

Diseases Symptoms: Disease symptoms appear four to five weeks aftertransplanting. Veins of diseased plants become chlorotic and assume a lighter color, then develop dark green spots. Leaves become deformed because veins stop growing. Sometimessmallnecroticspotscanbeobservedondiseasedleaves.Incaseofseveredamage, necrotic spots may develop and leaves may drop prematurely. Underconditionsofhightemperatures,diseasesymptomsmaydisappear.Astemperaturesbecomelower,thesymptomsmayreappear.

Control

• Alwaysstarttheplantingwithpathogen(disease)freeseedsortransplants;

• Removeanddestroyinfectedplantsfromthefieldandcontrolweedspeciesin

Figure 5.10 Symptoms of cauliflower mosaci virus. Source: Departments of Agriculture and Food Australia

Figure 5.11 Symptoms of bacterial soft rot. Source: Plant Disease and Insect Clinic


Cabbage

thecruciferaefamilyinandneartheplantingthatcanserveasasourceofthevirus;

• Control aphids and other insect pests which can transmit the virus.

CabbageDiseaseCausedbyBacteria Bacterial Soft Rot

Causal Agent – Erwvinia carotovora, Erwvinia aroideae, and Pseudomonas Spp. Conditionsfavorableforspreadingofsoftrotincludewarmweather(200to250C)andrelative air humidity within 50 percent. The bacteria generally penetrate the plantthroughwoundscausedbymechanicaldamage,variousinsectpests(cabbageflyandcabbagebugs),andotherplantdiseases.Sourcesofinfectionaremostlyinfectedplantremainsontopoforinthesoilandcontaminatedequipmentorstoragefacilities.

DiseasesSymptoms: First symptomsof thediseasemaybeobservedat theearlyleafstage.Atthistime, leavesdevelopoilyspots,asaresultofwhich infectedplantsstop growing and may die. Disease development and spread becomes massive(extensive or widespread) during the second vegetation stage. At this point, outerleavesofdiseasedcabbageheadsdarken,becomeslimyandrot.Thediseaseismostsevereunderconditionsofwarmtemperaturesandhighrelativehumidityorwetness.Thediseasegraduallyspreadstothewholecabbagehead,whichrotscompletelyandbecomes separated from the stem. This process is accompanied with an unpleasant smell.Itshouldbenotedthatiftopleavesofthecabbagearedamagedbydiseaseandthisperiodcoincideswithdryweather,thedamagedareasmaybecomedry,thinandtransparent.Insuchcases,itispossibletolocalizespreadofthisdiseaseonthecabbagehead.Diseasedevelopmentsometimesbeginsfromthecrownofthecabbage,inwhichcase it softens, development stops, and the heads fall off.

The disease can also cause serious losses in storage. Cabbage, which is diseased but nosymptomsarevisibleduringitsinspection,beginstorotinstorageiftemperaturesexceeds30to40Candrelativehumidityishigh.Thebacteriamoveeasilyfromdiseasedtohealthycabbage,whichspreadsthedisease.

Control

• Use proper agricultural production technique that minimizes damage to theplantandresultsinhealthyvigorousplants.Maintainingproperplantnutritionto prevent nutrient deficiencies is important;



• Provide optimal storage conditions (temperature and relative humidity)throughout storage. Storage temperature should be close to 00C and never exceed40C;

• Observe crop rotation: theoptimaloption isgrowingcabbageafterbeet andlegumes;

• Preventdamagetoheadsthroughtimelyandhigh-qualitychemicaltreatmentagainstpests(cabbageflycontrolisespeciallyimportant)andotherdiseases.

Figure 5.12 Symptom of black rot on cabbage. Source:Cornell University College of Agriculture and Life Sciences

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Black Rot of Cabbage

CausalAgent–Xanthomonascampestris.Black rot isavery importantdiseaseofmanycropsinthecruciferaefamily.Thecausalbacteriacansurviveandoverwinterininfected seed, diseased weeds and in infested crop remains that are not decomposed. The main source of infection is infected seed material Bacteria which penetrate the seedscan invadetheseedrootandthenspread into theplant.Water is required forinfectionandthediseaseisspreadwithinthefieldmainlybysplashingwater.Duringquickchangesbetweendayandnighttemperatures,dewappearsonleafedges,whichallowsthebacteriatoeasilypenetratetheplantthroughnaturalopenings.Thediseasereducesthemarketqualityandvalueofcabbage.

DiseasesSymptoms:Thefirstsymptomsofthediseaseappearthreetofourweeksafter planting of cabbage seedlings. At the first stage of cabbage rosette development, the edges of lower leaves develop localized black spots, on which blackened vessel nets areeasilyvisible. It ispossibletoseeblackenedvesselsonstemscut incrosssectionwith a knife with the unaided eye. Leaf veins blacken, while tissue between themyellows. Damaged tissues dry and thin. Disease symptomsmay also bemanifestedasyellowingof leafedges.When thestem isdiseased, thevascular systembecomesdamaged.Thestembecomespluggedwithbacterialooze,which isproducedbythebacteriareproducinginsideit.Vesselsblacken,dryandfailtoperformtheirnecessaryfunctions.Diseasedplantsoftencannotformheads,whileiftheheadsstillappear,theyareunderdevelopedandofpoorquality.

Control

• Always use pathogen or disease-free seed or plantingmaterial. Seed can betreatedusinghotwater soaks.Water iswarmedtoa temperatureof50°Candseedsaresoakedat this temperature for20minutes.Seedsare thenremovedfromthewaterandchilledincoldwaterandallowedtodry;

• Crop rotation- Use a rotation that excludes the production of crops in thecruciferaefamilyforatleasttwooutofeverythreeyears;

• Use proper agricultural production techniques that minimize damage to theplantandresultsinhealthyvigorousplants;

• Sanitation-removeanddestroydiseasedcropresiduesfromtheplantingafterharvest;

• Systematicreplacementofinfestedsoilingreenhouses,orsteamtreatmentandfumigation of infected soils;

• Timelyandhigh-qualitychemicaltreatmentagainstharmfulinsectpestswhichtransfer the disease.

PhysiologicalDisordersLeaf tip burn

Tipburnisthedeathofthemarginsofexpandingyoungleaveswithinthecabbagehead.Theoutsideleavesareusuallynotaffectedbytipburn.Howeverwhenanaffectedheadiscutopentipburnwillbevisibleasdarkareasatthemarginsofyoungleaves.Tipburn is often associated with periods of rapid growth. The resulting tissues are often weak andsusceptibletodeterioration.Thedefectispossiblycausedbyashortageofcalcium


Cabbage

associatedwithrapidgrowthandwaterstress.Varietiesdiffer insusceptibility tothisdisorder,andusinganon-susceptiblevarietyisthebestpracticestoavoidtheproblem.Additionally,avoidoverfertilizingtheplants,especiallyatyoungage.AdjustingsoilpHto6to6.5andkeepingadequatesoilmoisturewillalsoreducetipburn.

Head splitting

Maturecabbageheadsmaysplitifnotharvestedinatimelymanner.Splittingoccurswhen the stem and internal leaves grow after the head is mature, putting too much stressontheouterleavesformingthehead.Itoccursmorefrequentlyafterarainstormor over irrigation. Earlymaturing varieties tend to splitmore easily, they should beharvested soon after the head reaches the marketable stage to avoid the problem.

Hollow Heart

Cabbageandotherbrassicacropshaveahigherdemandforboronthanmanyothervegetables.Aborondeficiencyresultsinthedevelopmentofaconditioncalled“hollowheart.”Withhollowheart,thepithofthehead(center)becomescrackedandbrownasthecabbagereachesmaturity.Toavoidhollowheartdevelopment,apply5to10kgofBoraxpertonoffertilizer.Ifboronisnotappliedwithpre-plantfertilizer,spray10kgofSoluborperhectareor2litersofN-Boronperhectaredirectlytothebaseofyoungplants.

Post harvest handling

Winterproducedheadcabbagecanbestoredforuptooneyearunderidealstoragetemperatureof-10to10Candrelativeof96to98percent.However,ifnocoldstorageisavailable,cabbage,unlikebroccoliorcauliflower,cantoleratestorageoutdoorsandincellarsprovidedthatthetemperaturedoesnotdropbelow120C.Ifstoredoutdoorsduring the fall and winter, cabbage heads should be kept moist and in shaded areas.

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Tomato (LycopersiconesculentumMill.)isoneofthemostwidelygrownvegetablesintheworld,plantedinmorethan160countries.AccordingtotheUnitedNationsFoodandAgriculturalOrganization(FAO),worldproductionoftomatoin2014wasestimatedat about 120million tonswith an increase ofmore than 35 percent in the last tenyears.About75percentoftheproductionissoldforfreshmarketandtheremaining25percent isprocessed into juice,paste,andsundried.Tomato fruitsare rich in thecarotinoidlycopene,whichisrelatedtovitaminAandbetacarotene.Carotenoidsareverypowerfulantioxidantsandhavebeenreportedtohaveanti-cancerproperties.

EnvironmentalRequirements

Tomato is a warm season crop requiring air temperature in the range of 20oto 32oC. However, for optimum plant growth, soil temperature is more important than air temperature.Tomatoesshouldbeplantedwhendaytimesoil temperature isnot lessthan16°C.When tomatoesare seeded tooearly in cold soils, seedlingswillnotgrowuniformlyand/ortheymaynotgrowatall.Additionally,rootdevelopmentofseedlingsgrownincoldsoilswillbeveryslowandtheywillhavedifficultyabsorbingnutrients,especiallyphosphorous.Blackplasticmulchisoftenusedtowarmupthesoil.

SoilRequirements

Tomatoplantswillgrowonmosttypesofsoils,however, theextenttowhichtherootsystemwilldevelopisaffectedbythesoilprofile.Rootgrowthwillberestrictedifthereisahardpan,acompactedlayer,oraheavyclayzone.Tomatoesareconsideredto be deep rooted and under favorable conditions, some roots will grow to a depth of asmuchasthreemeters.Themajorityofroots,however,willbeintheupper25to50cm of soil.

Since root development is severely limited by soil compaction, proper landpreparation should significantly reduce or eliminate soil compaction problems. Useof leguminous andnon-leguminous crops like alfalfa,wheat, oat, or rye cover cropshelpincreaseorganicmatterinthesoilandimprovesoilaeration.OptimumsoilpHforgrowingtomatoisabout6.8.

NutrientsRequirement

Tomato plants demand moderate amounts of fertilizer. The greatest demand occurs in thefirst8to14weeksofgrowth,andpeakabsorptiontakesplaceafterthefirstharvest.Therefore,plantsrequirehighnitrogen,phosphorous,andpotassiumapplicationsearlyinthegrowingseasonwithsupplementalapplications,especiallynitrogen,neededafterthefruitinitiationstage.Itisestimatedthatplantsremovefromthesoil3to4kgeachofnitrogenandpotassium,2kgofcalcium,0.5kgofphosphorous,and0.5kgofmagnesiumforeverytonoftomatofruitsproduced.Thegeneralrecommendationratesforthemajornutrientsinclude52kgnitrogen,120kgpotassium,and100kgphosphorousperhectare.Nutrienttreatmentsarebestwhenbasedonbothsoilandleafanalysis.Leafanalysisisabetterpredictorofthenutritionalstatusoftheplantthansoilanalysis.Forpotassiumandphosphoroustheyareappliedatonetime,usuallyafewdaysbeforetransplanting,whilecalciumapplicationisusuallymadethepreviousfallbeforetransplanting.Insomeinstances,plantsgrownincoldsoilscouldshowphosphorusdeficiency,whichresultsinplants being stunted with purple leaves on the underside.

tomato


tomato

Varieties

Tomatoes are classified into several groups based on the growth habit of the plants, fruitshape,fruitcolor,andprocessingqualities.

Tomato varieties are classified into two groups based on their growth habits, determinate and indeterminate.

• Determinate tomatoes shootgrowth terminateswith a flowerbud. Plants areusuallymore compact, reaching about twometers in height.Varieties in thisgroupusuallyproducefewerfruitsthatmatureearlyandinashortperiodoftime.Determinatevarietiesareusuallyfieldgownandtheydonotrequiresupport.

• Indeterminatetomatovarietiesformflowerbudsalongthesidesoftheshootsallowing the plants to continue to grow reaching many meters in height,especiallywhengrownundercontrolledenvironment.Thesevarietiesaregrownfor fresh market and they are more suitable for greenhouse or high tunnelproduction, because they continue to produce fruits for several months aslong as the growing conditions are favorable. However, indeterminate varieties requirewiresortwinesforsupportinordertokeeptheplantsfromlodging.Whengrown outdoor, indeterminate varieties will continue to grow until the weather condition is no longer favorable. Both greenhouse and outdoor indeterminate varieties require continuous care by removing suckers and positioning theshootstoallowforairmovementandlightexposure.

Tomato varieties are also classified based on the shape of their fruits.

• Beeforsteaktomatoesareroundandvaryinsizefrom50gramsuptoseveralhundredgrams.ThebiggeststeaktomatogrownintheUSweighedalmost3.5kg.Steaktomatoesaregrownprimarily for freshmarketand juiceproduction.However,theyarenotgoodforprocessingintopasteorsundryingbecauseoftheir low soluble solids.

• Roma tomatoes are oblong in shape and have high soluble solids content, which makethemmoresuitableforprocessingintopasteandsundryingandforlongdistance shipping, because of their high firmness.

• Cherrytomatoesarethesmallestsizetomato.Theyaregrownprimarilyforfreshmarket.

Tomatovarietiesarealsoclassifiedbasedontheir fruitcolor into red,yellow,andpurple.Mostcommerciallygrownvarietiesarehybrids.Afewopenpollinatedheirloomvarieties are still on the market.

CulturalRequirements

Irrigationisessentialtoproduceconsistentyieldsofhighqualitytomatoes.Rainfallamountsareoftenerraticduringthegrowingseason,especiallywhenplantsaregrowninsandysoilswithlowwaterholdingcapacity.Dripirrigation,plasticmulch,andraisedbedsarethepreferredmethodsofgrowingtomato.Sprinklerirrigationisusedinmanycountries but the risk of fruit cracking makes sprinkler irrigation less desirable.

Weedcontrolisveryessentialforoptimumtomatoproduction.Weedcontrolmeasuresinclude hand weeding, hoeing and chemical control. Check with the local GeorgiaExtensionOfficeforthelatestinformationonchemicalweedcontrolinyourarea.

Figure 6.1 Symptoms of anthracnose on tomato. Author: Bruce Watt

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Chapter 6

Harvesting and Postharvest Handling

Tomatofruitsareveryperishable,theyareusuallyharvestedbasedontheirdistanceto themarket.Tomato fruits picked for longdistancemarkets are usually harvest atthe mature green stage, a stage when the fruit skin is dull green and the seeds are surroundedbya soft jelly-likematerial called theplacenta.Fruits canalsobepickedatthebreakerstage,whenthefruitskinstartstoturnred,orwhenfullyripe,whenthedistancetothemarketisveryshort.Tomatofruitsareverysensitivetobruising.Toavoidbruising,fruitsshouldbeharvestedunderutmostcare,especiallywhentheyareatthegreenstage,inordertoreducetheriskoffailuretoripen.Theyshouldalsobepackagedproperlyinordertoavoidcompactionandcompressionbruises.

Tomato fruits are also sensitive to low temperature storage. Ripe fruits should be storedat14oto16oC,whilematuregreenfruitsshouldnotbestoredatlessthan18oC. Insomecountriesmaturegreentomato fruitsare treatedwithanethylenereleasingcompound called ethephon or ethrel in order to induce ripening.

TOMATODISEASESThere are several major diseases that can attack tomatoes on an annual basis. All

ofthemhavethecapabilityofcausingseriousdamagetothecroporevendestroyingit under the proper environmental condition. The plant pathogens that cause tomato diseases are fungi, bacteria and viruses.

Most tomato diseases are caused by fungi.These diseases include: Anthracnose,Early Blight (Alternariosis), Leaf Mold (Cladosporiosis), White Mold (Sclerotiniosis),VerticiliumWil,;LateBlight(Phytophthora),FusariumWilt,SeptoriaLeafSpot,PowderyMildew,BlackLeg(RootRot)andRhizopusRipeRot(WetRot).

Severalimportantdiseasesarecausedbybacteria.Theseinclude:BacterialCanker,Bacterial Wilt and Bacterial Spot.

Viruses can also cause some very serious diseases of tomato. Some of themostimportant inGeorgia include:TomatoMosaicVirus (TMV), ImpatienceNecrotic SpotVirus, and Stolbur Virus.

Some are caused from non parasitic organisms, such as Blossom End Rot of Tomato, yellowShoulderandothers.

TomatoDiseasesCausedbyFungi Anthracnose

Causal Agent – Colletotrichum coccoides. The fungus survives from crop to crop in infected plant debris in the soil. Wet and warm conditions are most conducive for diseasedevelopment.Conditionsthatfavorplantinfectionaretemperaturesfrom10oto 30oC(withanoptimumof20oto24oC).Freewaterontheplantsurfaceisnecessaryforsporegerminationand infection.The spores that cause infectionsare spreadmainlyby splashingwater from rainoroverhead irrigation.The fungus can infect seedlingsresulting inseedlingblight (death).Thefunguscanalso infecttherootsoftheplant.Fruit infection can be serious and result in severe disease losses. Fruit infections develop mostrapidlyonripeningandoverripefruit.


tomato

DiseasesSymptoms:Infectedrootsoffully-grownplantsbecomecoveredwithdarkspots.Thebarkstiffensandblackmicrosclerotia (small fungalstructures)accumulateunder the bark giving the roots a black appearance.

Onfruit,water-soakedcircularandoncavespotsfirstappearundertheskinasfruitripens.Withtime,thespotsdevelopadarkyellowcolor,inlaterstagesofdevelopment,spotsbecomedarkerandbecomeblackincolor.Thefungusproducesspores(conidia)on diseased tissues. These conidia result in further spread of the disease. The disease can developveryrapidlyduringstorageandtransportationtomarket,andduringartificialripening.

Control

• Sanitation-Removeolddeadplantsanddebrisfromthefield.Removeinfectedand over ripe fruit from the field;

• Crop rotation is an important cultural practice for control of soil borne diseases. Cucumber, onion, legumes, alfalfa, cabbage, and autumn wheat are considered to be good crops for rotating with tomato. Tomatoes should not be rotated with other solanaceous crops such as potato or peppers. For crop rotation to be successful,tomatoshouldnotbereplantedinthefieldsforatleastthreeyears;

• Prevent mechanical damage to the fruit and other plant parts;

• Harvest fruit at the proper time before it is fully ripened. Avoid letting fruitbecome over ripe in the field or in storage;

• Maintainproperstorageconditions.Fruitshouldbestoredat5oto6oC;

• Ifoverheadirrigationisrequired,applyitearlyinthedaysothatplantsdrybeforesundown;

• Planttomatoesinwelldrainedfieldstoavoidexcesssoilmoistureasfruitripen;

• Selectanduseaneffectivefungicidefordiseasecontrol.Agoodfungicidesprayprogramisveryimportantforcontrollingthisdisease.

EarlyBlight(Alternariosis)

CausalAgent–Alternariasolani,EarlyBlight(Alternariosis).Thisisaverycommondiseaseoftomato.Itcausesleafspots,fruitrotandstemlesionsontomato.Thediseasecanoccuroverawiderangeofclimaticconditionsandcanbeverydestructiveif leftuncontrolled,oftenresultingincompletedefoliationofplants.Incontrasttothename,itrarelydevelopsearly,butusuallyappearsonmaturefoliage.

Disease Symptoms:On leaves the first symptoms usually appear on older leavesand consist of small, irregular, dark brown to black, dead spots ranging in size from a pinpointto5to7mmindiameter.Asthespotsenlarge,concentricringsmayformasaresultof irregulargrowthpatternsbytheorganismintheleaftissue.Thisgivesthelesionacharacteristic“target-spot”or“bull’seye”appearance.Thereisoftenanarrow,yellowhaloaroundeachspotand lesionsareusuallyborderedbyveins.Whenspotsarenumerous,theymaygrowtogether,causinginfectedleavestoturnyellowanddie.Usuallytheoldestleavesbecomeinfectedfirstandtheydryupanddropfromtheplantas the disease progresses up the main stem.

On tomato, stem infections canoccur at any age resulting in small, dark, slightlysunken areas that enlarge to form circular or elongated spots with lighter-colored

Figure 6.2 Symptoms of early blight on leaf. Source: Cornell University

Figure 6.3 Symptoms of leaf mold. Source: Cornell University

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centers. Concentric markings, similar to those on leaves, often develop on stem lesions. Ifinfestedseedareusedtostarttomatotransplants,seedlingsmaydampoffsoonafteremergence. When large lesions develop at the ground line on stems of transplants or seedlings,theplantsmaybecomegirdled.

Control


• Sanitation:burnorburyalldiseasedplanttissueafterharvest;

• Use disease resistance when possible. Select varieties that have a lower susceptibilitytoearlyblight;

• Usecertifieddisease-freetomatoseedandtransplants;

• Use appropriate measures to control weeds and volunteer tomatoes in production areas;

• Maintain fertility at optimal levels - nitrogen and phosphorus deficiency canincreasesusceptibilitytoearlyblight;

• Timeapplicationsofoverheadirrigationtoallowplantstodrybeforenightfall;

• Althoughtheabovemeasuresareimportanttominimizeinfection,itisusuallynecessarytoapplyagoodfungicidesprayprograminordertoachievesatisfactorycontrol of the disease.

LeafMold(Cladosporiosis)

Causal Agent – Cladosporium fulvum. Leafmold (Cladosporiosis) is a commonand destructive disease on tomatoesworldwide. Leafmold is primarily a problemon tomatoes grown in greenhouses and high tunnels. It can also be a problem infields and garden-grown tomatoes under conditions that are favorable for diseasedevelopment.

Whenhumidityishigh,thefungusdevelopsrapidlyonleaves,usuallystartinginthelowerleavesandthenmovingupward.Ifthediseaseisnotcontrolled,largeportionsofthefoliagecanbekilled,resultinginsignificantyieldreductions.Earlyinfectionsarethemost damaging.

DiseasesSymptoms:Symptomsusuallydeveloponlyontheleaves.Thefirstsymptomis theappearanceofsmallyellowishcoloredspotsontheupper leafsurface.Onthelowerleafsurface,thefungusbeginstoproducevastnumbersofspores(conidia)withinthe infected tissue of the leaf spot on the bottom of the leaf. The fungus appears as an olivegreentograyishpurplevelvetygrowthconsistingmainlyoffungalspores.Thesesporesareeasilyspreadfromplanttoplantbyaircurrents,splashingwater,ontools,andclothingofworkers, andpossiblyby insects. Sporesgerminate inwaterfilmsorwhenhumiditylevelsareabove85percent,attemperaturesbetween4°and34°C.Theoptimumtemperature forgermination isbetween24°and26°C. Leavesare infectedthroughstomatawhenhumiditylevelsare85percentorhigher.Infectionoccursmostrapidlywhenhumiditylevelsattheleafsurfacefluctuatebetween85percent(day)and

Figure 6.4 Symptoms of blight on tomato. Source: Gardening Know How


tomato

100percent(night).Sporeproductionismostabundantatrelativehumiditybetween78and92percent,butcanoccurathumidityaslowas58percent.

Infectedleaftissuebecomesyellowishbrown,andtheleafcurls,withers,anddropsprematurely.Thewitheringanddefoliationprogressuptheplantuntiltheentireplantmayappeardryanddead.

Control

• Whenever possible, keep the relative humidity in the greenhouse below 85percent, and keep free moisture from forming or persisting on leaves. This will inhibit the development and spread of the leaf mold fungus;

• Provide good ventilation and as much light as possible. Circulate air with fans to eliminatedead-airpockets;

• Keep night temperatures in the greenhouse warmer than outside air temperatures;

• Attempttoavoidwettingtheleaveswhenwatering.Waterplantsearlyinthedaytoallowleavestodrybymid-afternoon;

• Maintainatemperatureofatleast16°to18°Cthroughouttheseason;

• Provideadequateplantandrowspacingtoavoidexcessiveshading;

• Leafmoldresistantvarietiesareavailable,butbecausethefungusmutatesreadily(thereareatleast12racesofthepathogen)resistantvarietiesareoflimiteduse.Becausenewvirulentracescandevelopinonlafewyearsatomatovarietywhichisresistantoneyearmaybeverysusceptiblethenext.Ifavailablegrowvarietieswith more than one leaf mold resistance gene;

• Reduce primary inoculums levels through sanitation, steam treatment ofgreenhouses, and seed treatment;

• Afterharvest,carefullyremoveanddestroy(burn)allplantdebris;

• Where possible, steam entire greenhouse sections between crops, preferablyonabright,hotdaywhenlittlesteamwillbeneeded.Closeallventilators,andmaintainthetemperatureat135°F(57°C)foratleastsixhours;

• Wherenecessary,usehotwatertreatedseed.Treatseedfor25minutesatexactly122°F(50°C);

• Afungicidesprayprogrammayhelpcontrolthedisease,butshouldbeconsideredsecondarytoenvironmental(cultural)controlmeasures. Iffungicidesareused,besuretothoroughly coverallabove-groundpartsofeveryplant,especiallythelowersurfaceofthefoliage,witheachspray.

SclerotiniaandSclerotiumBlight(Sclerotiniosis)

Causal Agent – Sclerotini ali bertiana and Sclerotium bataticola. Scelerotinia causes white rot and Sclerotium causes southern blight of tomato in the United States and throughout the world.

Both fungi penetrate the plant primarily throughwounds (mechanical damage).Bothdiseasesdevelopmost rapidlyunder conditionsof rapiddrops in temperature,high relativehumidity, dense vegetation canopy (which is characteristicofGeorgia),

Figure 6.5 Symptoms of verticilium wilt on tomato leaves. Source: Tatoo Pictures

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and conditions of poor ventilation in greenhouses. Both fungi survive in the soil and plant debris for very long periods of time, as sclerotia. Sclerotia are fungal survivalstructures that resist adverse environmental conditions in soil. These sclerotia serve as theprimaryinoculumforthedisease.Ingeneral,thedevelopmentofbothdiseasesisfavoredbysoilsthatarepoorintermsoforganicmatterandhavelowmicrobiologicalactivity.Theprogress of diseasedevelopment occursmore rapidly under conditionsof rapid changes or fluctuations in humidity and in temperatures lower than 20°C.Diseasedevelopmentdecreases,temperaturesrise,anddiseasedevelopmentceasesattemperaturesabove25°C.

DiseaseSymptoms:Major symptoms includeagradualwiltingof theplantandastem rotwith formationof cavities in thepith.These cavities arefilledwithwhitish-grayish fungal mycelia and large black sclerotia. Infected fruit have very distinctivesymptoms.Awhitefluffy layerofpowderyfungalgrowthdevelopsonthesurfaceofinfected fruit. In time, black sclerotia form on the surface of infected fruit. Infectedplantsusuallydieeventually.

Control


• Sanitation:burnorburyalldiseasedplanttissueafterharvest;

• Use disease resistance when possible, select varieties that have resistance;

• Maintainfertilityatoptimallevelsandmaintainsoilmoisturecontentat80to85percent;

• Selectanduseaneffectivefungicidefordiseasecontrol,Agoodfungicidesprayprogrammaybehelpfulforcontrollingthisdisease.

Verticilium Wilt

Causal Agent – Verticillium dahliae. Verticillium wilt is caused by the fungiVerticillium dahliae. The fungus attacks a wide range of plant species, including cultivatedcropsandweeds.Itissoil-borneinfieldandgreenhousesoilswhereitcanpersistformanyyears.

Disease Symptoms:Verticilliumwilt symptoms on tomato are similar to those ofFusariumwilt.Oftennosymptomsareseenuntiltheplantisbearingheavilyoradryperiodoccurs.Thefungusspreadsthroughtheplantwithinthevascularsystemwhereit can block water transport resulting in a wilt. The bottom leaves become pale, then tipsandedgesdieandleavefinallydieanddropoff.V-shapedlesionsat leaftipsaretypical ofVerticilliumwilt of tomato. Infected plants usually survive the season butaresomewhatstuntedandbothyieldsandfruitsmaybesmalldependingonseverityofattack.AlighttandiscolorationinthestemsimilartothatcausedbyFusariumwiltmaybefoundbutisusuallyconfinedtolowerplantparts.Thediscolorationistypicallylighter incolor thanwithFusariumwilt.Symptomsononesideof theplantonlyaresometimes seen. When infected stems are cut length wise, brown streaks in the vascular tissue can be observed well up into the plant.

Figure 6.6 Symptoms of late blight on tomato. Author: Bob Mulrooney


tomato

Verticilliumdahliaeismostactivebetween75oand83oF. Although disease is retarded bythehighertemperaturesthatfavorFusariumwilt,visiblesymptomsmayappeartobemore severewhenhigh temperaturesexist,due to restrictedwatermovement intheplantbroughtaboutbydamagedonetothewaterconductingvesselsearlierinthegrowing season.

Control

• BecausetheVerticilliumfungusiswidespreadandpersistsforseveralyearsinsoil,alongcroprotation(fourtosixyears)isnecessarytoreducepopulationsofthesefungi.Avoidusinganysolanaceouscrop (potato,pepper,andeggplant) in the rotation,and if Verticillium wilt is a problem also avoid the use of strawberries and raspberries, whicharehighlysusceptible.Rotatewithcerealsandgrasseswhereverpossible;

• KeeprotationalcropsweedfreebecausetherearemanyweedsthatareinfectedbyVerticillium;

• Ifpractical,removeanddestroyinfectedplantmaterialafterharvest;

• Maintain a high level of plant vigor with appropriate fertilization and irrigation, butdonotover-irrigate,whenpossible,especiallyearlyintheseason;

• When possible, plant disease resistant tomato varieties. If soils are heavilyinfestedwiththeVerticilliumfungus,itmaynotbepossibletogrowVerticilliumsusceptible varieties.

Late Blight of Tomato

CausalAgent–Phytophthorainfestants.Late blight is one of the most devastating diseasesoftomatoworldwide. If leftunmanaged,thisdiseasecanresult incompletedestruction of the tomato crop. Late blight is caused by the fungus Phytophthora infestans. Unlike most pathogenic fungi, the late blight fungus cannot survive in soil or deadplantdebris.Foranepidemictobegininanyonearea,thefungusmustsurvive,be reintroduced on seed tomato transplants, or live spores must blow into the planting alongwithrainstorms.Idealenvironmentalconditionsthatfavordiseasedevelopmentincludewarmdays(21°to29°C)andarelativehumiditynear100percent,followedbycoolnights(7°to15°C)withheavydew,fog,oralight,drizzlyrainthatpersiststhroughthe morning. Heavy overcast skies during the morning prevent temperatures fromrisingrapidlyandthefoliageremainswet.Inmoistweather,viablespores(sporangia)may be carried 20miles ormore by strongwinds and rain. Under ideal conditions,lesionsmayappearonleaveswithinthreetofivedaysafterinfection,followedbythegrowthofawhitemold(mycelium)soonafter.Sporangiaformedonthemyceliumarespreadrapidlybyirrigation,rainandequipment.Theyareeasilydislodgedbywindandrain and can be blown into neighboring fields within five to ten miles or more, thus beginninganothercycleofdisease.

Disease Symptoms: Late blight appears on tomato leaves as pale green, water-soaked spots, often beginning at leaf tips or edges. The circular or irregular leaf lesions areoftensurroundedbyapaleyellowish-greenborderthatmergeswithhealthytissue.Lesionsenlargerapidlyandturndarkbrowntopurplish-black.Duringperiodsofhighhumidityandleafwetness,acottony,whitemoldgrowthisusuallyvisibleonlowerleafsurfacesattheedgesoflesions.Indryweather,infectedleaftissuesquicklydryupandthewhitemoldgrowthdisappears.Infectedareasonstemsappearbrowntoblackandentirevinesmaybekilledinashorttimewhenmoistweatherpersists.

Figure 6.7 Symptoms of fusarium wilt on tomato plant.Source: Demo garden plots

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Late blight can also develop on green tomato fruit, resulting in large, firm, brown, leathery-appearinglesions,oftenconcentratedonthesidesorupperfruitsurfaces. Ifconditions remain moist, abundant white mold growth will develop on the lesions and secondarysoft-rotbacteriamayfollow,resultinginaslimy,wetrotoftheentirefruit.

Control

• Useonlyobviouslyhealthytomatotransplantsfreeofdarklesionsonleavesorstems.Whentransplanting,discardanddestroyalltomatoseedlingswithlesionson the stem and leaves;

• Volunteer tomatoes can be a significant source of spores of the late blight fungus. Allvolunteersshouldbedestroyedasquicklyaspossible;

• Growers should look (scout) fordisease symptoms in thefieldorgreenhouse.Diseasedplantsshouldberemovedfromtheplantinganddestroyed;

• Plant tomatoes as far as possible from potato plantings;

• Plant inawell-drained,poroussoilandfollowathree-yearrotationawayfromtomatoandexcludesusceptiblecrops;

• A good fungicide spray program is essential for adequately controlling thisdisease once it appears in the planting. If conditions are highly favorable fordisease development, and the disease becomes well established and widespread in theplantingorgreenhouse, fungicideswillprobablynotprovideadequatecontrol.

Tomato Fusarium Wilt

Causal Agent – Fusarium oxysporum. f. spp. Lycopersici.The fungus that causes Fusariumwilt is soilborneandsurvives in thesoil forvery longperiodsof time.Thediseaseattacksplantsatallstagesofdevelopment.Thediseaseisverydestructiveandoccursinalltomato-growingareasworld-wide.Lightsoilsfavordiseasedevelopment.Fusariumwiltismostseriousduringhotweather,whenairandsoiltemperaturesare25°to32°Cwithanoptimumatabout27°C.Thefirstsymptomsgenerallyappearaboutthetimeofbloomorsoonafterthesetofthecrown-clusterfruit,butinfectionsmayoccuratanytimeduringthelifeoftheplant.

DiseaseSymptoms:ThefirstsymptomofFusariumwiltingardensandfieldsisusuallythegoldenyellowingofa single leafletor shoot,ora slightwiltinganddroopingofthe lower leaves on a single stem. As the fungus develops inside the stem, plants show progressive yellowing, wilting, and withering starting generally with the lowermostfoliage.yellowedandwiltedleafletsdropearly.Oftenthesymptomsappearfirstonlyononesideofthestem.Affectedplantsturnabrightyellow,wilt,dryup,andusuallydiebeforematurity,producingfew,ifany,fruit.

Whentheepidermisandcorticaltissues(bark)onasectionofthemainstemclosetothebaseoftheplantiscutandpeeledback,adistinctchocolate-browndiscolorationofthewater-andfood-conducting(vascular)tissueisevident.Thestreaksextendfromthe roots up through the branches and into the petioles.

In dampweather, the pinkish-whitemasses of Fusarium sporesmay be seen ondeadvinesorinwoundsandleafscarsofseverelyinfectedplants.Seedbedinfectionscommonlycauseseverelosses.Affectedseedlingsarestunted.Theolderleavesdroopandcurveinward,theveinsarecleared,andtheleavescommonlydroop,laterwilt,and

Figure 6.8 Symptoms of septoria on tomato leaf.Source: Cornell University


tomato

die.Fruit infectionmayoccurandcanbedetectedbythebrowndiscolorationofthevascular tissue within the fruit.

SymptomsofFusariumwiltmaybeconfusedwiththoseofVerticilliumwilt,causedby a common soil fungus Verticillium albo-atrum (V. Dahliae). The two tomato wilts usuallycannotbedistinguishedexceptbyculturingthefungusinthelaboratory.

Control

• Plantonlycertifieddisease-freeseedandtransplants(ifavailable),well-drained,wilt-freesoil.TomatoseedtreatedproperlywithhotwaterisfreeoftheFusariumfungus;

• Disinfestgreenhouseand seedbed soilbeforeplanting,using steamorasoilfumigant (e.g., chloropicrin, Vorlex, methylbromide, etc.) fungi. Greenhousestructures, benches, containers, used stakes, and tools should be disinfested and pathogen free;

• Ininfestedsoil,growonlytomatovarietiesthatarehighlyresistantorimmuneto Fusarium and Verticillium wilts. For information on resistant varieties pleaseconsult the information found in the tomatodiseasecatalogat (http://vegetablemdonline.ppath.cornell.edu. However, in order to be successful and to choosethebestvariety,theraceofFusariumshouldbeknowninadvance;

• Usecroprotation.Growtomatoesinthesamefieldareanomorethanonceinfour years. Lightly infested soilmay become heavily infested by too-frequentcropping of tomatoes;

• In home gardens, pull up and burn wilt-infested plants when they becomeseverelydiseased;

• Fungicides are not effective for controlling Fusarium wilt.

Septoria Leaf Spot

Causal Agent – Septoria lycopersici. Septoria leaf spot is a disease of the leaves andstemsoftomato.Itdoesnotaffectthefruitdirectly.Thediseasecanresultinrapiddefoliation of the plant underwarm andwet conditions.The fungus requireswateron the surface of the plant in order for the spores to germinate and infect. The fungus survives between tomato crops in the soil on infested debris of tomato and weeds. Spores formed on crop debris splash onto foliage and start the disease. Wind and rain spreadsporesproducedbythefungustoadjacentuninfectedleaves.Inthegreenhouse,spores can survive on structures such as bench tops for a limited amount of time. The fungusismostactivebetween15 o and270C, when rainfall is abundant.

DiseaseSymptoms:Symptomsmayappearontheleavesandstemsatanystageofplantdevelopment;however,theyusuallybecomeevidentafterplantshavebeguntoset fruit.Thefirst symptomsaresmall,water-soaked, roughlycircular spotsscatteredovertheleaf.Thesespotsenlargetobecome2to5mmindiameterwithdarkmarginsandtancenters.Small,dark,pimple-likefruitingbodiesinwhichsporesofthefungusareproducedcanbeseen in thecenterof the lesions.Older leavesnear thegroundusually show symptoms first.The diseasemoves up the plant rapidly onto youngerfoliageinrainy,warmweather.Whenleavesareheavilyinfected,theydropprematurely.Exposedfruitsaresubjecttosunscald.Severelyaffectedplantshavepoorlydevelopedfruitwhich become red early and lack sugar content.The funguswhich causes thisdisease can grow on several different weed species.

Figure 6.9 Symptoms of powdery mildew on tomato.Source: Cornell University

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Control

• Use crop rotation. Rotate out of tomatoes for four years and avoid using anysolanaceouscrop(potato,pepper,eggplant)intherotation;

• Sanitation:Remove,burnorburyallplantdebris;

• Growtomatotransplantsinsterilizedsoil;

• Controlweeds,especiallyhorsenettleandnightshade;

• When conditions are favorable for disease development, an effective fungicide sprayprogrammaybenecessary inorder toadequatelycontrolSeptoriaLeafSpot;

TomatoPowderyMildew

CausalAgent – Leveillula taurica and Erysipheci choracearum.Fungi causing this diseaseareanobligateparasiteandcannotsurvivewithoutthelivinghost.Itsurvivesfromcroptocrop in livingweedspeciesor in livingtomatoplantsbetweencrops. Itcannot survive in dead plant debris, and conidia of the fungus that spread the disease bywinddonotsurviveforlongperiodsoftime.Unlikemostotherfungithatcauseplantdiseases,powderymildewfungidonotrequirefreewateronthesurfaceoftheplantinorderforsporestogerminateandinfect.Insteadthefungusrequiresconditionsofhighrelativehumiditytoinfect.Itrequiresrelativehumiditylevelsgreaterthan50percentand the optimum relative humidity for infection is 90 percent and above. Infectioncanoccurbetween the temperatures of 10o to 35oC with the optimum temperature below 30oC(16oto20oC).Powderymildewisusuallymostseriousundergreenhouseconditions;however,itcanbeaseriousprobleminthefieldandingardensonhighlysusceptible varieties.

DiseaseSymptoms:Symptomsfirstappearaslightgreentobrightyellowspotsontheuppersurfaceoftheleaf.Thesespotsusuallydon’thaveverydistinctmarginsandgraduallybecomemorenoticeableas theydevelopthewhite,powderyappearancetypicalofpowderymildews.However,thisiswherethisdiseasediffersfrommostotherpowderymildews thatwe encounter.The powderymildew of tomato is apparentlymuchmoreaggressivethanothermildews.Onceleavesareinfected,theyquicklybrownand shrivel on the plant. This rapid death of infected leaves and defoliation of plants is not typicalofmostmildews.The fungus is readily spread tonearby leavesorplantssinceabundantsporesareproducedandareeasilycarriedbyaircurrentsorproductionactivities in the house.

Control(Greenhouse)

• Maintain adequate row and plant spacing to allow for good air circulationthroughtheplantcanopyinordertoreducerelativehumidity;

• Maintainrelativehumiditylevelsbelow85percent;

• Promotegoodaircirculation,especiallyinplastichouses;

• Lookattheplants(scoutthegreenhouse)fordiseasesymptomsandpruneoutand remove diseased plant tissues (do not carry them exposed through thehouse).Thiscanspreadthedisease;

• Following harvest, all plant debris should be removed and production areas shouldbethoroughlycleanedanddisinfested;

Figure 6.10 Symptoms of seedling damping off. Source: Thoughtyomayskpictures


tomato

• Use resistant varieties;

• Effectivefungicidescanbeveryimportantforcontrollingthisdisease.Fungicidesshouldbeappliedassoonassymptomsarefirstobserved.Earlycontroliscritical.Ifthediseasebecomeswidespread,fungicidesmaynotbeeffectiveforcontrol.

Control(Field)

• Maintain adequate row and plant spacing to allow for good air circulationthroughtheplantcanopyinordertoreducerelativehumidity;

• Stakingupplantsandpruninghelpstoincreaseaircirculationinthecanopyandreducerelativehumidity;

• Lookattheplants(scoutthefield)fordiseasesymptomsandremovediseasedplantsassoonastheyaredetected;

• Usediseaseresistancevarietiesiftheyareavailable;

• Effectivefungicidescanbeveryimportantforcontrollingthisdisease.Fungicidesshouldbeappliedassoonassymptomsarefirstobserved.Earlycontroliscritical.Ifthediseasebecomesverywidespreadandsevere,fungicideswillprobablynotbe able to provide effective control.

SeedlingBlightandDamping-Off(BlackLeg)

Causal Agent – Pythium spp. Rhizoctonia solani, Fusarium spp. Species of soil-bornefungiinthefollowinggeneraarecommonlyassociatedwithseedlingblightanddamping-off:BlackLeg,Rhizoctonia,Pythium,Phytophthora,andFusarium.

Black leg isadiseaseof tomatoseedlings.Thedisease is favoredbywetweatherandhighsoilmoisture (saturatedsoils) in thefieldandhigh relativehumidity in thegreenhouse.Improperspacingofplantsresultingindensevegetationandinadequateventilationarehighlyconducivefordiseasedevelopment.

DiseaseSymptoms:Darkbrowntoblack,sunkenlesionsdeveloponthestematthebaseofyoungtomatoseedlingsatorbelowthesoil line.Thelesionsgenerallygirdlethestem.Infectedplantsdryupanddie.Evenifnewrootsdevelopabovethedamagedarea,plantdevelopmentisgreatlyimpeded.

Control

Select light,well-drained soils.Avoidheavy soils that canbecomesaturatedwithwater.Disinfestgreenhouseand seedbed soilbeforeplanting,using steamorasoilfumigant(e.g.,chloropicrin,Vorlex,methylbromide,etc.)thatiseffectiveagainstsoil-bornefungi;

• Greenhouse structures, benches, containers, used stakes, and tools shouldbedisinfestedandpathogen-free;

• Maintain adequate row and plant spacing to allow for good air circulationthrough the plant canopy in order to reduce relative humidity and provideadequateventilationinthegreenhouse;

• Fungicides and fungicide drenches;

• Cultural control practice.

Figure 6.12 Symptoms of To Mv on tomato. Source: Technico Agricola

Figure 6.11 Symptoms of rhizopus rot. Author: R. Stolonifer

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RhizopusRot(WetRot)

Causal Agent – Rhizopus nigricans. Diseasedamagesbothgreenandripetomatofruit. Optimal conditions for pathogen development are high air humidity and anoptimumtemperaturearound15°C.

Diseasedevelopmentandspreadgreatlyincreasesinsuchstorage,especiallywheretomatoesarestoredimproperlyinthicklayers.

DiseaseSymptoms:Initiallywater-soaked,colorlessspotsdevelopundertheskinonthefruitsurface.Duringthisearlystageofdevelopment, it isdifficulttodifferentiatedamagedfromhealthytissue.After twotothreedays, the innertissues (flesh)of thefruitstarttobreakdown(disintegrate)andturnsintoacolorless,liquidmasswhichhasanunpleasantodor.Fruitskinbecomeswrinkledandcracked.Thisdiseaseespeciallydamages unripe fruit. In conditions of high temperature, damaged green fruits arecompletelydestroyedwithinfivetosevendays.

Control

• Timelycropharvesting.Harvestfruitbeforeitbecomesfullyripe(red);• Properstorageandpost-harvesthandling.Storetomatoesatatemperatureof

lessthan7°C;• Sanitation isvery important.Storageareasandcontainers shouldbeproperly

disinfested after use.

TomatoDiseasesCausedbyVirusesTobacco(Tomato)MosaicVirus(ToMv)

Causal Agent – Tomato Mosaic virus. Is the same as tobacco mosaic virus andis extremely infectious, being spread easily by persons touching a healthy tomatoplant after touching an infected plant. Plant to plant contact during pulling out of young seedlings, transplanting, cultivating, weeding, and wind-whipping of theleavesareotherverycommonwaysofspreadingthevirus.Handoperations,suchaspruning, tying, pollinating, spraying, watering, and picking fruit are also importanttent transmission, especially in greenhousegrown tomatoes.This secondary spread,very common ingreenhouses about 10weeks afterplanting, canoccur very rapidlyonce inoculums is available from plants infected in the seedling stage. The time from mechanicalinoculationofleavestothedevelopmentofsymptomscanbeasshortasaweek,andnewlyinfectedplantsareareadysourceofvirusforadditionalspreadevenbefore symptoms are evident. In a greenhouse, earliest symptoms commonly occurnear entrances, sources of water, and other service areas. The most rapid spread occurs alongrowsduetomechanicalspreadbyworkers.

Disease Symptoms: Light and dark greenmottled areas,which are usually somewhat raisedandpuckered,deveop in the leaves.Theyoung leavesat the tipsof thegrowingshootstendtobunchandunfoldunevenly.Plants infectedwhenyoungarecommonlystuntedandhaveayellowishcast.Leafletsonyoungplantsgrowingunderglassorplasticareoftenlong,pointed,andnarrow.Symptomsappearabout10daysafter the plants become infected.

Stemstreakingcanbecausebyoneormorevirusstrains.Thestreaksaredarkandlongitudeinalandmaybeshortorlong.Affectedstemsarebrittle,easilybroken,andcontainbrownareasinthepithandcortex.

Figure 6.13 Symptoms of INSV on tomato Source: Thoughtyomaysk pictures


tomato

Ordinarilythefruitdoesnotshowanymarkeddisfiguration.Boththenumberandsizeofthefruitarereduced,however,resultinginonlyabouthalftheyieldofhealthyplants. The earlier plants become infected, the greater the loss. Occasionally fruitmottling,bronzing,andinternalbrowningdevelop.Distinctmottlingisassociatedwithseverestrainsofthevirus.Thesymptomsmaybemaskedinhotweather,buttheplantsremaininfected.Thesymptomsreappearwhencool,cloudyweatherreturns.

TomatoImpatienceNecroticSpotVirus(INSV)

CausalAgent–TomatoImpatienceNecroticSpotVirus.Istransmittedfromplanttoplantprimarilybywesternflowerthrips(thereareseveralotherspeciesofthripswhichcan also transmit these viruses).Thrips acquire the virus as larvae andonly transmitduring the adult stage. An adult thrips can infect a plant with the virus after feeding for only30minutes.

DiseaseSymptoms:INSVcausesawidevarietyofsymptomsincludingwilting,stemdeath,stunting,yellowing,poorflowering,andsunkenspots,etches,orringspotsonleaves.Symptomsarenotveryspecificorconsistent,andmerelytell thegrowerthatthereissomethingwrongwiththeplant.Manyotherdiseasesandplantproblemscancause symptoms that resemble INSV.Virus symptomsmay depend on time of year,typeofplant,ageofplant,plantphysiologicalstate,growingconditionsatthetimeofinfection, and strain of virus.

Positive diagnosis is made through the use of either inoculating special indicator plants or chemical tests to determine if the virus is present.

Tomato Stolbur

Causal Agent – Stolburiscausedbyaphytoplasma,whichessentiallyisabacteriumwithoutacellwall.Thediseaseusuallyappearsduringperiodsofhighsoiltemperature.Disease is transmittedby insects. InGeorgia, thedragonflyHyalestes mlacosewichi is considered to be the most important insect vector.

Disease Symptoms: In general, three main types of symptom are distinguished:flowerchanges,prematurewilting,anddeathwithoutobviousflowerchanges.however,symptomsmaybeabsentorhardlydistinguishable.Moreover,theywillvarywiththestolbur strain, environmental conditions and host resistance.

Leaves developed before infection become greenish-yellow, especially at themargins, which may roll up ward. Newly formed leaves become more yellow andaresmaller.Stemsbecomethinattheapexesgrowthisstopped,butenlargedattheinfection sites as a result of abnormal phloem formation. This appears as a greenish, water-soakedbandone to twommwide,which extends towards the xylem. Lateralshootsdevelop,givingtheplantabushyaspect.Flowerbudsassumeanabnormallyerectposition,thesepals,whoseveinsdevelopavioletcolor,remaincompletelyjoinedandthecalyxisenlargedandcyst-like(“bigbud”).

Flowers,ifalreadyformedwheninfectionoccurs,becomesimilarlyerect,andmaybesterile, andpetals aregreenish insteadof yellow.Distortion is common, andpetals ofyoungflowersbecome totallydwarfed andgreen. Peduncles are thicker thannormal.Fruitdevelopment isarrested following infection.Green fruitsalready formedbecomesolid,dryandcolorveryslowly.Necrosisoccursattheembryoniccenterinyoungerfruits.Pedicelsoffruitsarethickerthaninhealthyplants,inspiteoftherelativelysmallfruitsize.

Figure 6.14 Symptoms of stolbur on tomato.Source: Phytoplasmas data base

Figure 6.15 Symptoms of bacterial canker on tomato. Author: T.A Zitter

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Control

• Always start the plantingwith healthy seeds or transplants, Seeds should betreatedinadvancein20percenthydrochloricacidfor30minutesorintheonepercentsolutionofpotassiumpermanganatefor20minutes.(Iftomatoseedisproducedbyacompany, insuchcase itwillalreadyhaveundergoneanti-viralprocedures);

• Contaminated soil in greenhouses must be replaced with uncontaminated soil, on which no tomato, pepper and other solanaceous crops have been produced. Itcanalsobesteamtreatedatthetemperatureof90 oto100°C,foronetotwohours;

• Identificationanderadicationof insectvectors,aswellas timely identificationand removal of diseased plants are of great importance. It is necessary tomonitorplants in thegreenhouseandfieldat leastonceaweek. Immediatelyupondiscoveryof insectvectorsordiseasesymptoms,diseasedplantsshouldberemovedandhealthyplantstreatedwithaninsecticidetocontroltheinsectvectors.Replacingdiseasedplants(afterremoval)withhealthyplantsshouldnotbeconductedearlierthantwotothreedays.Diseasedplantsshouldbeplacedinspecialcontainersaftertheyareremoved.Thesecontainersshouldbedisinfestedperiodically.Generalviruscontrolmethodsalsoinclude:disinfestingworktoolswith a five percent solution of potassium permanganate, weed management within and near the planting, and conducting proper production practices for tomatoes such as appropriate irrigation and fertilization and optimal plant and rowplacement.Ingreenhouses,itisnecessarytoregulateairtemperatureandhumidity,aswellassoilmoisturecontent.Bringingdecorativehouseplantsintothegreenhouseshouldneverbepermitted,sincetheymaybeareservoirforthevirus and become a source of infection;

• Productionofvarieties/hybridsresistanttoviraldiseasesisanimportantfactor;

• Itisinadmissibletobringintogreenhouses,wheretomatoesaregrown,thesoilonwhichpotatoesorothersolanaceouscropshavebeenproduced.Forseed-production purposes, it is not recommended to use the fruit which has been pickedfromplantswithviraldiseasesymptoms.

TomatoDiseasesCausedbyBacteria Bacterial Canker of Tomato

Causal Agent – Clavibacter michiganensis. BacterialcankeriscausedbyClavibacter michiganensis .sub sp. speck pathogen. It has the ability to infect tomato plantssystemically.Itisseedborneandcansurviveoninfestedplantdebrisinsoil.Bacterialcanker is a severe disease that is wide spread and can cause localized epidemics during warm, moist conditions. Optimal conditions for bacterial spot and canker are highmoisture,highrelativehumidityandwarmtemperatures(75o to90oF).

Disease Symptoms: Primary or systemic symptoms of bacterial canker (frominfectionsoriginating inseedsoryoungseedlings) includestunting,wilting,vasculardiscoloration, development of open stem cankers, and fruit lesions. When affected stems aresplitopenlengthwise,athin,reddish-browndiscolorationofthevasculartissueisobserved,especiallyatthebaseoftheplant.Onyoungseedlings inthegreenhouse,lesionsmayappearasraisedpustulesonleavesandstems.Theseplantsrarelysurvive

Figure 6.16 Symptoms of bacterial wilt in tomato plant. Source: Invasive Organisation


tomato

theseasoninthefield.Secondarysymptomsinthefieldincludeleaf“firing”(necroticmarginalleaftissueadjacenttoathinbandofchlorotictissue)andfruitlesions.Spotsonfruitarerelativelysmall(3to6mm)surroundedbyawhitehalo(“bird’s-eye”spots).Canker bacteria may also invade internal fruit tissues, causing a yellow to brownbreakdown.

Control

• Rotate tomatoeswithnon-solanaceous cropswith at least two to three yearsbetween tomato crops. Avoid rotation with peppers, which areal so susceptible to bacterial spot;

• Plantonlyseedfromdisease-freeplantsorseedtreatedtoreduceanybacterialpopulations. Treatments include fermentation of tomato pulp and seeds at room temperatureforfourtofivedays;

• Somedecreaseingerminationmaybeexpectedfromthesetreatments;

• Useonlytransplantsfreeofdiseasesymptoms;

• Carry out proper sanitation of transplant production green-houses. Removeall weeds and plant debris, clean all tools with disinfectant solution, and wash handsthoroughlybeforeandafterhandlingplants.Waterplantsearlyinthedaytoreducetheamountoftimefoliageiswet.Donothandleplantswhentheyarewet.Aftereachcrop,cleangreenhousewalls,benches,etc.,withhotsoapywater,followedbythoroughrinsingandtreatmentwithadisinfectant.Ifpossible,closeup greenhouse after transplant production is completed to allow natural heating duringthesummer.Useonlynewplugtraysandpathogen-freeplantingmixes.Avoid growing peppers and tomatoes in the same greenhouse unless pepper seedhasalsobeentreatedasinstep2;

• In the field, control irrigation to minimize the time foliage is wet and avoidworking among wet plants to minimize spread of disease.

Tomato Bacterial Wilt

Causal Agent – Ralstonias olanacearum. The bacteria can overwinter in soil. Thepathogencanoccur innewly-cleared landaswell as in areaswhere susceptiblecrops have not been grown. The bacteria often enter a field on infested transplants or equipmentorthroughdrainagewater.Bacteriainfectplantsthroughtherootsorstems,most oftenwhere tissue has been injured by cultivating or by some other physicalmeanssuchasnematodes.Thedisease ismostcommonlyfoundin low,wetareasoffieldsandismostactiveattemperaturesabove25°C.

DiseaseSymptoms:A characteristic of this disease, which sets it apart from other wilt diseases,isthatplantswiltanddierapidlywithoutyellowingorspottingofthefoliage.Bacteriacausewiltby invadingandgraduallyblocking thevascular tissue (the food-andwater-conductingvesselsjustbeneaththeepidermis).

Toidentifybacterialwilt,cutandpeelbackasectionoftheepidermisandcorticaltissue(bark)justabovethesoilline.Intheearlystagesofbacterialwilt,thepith(centerof thestem)willappearwatersoaked; later, thepithwill turnbrownandsometimesbecome hollow. The discoloration of the pith distinguishes this disease from Fusarium and Verticillium wilt.

Figure 6.17 Symptoms of bacterial spot on tomato. Source: Plaza Education

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Anotherrelativelyeasydiagnostictechniqueistocutaportionoftheaffectedstemandplaceitinaclear-sidedglasscontainerfilledwithwater.Watchforawhite,milkyoozestreamingoutof thecutendof thediscoloredvascular tissue.Thewhite,milkyooze is diag nostic for this disease.

Control

• Usecroprotation.Growsusceptiblecrops(peppers,potatoes,andeggplant)inthesameareanomorethanonceeveryfouryearstoreduceinoculuminthesoil;

• Usesoilfumigationinheavilyinfestedfields;

• In the home garden, rogue (weed out) wilted plants and remove the soilsurrounding their roots to reduce spread of the dis ease;

• Disinfectinfestedsoilwithsoilsolarization;

• Controlhumidity,moistureandtemperatureinthegreenhouse;

• Sanitation;removeanddestroyinfectedplantdebris;

• Alwaysstarttheplantingwithdiseasefreeseedsortransplants;

• When available, use disease resistant varieties.

Bacterial Spot of Tomato

Causal Agent – Xanthomonas campestri. spv. Vesicatoria. Bacterial spot can be a severe disease of tomato that can cause epidemics during warm, moist conditions. Bacterial spot can cause moderate to severe defoliation, blossom blight, and lesions on developing fruit. The bacteria can survive on the surface of infested seed and has been shown to survive on plant debris in the soil.

DiseaseSymptoms:Onimmaturefruit,bacterialspotlesionsaresmall(3to6mm)water-soakedspotsthatbecomelightlyraisedandenlargeduntiltheyareabout3to8mminchindiameter.Thecentersofthesespotslaterbecomeirregular,lightbrown,slightlysunkenwitharough,scabbysurface. Intheearlystagesof infection,awhitehalomay surroundeach lesionatwhich time it resembles the fruit spotofbacterialcanker. Ripe fruit become resistant to infection.

Control

• Rotate tomatoeswithnon-solanaceous cropswith at least two to three yearsbetween tomato crops. Avoid rotation with peppers, which areal so susceptible to bacterial spot;

• Plantonlyseedfromdisease-freeplantsorseedtreatedtoreduceanybacterialpopulations Treatments include fermentation of tomato pulp and seeds at room temperatureforfourtofivedays;

• Somedecreaseingerminationmaybeexpectedfromthesetreatments;

• Useonlytransplantsfreeofdiseasesymptoms;

• Carry out proper sanitation of transplant production green-houses. Removeall weeds and plant debris, clean all tools with disinfectant solution, and wash handsthoroughlybeforeandafterhandlingplants.Waterplantsearlyinthedaytoreducetheamountoftimefoliageiswet.Donothandleplantswhentheyarewet.Aftereachcrop,cleangreenhousewalls,benches,etc.,withhotsoapywater,


tomato

followedbythoroughrinsingandtreatmentwithadisinfectant.Ifpossible,closeup greenhouse after transplant production is completed to allow natural heating duringthesummer.Useonlynewplugtraysandpathogen-freeplantingmixes.Avoid growing pepper sand tomatoes in the same greenhouse unless pepper seedhasalsobeentreatedasinstep2;

• In the field, control irrigation to minimize the time foliage is wet and avoidworking among wet plants to minimize spread of disease.

PhysiologicalDisordersNon-pathogenicdisorders, alsoknownasPhysiologicaldisorders, aredisease like

symptomsthatarecausedmostlyby impropertemperature,humidity,nutrient,and/orwater. Examples of physiological disorders affecting tomato are blossom-end-rot,catface,yellowshoulder,graywall,fruitcracking,chillinginjury,andseveralothers.Inthischapterwewillcoverblossomend-rot,catface,andyellowshoulder.

Causal factors – Calciumdeficiencyinthefruitisthemaincausalfactor.Calciumisoneofthemajorcomponentsofthecellwall.Extremesoilmoistureconditionseitherdryorwethinderstheabilityoftheplanttotakeupadequateamountsofcalciumintothecanopyandthefruit.TheseconditionsresultinadeficiencyofCaavailabletothematuring fruit, at the locationwhere thedamagebecomesapparent.Thedeficiencyis more apparent during the critical phase of early fruit growth. Other factors thatcontributetomoreincidenceofblossomendrotareapplicationofexcessammonium,K, and Mg, which are known to interfere with Ca uptake and enhance more vegetative tissue, which can out compete the fruit for calcium reserve.

DiseasesSymptoms:Blossom end rot starts as a small water soaked spot at the lower endofthefruitandcontinuestoexpandasthefruitincreasesinsize.Inseverecases,more thanhalf the fruitmay turn light todarkbrownand theskin texturebecomesleatheryasthefruitages.Thedisordercanalsocausesecondaryinfectionbymoldsandbacteria.Affectedfruitsripenprematurely,butthefruitisunmarketable.Thedisorderusuallyaffects thefirst fewdeveloping fruits,especially those thataregrown incoldsoilsandexposedtoerraticwateringregimes.

Control

• AdjustsoilpHtoabout6.8;

• Addnon-dolomitelimetoacidsoils;

• SprayfruitswithCa,especiallyduringthefirsttwoweeksoffruitgrowthandthelast two weeks before harvest;

• Avoidoverfertilizationwithnitrogen,especiallyammoniaformulations;

• Avoid ions imbalance in soil;

• Avoidfluctuationsinsoilmoistureandwaterlogging;

• Avoid practices that cause root pruning;

• Whenpossible,avoidcultivarspronetoblossomendrotlikeRomatypes.

Figure 6.18 Symptoms of blossom end rot of tomato. Source: New York State University

Figure 6.20 Symptoms of yellowshoulders in tomato. Source: eorganics

Figure 6.19 Symptoms of catface in tomato. Source:Gardening Know How

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Catface

Causal Factors – Thedeformityiscausedbyacombinationofinternalandexternalfactorsthatoccurduringdevelopmentoftheflowerresultinginthefruitnotdevelopingnormally.Catfacemaybecausedbyabnormallycoolorhotweatheroranydisturbancetoflowerpartsduringblossoming.

Symptoms

Thedefectisusuallylocatedontheblossomendofthefruit.Catfaceiscommonlyobservedinfirstharvestfruits.Thesymptomsincludeenlargedscarsandholesintheblossomend.Coldweatheroccurringaboutthreeweeksbeforefloweringbeginshasbeenidentifiedasoneofthecauses.Coldweatheralternateswithhot,andthesecyclesare a predisposing factor for tomato catfacing.

Control

• Plantvarietiesthathistoricallyhavehadlittleproblemwithcatfacing;

• Removefruitsshowingthesymptomassoonasitappears.

yellowShoulder

Causal factors – Severalcausal factorshavebeencited to induceyellowshoulderincluding environment, specifically high temperature above 90°F, cultivar, and virus.Studieshavealsoshownthatthisdisordercanbetriggeredbyinsufficientpotassium,excessmagnesiuminrelationtocalcium,andsoilpHabove6.7.

Symptoms

Thedisorderischaracterizedbywhitetoyellowregionsundertheskin,aroundthestemend,thatshowthroughandreducethequalityofthefruit.Thedisordercanrangefromverymildwithsomeinternalspottingtoquiteseverewithlargehardenedareas.

Control

Growersneedtobeawarethatyellowshoulderisnotadelayintheripeningofthefruit,butanactualdisorder.Thedisorderoccursduringearlystagesoffruitdevelopment,whichmakestissueanalysis,especiallyduringearlybloom,extremelyimportant.

• Insure that thepotassium level in leaf tissue ishigher than3%bydryweight,especiallywhenthefruitdiameterislessthan3cm;

• AdjustsoilpHtobetween6.4and6.7;

• Increasethemagnesiumtocalciumratiointhetissuetoaboutonetofour;

• Plant less susceptible varieties;

• Croprotationreducestheincidenceofyellowshoulder;

• Fruitsthathaveyellowshouldershouldberemovedassoonaspossibletosaveenergyfortheremainingfruits;


Carrot (Daucuscarota var. sativus) is amember of theUmbelliferae family,whichincludesanise,caraway,celery,coriander,dill,fennel,parsley,andparsnip.Carrotisoneofthemostwidelygrownandconsumedvegetablesintheworld.Carrotsareproducedfor a variety of uses including freshmarket and processing. The largest percentageofcarrotsproducedaroundtheworld is for freshmarketsaleseitheraspeeledbabycarrots,carrotsticks,shreddedcarrots,and/orsaladmixes.Carrotsarealsoproducedforprocessing,whichincludesbabyfood,frozen,andcannedproducts.Oneofthereasonsforthewidespreadpopularityofcarrots is thattheyareamajorsourceofVitaminA.Theyarealsorichinothervitamins,minerals,andfiber.Carrotsarepopularsnacks,usedinsalads,cookedaspartofmaindishes,andanumberofotherculinaryuses.

ClimaticRequirements.

youngcarrotplantsareverysensitivetofreezingtemperatures,howevertheycantolerateshort-termexposure to frost.The ideal temperature forcarrotsplantgrowthisintherangeof100to270C. Carrot plants grown under higher temperatures develop misshapedroots.Plantsgrownunder lowertemperaturesmaygrowveryslowly,andthe roots will be long, slender, and have lighter color and sugar content. Carrots with arootlessthan2cmindiameteraremoresusceptibletocoldinjurythanplantswithlarger roots.

Carrotsareclassifiedasabiennialcropwithfloweringstalksforminginthesecondseason.However,insomeareascarrotscanflowerprematurelydependingonweather.Inmanyareasfreshmarketscarrotsareplantedinlatesummerandharvestedinearlytolatefallofthesameyear.However,plantingcarrotsforseedproductionusuallystartsinearlyfallandseedsareharvestedinearlytomiddlespringofthefollowingyear.Forthisreason, carrots grown for seed production are planted in areas with mild winters. The idealweatherconditionsforfloweringarecoolwinterdaysfollowedbylongerspringdays.Inmostyears,floweringrequiressixtoeightweeksoftemperaturesbelow100C. Warmtemperatureatplantinginthefallisnotdamagingtotheplantsiftheyarewellwatered. Carrots tend to produce a higher percentage of seed stems as the weather warms up during the spring and summer.

Small carrot seedlings up to six leaves cannot withstand hard freezes but aresomewhatfrosttolerant.Optimumtemperaturesareintherangeof150to21oC, with daytimehighsof24oCandnighttime lowsof13oC. Although the crop can be grown outsidethisrangewithlittleornoeffectontops,temperaturesdifferingdrasticallyfromtheabovecanadverselyaffectrootcolor,texture,flavor,andshape.Lowertemperaturesfrom this rangemay induce slowgrowth andmake roots longer,more slender, andlighter in color. Carrots with a root less than one inch in diameter are more susceptible tocoldinjurythanlargerroots.Longexposuretohotweathermaysuppressgrowthandyieldandinseverecasescaninjureorkillyoungplants.Additionally,diseaseinfectionisenhanced as temperatures warm up in late spring and summer.

Carrotsneedanamplesupplyofmoisturefromrainfalland/orirrigationthroughoutthegrowingseasonsincetheyarenotdroughttolerant.Aconsistentmoisturesupplyhelps keep the crop growing and reduces the incidence of splitting from growth flushes.

Althoughtechnicallybiennialinnature,carrotscanproduceseedstemsprematurelyinGeorgia.Thisiscommonlyknownasbolting.MostcarrotproductioninGeorgiaoccursduringthefallmonths,throughwinterandintospring.Coolwintermonthsfollowedby

Carrot

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increasingdaylengthinspringcanresultincarrotsbeingexposedtoconditionsthatinduceflowering. Flower induction in carrots requires aperiodof six toeightweeksoftemperaturesbelow100C.Increasingdaylengthacceleratesflowerinduction.Onceflowering is initiated, the seeds talk elongates rapidly, particularly as temperaturesincrease.Althoughfallheatatplantingisnotinjuriousiftheyarewellwatered,carrotswill tend to produce a higher percentage of seed stems as spring warming turns into summer heat. Carrots that have produced seed stems are not marketable.

SoilRequirements

Thetypeofsoil influencestheshape,size,andtextureoftheroots. Ideally,sandyloamsoiltoloamsoil,freeofstonesandwithpHintherangeof6.0to6.5isbestforgrowing carrots. Heavier and lighter soilmay be used if they are keptmoist. Rootsgrowninheaviersoilstendtobeshortandblunt,whilerootsgrowninsandyloamsoilsproducelong,smooth,andstraightroots.Soilswithexcessiverocksproduceforkedormisshapen roots.

Varieties

There are four basic groups of carrots withmany varieties available within eachgroup.

1. Chant nay group. This group tends to have tapered roots with a blunt or roundedend.Therootsareabout1.0to1.5cmindiameterandabout12to16cmlong.Therootcolorismostlylightorangewithaslightlyredcolorationinthe core of the root. This group serves a dual purpose for processing and fresh market.

2. Imperator andDanvers group. Imperator is themostwidely growngroup forfreshmarket.The average root diameter is about 3 to 4 cm and the averagelengthisabout15to25cm.Thisgroupstoresverywellincoldstorage.Largerrootstendtobecomewoodyintexturewhiletheyoungerrootshaveexcellenttexture.Danverssub-grouphasdeeporangewithlightlycoloredcenterandtheyaresimilarinsizeandtexturetoImperator.

3. Nantes group. This group is the most popular group for fresh market. Carrots in thisgrouptendtohavecylindricallyuniformrootsfromthecrowntothetip.Theaveragerootdiameteratthecrownisabout4cmandtheaveragerootlengthisabout16to18cm.Therootsurfaceissmoothandthefleshisbrightorange,withaverysmallcore.

4. The Amsterdam group. This group is grownmostly for freshmarket and it isconsideredveryeasytogrow.Thefleshisbrightorange.Therootsareabout15cmlongandhavearoundendthatextendsintoaroothairbeyondthefleshypart. This group can be grown in protected structures or outdoors.

Seedingrates,fertilitymanagement,andweedcontrol.

Worldwide,carrotsareproducedbydirectfieldseeding.Usuallytwocropsaregrowneachyear;one inthespringandtheother in theautumn.Autumnproducedcarrotsusuallyhavebettereatingqualityanduniformrootsizethanspringcarrots.


Carrot

Carrotaregrownonhillsorflatgroundwithseedsspacedatabout5to7cmapart.Idealplantpopulationsareintherangeof1.1millionplantsperhectareforfreshmarketcarrots and 750,000 plants for processing carrots. Planting on raised beds has theadvantage of good soil drainage.

Fertilitymanagementincarrotshasacriticaleffectonrootquality.Although,carrotshaveamediumrequirementfornitrogen,itisadvisedthatthenitrogenratebedividedinto six to seven equal applications during the season. Themaximum amount thatshouldbeincorporatedperapplicationshouldnotexceed16kgperhectare.Thissplitapplicationallowsforadequateroottotopbalanceandreducesthepotentialforrootsplitting as a result of growth spurts.

For other nutrients, broadcast one-third to one-half of potassium and all of thephosphorousprior toplanting. If raisedbedsareused,band in thewidthof thebedthen incorporate into the soil prior to planting. The remaining potassium should be appliedintwotothreeapplications.Additionally,apply11kgzinc,1kgofboron,and11kgofsulfurperhectarepriortoplanting.

Controllingweeds incarrots,especiallywhentheplantsareyoung isverycritical,because carrots are considered weak competitors with weeds. Proper tillage and herbicide applications to control perennial weeds will reduce competition.

Storage and postharvest handling

Careful harvesting to reduce root damage is very important for extending thestoragelifeofcarrots.Damagetothemainrootortothecuticleoftenresultsinrapiddeterioration of quality. Carrot leaves (tops) are very sensitive to low temperaturestorage;below6oC,however,carrotrootskeepbestwhenstoredat-1oC. When cold stored,carrottopsareoftenremovedinordertoincreasetherootshelf-life.Duringshipping carrot roots are often covered with ice in order to reduce their respiration rate.

CARROTDISEASESCarrotshaveseveraldiseasesthatcanbeveryseriousunderenvironmentalconditions

that are conducive todiseasedevelopment.Diseasesof carrots are causedby fungi,virusesandbacteria.Mostcarrotdiseasesarecausedbyfungi.Themaindiseasesthatarecausedbyfungiinclude:BrownRot;BlackRot(blackcarrotrootdieback);CottonyRot;GrayMoldRot;CraterRot;andFusariumDryRot;ThemostimportantdiseasescausedbyvirusesincarrotsareParsnipyellowFleckVirusandCarrotRedLeafVirus.ImportantdiseasescausedbybacteriaareBacterialSoftRotandBacteriosis.

Duringthefirstyearofdevelopment(productioninthefield),carrotshaverelativelyfewdiseaseproblem.DuringthesecondyearofproductionBlackRot,BrownRotandCraterRotarediseasescausedbyfungithatcanbecomeseriousintheproductionfield.Themajorityofdamageandyield losses tocarrotscausedby fungaldiseasesaretaprootrotsthatoccurduringstorage.Itshouldbenoted,thatdamagecausedbytaprootrotsinstorage(mainlyCottonyRotandGrayMoldRot))canrangefrom30to70percentcrop loss.

Figure 7.1 Symptoms of carrot brown rot. Source: WikiGardener

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CarrotDiseasesCausedbyFungi Carrot Brown Rot

Causal agent – Phoma rostrupii.BrownrotisprimarilyproblemoncarrotinRussiaand surrounding countries. It is considered one of the most important seedbornediseasesofcarrotintheUkraine.Thediseasedamagesthestalk,spadix,flowers,stemsandtaprootofcarrot.Themajorityofdamagecausedbythediseaseoccursduringthesecondyearofproduction.Thecausalfungusoverwintersininfestedplantdebrisinoron top of the soil and is seed borne. The optimal temperatures for the development of fungalsporesare20°to25°C.Whenthetemperatureisbelow10°C,sporedevelopmentisreduced,andwhentemperaturesrangefrom0°to3°C,sporedevelopmentprogressesextremelyslowlyorstops.

DiseaseSymptoms:Darkbrownspotsappearonabove-groundpartsoftheplant(stalk, branches, spadix and seed). These spots later turn violet and exude a stickysubstance.Inhotweather,diseasedtissuesbecomecoveredwithblackfungalfruitingstructures(pycnidia).Infectedtissuesdryandbreakeasily,andtheleaveseventuallydie.

Taprootdamagemostfrequentlybeginsfromthefoundation.Damagedtaproottissuesaredarkbrownanddry.Diseasesymptomsarelesspronouncedinautumnandmore visible during winter storage periods. At this time, the tap root foundation rots, whilesunkengrayishspotsappearonitssurface,underwhichthetissuedisintegrates,dries and develops cracks.

Control

• Use proper agricultural production techniques that minimize damage to theplant and to the root and results in healthy vigorous plants. Handle plantscarefullyduringharvestandpacking topreventdamage.Useproper levelsofnitrogen fertilization;

• Careful and thorough cleaning and disinfesting of storage areas;

• Croprotation-usearotationthatexcludestheproductionofcarrotsforatleasttwotothreeyears;

• Sanitation-removeanddestroyinfectedplantpartsinthefieldandinstorage;

• Applications of an effecting fungicide can be important for controlling this disease;

• The disease is seed borne so effective fungicide seed treatments are recommended.

BlackRot(BlackRootDieback)

Causal agent – Alternaria radicina.Thecausalfungusiscommonlyseedborneandsurvivesininfestedcropdebris(residues). Itcanalsosurviveinsoil intheabsenceofdebris for at least eight years. The fungus produces micorsclerotia that function assurvival structures in soil.

Black rot is an important storage disease of carrot, but can also cause seedling damping-offandleafandcrowninfectionsinthefield.Thisdiseasemainlyaffectstaprootcrops,whicharedamagedmechanicallyorbythecarrotfly.Mechanicaldamage,whichoccursduringtransportationorharvesting,evenifitisunnoticeable,significantly

Figure 7.2 Symptoms of black carrot root dieback. Source: WikiGardener


Carrot

contributes to disease development. The causal agent is a fungus which likes warm temperature.Optimaltemperatureforitsdevelopmentis25°to28°C,withprolongedwetperiodsandrelativehumidityof85to100percent.However,itcanalsodevelopinconditionsoflowertemperatureandhumidity.

DiseaseSymptoms:Thediseasecanaffectallorgansofcarrotplants,atanystageof their development: emerged plants, foliage, tap root, flowers and seed. Initialsymptomsaresmall,brownleafspotsthathavechlorotic(yellow)halosormargins.Spots later develop into dark brown or black lesions at the base of the leaf petiole. Whenthespandexorflowersareinfected,symptomsaremanifestedasblackvelvetyspotsontheleaves.Thefungusmovesfromtheleavesontotheseed.Infectedseedsblackenandoften lose theability toemerge.Emergingseedlings thatare infectedshowweakeningandblackeningofthecrownsandupperroots. Inthefield,crownlesionsusuallyconsistofblacklesionsthatextendbelowthesoilline.Secondaryblacklesionsalsodeveloponthetaproot,especiallyifsplittingorothertypesofdamagearepresent.Inpostharveststorage,thefunguscausesdry,black,sunkenlesionsthathavesharplydefinedmargins.

Theblacklesionspenetrateintothetaprootpulpapproximately0.5-1.4cm.Blackrotischaracterizedbytheexistenceofadarkbrownpowderonthesurfaceofthespots.Thehigherthehumidity,themoreoftensuchpowdercanbeobserved.Roottorootspreadcanoccurrapidlyduringprolongedstorage.

Whenthespandexorflowersareinfected,symptomsaremanifestedasblackvelvetyspotsontheleaves.Thefungusmovesfromtheleavesontotheseed.Infectedseedsblackenandoftenlosetheabilitytoemerge.Plantsthatemergefromdiseasedseedsoftendampen-offanddie.

Control

• Use proper agricultural production techniques that minimize damage to theplantandtaprootandresultsinhealthyvigorousplants.Handleplantscarefullyduring harvest and packing to prevent injury. Use proper levels of nitrogenfertilization;


• Croprotation-Usearotationthatexcludestheproductionofcarrotsforatleastthreetofouryears,orlonger;

• Sanitation-removeanddestroyinfectedplantpartsinthefieldandinstorage;

• Applications of an effecting fungicide can be important for controlling this disease;


CottonyRot(WhiteMold)

Causal agent – Sclerotinia sclerotiorum. Thediseasedamagescarrot,parsley,beans,cabbageandcropsinthecucurbitceaefamilyprimarilyduringstorage.Themainsourceof the fungus is the soil.The fungusproduces survival structures (sclerotia) that cansurviveinthesoilformanyyears.Ascarrotsareproducedonthesamelandplotforyearafteryear,thepopulationofthefungusinthesoilincreasesandthediseasecontinuesto getworse.The fungus spreads intensively in storage areaswhere air humidity is

Figure 7.3 Symptoms of cottony rot. Source: WikiGardener

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high. Temperature has no special significance for development of this disease, since the causalagentcandevelopintemperaturesrangingfrom0°to30°C.Themostoptimalconditionsfordevelopmentofthisdiseaseareairrelativehumidityof95to100percentandtemperaturesof15°to22°C.Lossesinstoragecanbeveryhighbecauseofextensivespreadofmyceliumfromroottoroot.

Disease Symptoms: The first symptoms are small, 5-10 mm in diameter, water-soaked,brownlesionsonleaves,crowns,ortheupperexposedshouldersoftaproots.Whitemyceliagrowthofthefunguscanbefoundonoldordeadleavesandotherpartsofthecarrotwhensoilmoistureandhumidityishigh.Asthepathogendevelops,thewhitemyceliumproducessmallmoundsofmyceliathatbecomehard,blacksclerotia.Infectionof leavescan leadto root rots in thefield.Therootsdevelopasoft rotandsclerotiaareproducedonandaroundthetaproot.Onstoredroots,thefungusproducesextensive,fluffywhitemycelium,andtissuesbeneaththemyceliumbecomessoftandrotted.Themyceliumcanspreadrapidlyfromroottorootspreadingthedisease.

Control

• Use proper agricultural production techniques that minimize damage to theplantandtaprootandresultsinhealthyvigorousplants.Handleplantscarefullyduring harvest and packing to prevent damage. Use proper levels of nitrogen andespeciallyphosphorousfertilization;

• Observeoptimalstorageconditions(temperature:1°to2°C,relativeairhumidity:80to85percent);


• Croprotation-usearotationthatexcludestheproductionofcarrotsforatleastthreetofouryears,orlonger;

• Sanitation- removeanddestroy infectedplantsandtaproots in thefieldandespeciallyinstorage;


GrayMoldRot

Causalagent–Botrytiscinerea.Thecausalfungusisasaprophytethatcancolonizedeadordyingtissuesofmanyplantsspecies. It isacommonpost-harvestpathogenon many fruit and vegetable crops world-wide. It survives as sclerotia in infectedplantdebrisontoporinthesoil.Itcanalsosurviveinthesoilintheabsenceofplantdebris and on various surfaces in storage and packing facilities. Leaves and petioles can be infected in the field, but do not cause much damage in the field. However, field infections provide a source of inoculum for the disease in storage. The fungus enters andrapidlycolonizeswoundsonthetaprootmadeduringharvestingandhandlingorthroughtissuesdamagedbycoldtemperaturesduringstorage(-1°Canless).Thefungusmay also penetrate tissue directly. Freewater on the surface of the plant promotesinfection.Fungusgrowthisslowedbylowertemperatures,butmaycontinueevenattemperatures close to freezing. In storage the fungus canmove fromplant to plantasmyceliumoroverdistancesasair-borneconidia.Graymoldisseldomaprobleminmodern, refrigerated storage and packing facilities.

Figure 7.4 Symptoms of gray mold rot. Source: Integrated Pest Management: RPD No. 942


Carrot

DiseaseSymptoms:Oncarrot,graymoldcandeveloponanypartofthetaproot.Firstsymptomsarewater-soaked,lightbrownortanlesions.Diseasedareaseventuallybecomesoftandgrayincolor.Underconditionsofhighhumidity,thefungusproducesmycelium and conidia that cover the diseased areas with a layer of gray powderygrowth.This iswherethediseasegetsthename,graymold. Irregularlyshaped,hard,blacksclerotiaoftenformindiseasedtissue.Eventually,theentiretaprootmayrot.

Control


• Maintainoptimalstorageconditions(temperature:1°to2°C,relativeairhumidity:80to85percent);

• Sanitation - Careful and thorough cleaning and disinfesting of storage andpacking areas;

• Sanitation- removeanddestroy infectedplantsandtaproots in thefieldandespeciallyinstorage.

Crater Rot

Causal agent – Rhizoctonia carotae. Crater rot is a disease that occurs on carrot in storage.Thediseaseismostcommonwhencarrotsareplacedinlong-term(onemonthormore)refrigeratedstorage.Croplossesofupto10percenthavebeenreported.Thepathogen is soil borne and some infection of the tap root is thought to occur in the field priortoharvest.Thefungusisalsoabletosurviveinwoodenstoragebins.Myceliumonthecrownorrootsinitiatesinfectionduringcoldstorage.Myceliumspreadsfromroottorootevenattemperaturesof1°to3°C.Highhumidityandfreemoisturefavordiseasedevelopment. Repeated production of carrot on the same land increases the level of the fungus in soil and makes the disease become worse over time.

Disease Symptoms: Typical symptoms develop after several weeks of lowtemperature storage.Small (5 to10mm indiameter) sunken lesionsorpitsdeveloponthesurfaceofthetaproot.Overtime,therootsdeveloppatchesofwhite,flattenedmycelium.Brownsclerotiamayalsoformonthestoredcarrot.Secondarycolonizationofdamagedareasbysoftrotbacteriaandgraymoldcanleadtosoftrotandentirebreakdown of the roots.

Control


• Croprotation-usearotationthatexcludestheproductionofcarrotsforatleast3to4years,orlonger;

• Sanitation - careful and thorough cleaning and disinfesting of storage andpacking areas;

Figure 7.5 Symptoms of crater rot. Author:Don Edwards

Figure 7.6 Symptoms of carrot fusarium rot. Source: Agricultural Adaptation Council

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• Carrotsshouldbestoredinpolyethylenebags,inconditionsof±0.5°Ctemperatureandrelativeairhumidityof90to95percent.Avoidoverlywetstoragecondition;

• Sanitation-remove and destroy infected plants and tap roots in the field andespeciallyinstorage.

FusariumDryRot

Causal agent – Fusarium spp. Fusariumdryrotisadiseaseofstoredcarrotsorcarrotsheldinthefieldaftermaturity.Thediseasecanoccurwherevercarrotsaregrownandisgenerallyaminordiseaseinmodernstoragefacilities.FusariumdryrotiscausedbyatleastthreespeciesofFusarium.Thesefungiaretypicallysoilborneandcansurviveinthesoilforlongperiodsoftime.Theymayalsobeassociatedwithseeds.Infectionoccursthroughinsectwoundsordamagecausedbyotherfungi.Surfacemoistureandtemperaturesof7°to21°Cpromoteinfection.Undercoolertemperatures,thediseasedevelopsmoreslowly.Thefunguscanspreadfromroottorootbydirectcontact.

Disease Symptoms: Symptoms first appear on the tap root foundation and theentire tap root surface.Typical symptoms are characterized by light-colored sunkenanddryulcers,at thecenterofwhich theepidermiscracksand light-pink tissuecanbeobservedunder it.Ulcersare initiallysmall,and latergradually increase insize. Incasesofsevereinfection,thetaprootdriesandlooksmummified.Light-coloredtissuecanbeobservedonthetaprootwhencut incrosssection.Discoloredtissueismoreconcentrated in the center of the root and looks emaciated on the edges. Boundaries betweendiseasedandhealthytissueareeasytodistinguish.Understorageconditionswhererelativehumidityishigh(95percentandmore),diseasedareasdevelopswhitesoftmyceliaonthesurface.Duringlengthystorage,underconditionsofhighhumidity,whitemyceliachangecolorandturnpinkandyellow.Fusariumdryrotcanalsobecomeawetrot.Insuchcases,diseasedtissueismoist,hasadarkcolorandthereisnosharpboundarybetweendiseasedandhealthytissue.Suchsymptomsappearwhenrelativeairhumidityishigh(95percentandhigher)andtemperaturesarehigherthan10°Cinstorage.Developmentof soft rot isalsoassociatedwith thecolonizationofdiseasedtissues by secondary decay organisms. At the initial stage of disease developmentthe symptomsof Fusariumdry rot strongly resembles thoseofbrown rot.Themaindifference between the two diseases is the optimal temperatures for development of eachdisease–causalagentsofFusariumdryrotdevelopstronglyatthetemperatureof2°C.Brownrotwillnotdevelopordevelopsveryslowlyat2°C.

Control


• Croprotation-usearotationthatexcludestheproductionofcarrotsforatleastthreetofouryears,orlonger;

• Carrot should be produced on light soils capable of good moisture penetration;

• Observetheoptimaldistance(spacing)betweenplantsandrows

• Sanitation - careful and thorough cleaning and disinfesting of storage andpackingareasisnecessary;

Figure 7.8 Symptoms of parsnip yellow fleck virus. Source: DPV-web


Carrot

Figure 7.7 Symptoms of CtRLV. Source: DPV-web

• Accuratelyobserveoptimaltimeperiodsofcropharvesting;

• Disinfectingstoragespacesonetoone-and-a-halfmonthsbeforestoringcarrots,with2percentchlorinatedlime(1kg/100-200m2);

• Storageshouldtakeplaceinconditionsoftemperaturefrom0°to1°Candrelativeairhumidityof90to95percent;

• Sanitation- removeanddestroy infectedplantsandtaproots in thefieldandespeciallyinstorage;

• Because the fungi may be seed borne, fungicide seed treatment may bebeneficial.

CarrotDiseasesCausedbyVirusesCarrotRedLeafVirus(CtRLV)

TheviruscausingthisdiseasedamagesonlyplantsintheUmbelliferaefamily.Thisvirusoftenspreadsincombinationwiththeviruscausingcarrotfleckdisease.Carrotredleafvirusismainlytransmittedbythecarrotaphid(Cavariella aegopodii).Forsystemictransmissionofthevirus,itisnecessaryfortheaphidtofeedonadiseasedplantforaminimum 30 minutes. Several wild plants in the Umbelliferaefamilycanalsobeinfectedbythevirusandserveasasourceofthevirus.

DiseaseSymptoms:Whenyoungcarrotsareinfected,growthisstuntedandthereisareddening,chloroticmottlingandoverallyellowingoftheleaves.Theremaybeatwistingoflowerleaves.Rootsareseverelystuntedandsomeplantsmaydie.Infectionof older carrot plants producesmilder symptoms and infected plantsmay show nosymptomswhentemperaturesareabove24°C.

Control

• Plantspringcropsatleast1.5kmawayfromoverwinteredcrops;

• Controlaphids(insectvectors)thattransmittheviruswiththeuseofaffectiveinsecticides;

• Remove volunteer carrots and weeds from inside and near the planting that can serve as a source of the virus;

• Carrot varieties differ in their susceptibility to the disease.Use tolerant carrotvarieties if available.

ParsnipyellowFleckVirus(PyFV)

Thisvirusistransmittedbycarrotaphid(Cavariella aegopodii) and other aphids. The aphidfeedsoninfectedplantthenmovestoahealthyplantwhereitfeedsanddeliversthe virus in the plant. After completion of an incubation period, the virus is again movedfromtheinfectedplanttoanotherhealthyplantbytheaphid,thusspreadingthe disease.

Disease Symptoms: young leaves on infected plants wilt, while comparativelymature leavesshownosymptomsatthefirststageofthedisease.youngplantsmaycandieveryfastiftheyareinfected.Incaseswhereplantingsareverydense,thedeathof a certain number of young plantsmay go unnoticed. Infection ofmature plants,

Figure 7.10 Symptoms of bacterial leaf blight. Source: The Center for Agriculture, Food and the Enviroment

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producesnecrosisanddeformationofleafstems(petioles)andchlorosisofolderleaves.Inaddition,thetipandsiderootsofthetaprootwilt.

Control

• Controlaphids(insectvectors)thattransmittheviruswiththeuseofeffectiveinsecticides.

CarrotDiseasesCausedbyBacteriaCarrot Soft Rot

Causal agent – Erwinia caratovo.Amongbacterialdiseasesofcarrot,bacterialsoft-rotcanbeespeciallydamaging.Mostvegetablecropscandevelopbacterialsoft rot.Thediseaseisprimarilyaprobleminstorage,butcanalsocausedamageinthefield,especially under conditionswhere the soil stays saturatedwithwater for prolongedperiods.Thebacteriaenterplantsthroughwoundsandnaturalopeningsandrapidlydegrade plant tissues under favorable environmental conditions. High temperature duringstorage(from5°to30°C)andairrelativehumidityof90percentcontributetospread and development of the disease. The disease can also be spread from plant to plant through direct contact.

DiseaseSymptoms:Oncarrottaproots,softrotlesionsaresunkenanddullorange,whiletheepidermissometimesremainsintact.Eventuallyinfectedrootsturnintowet,slimy,rottedmass.Softrotisusuallyaccompaniedbyeveryunpleasantodor.

Control

• Use proper agricultural production techniques that minimize damage to theplantandtaprootandresultsinhealthyvigorousplants.Handleplantscarefullyduring harvest and packing to prevent damage;

• Sanitation-careful and thorough cleaning and disinfesting of storage andpacking areas;

• Maintainoptimalstorageconditions(temperature:1°to2°C,relativeairhumidity:80-85percent).

BacterialLeafBlight(Bacteriosis)

Causalagent–Xanthomonascampestispv.carotae.This common disease occurs in mostcarrotproducingareasworld-wide.Damagingoutbreaksisassociatedwithhighrain fall and overhead irrigation. The bacteria are seed borne and also survive in soil associated with infested carrot debris. The bacteria are dispersed from plant to plant inthefieldinwaterfromsplashingrainoroverheadirrigation.Theseverityofdiseaseisrelatedtotheamountofinfectedseedusedforplanting.Optimumtemperaturesfordiseasedevelopmentare25°to30°C.

Disease Symptoms: The first symptoms are angular yellow leaf spots that laterdevelopintoirregular-shaped,brown,water-soakedspotswithyellowhalosormargins.Theselesionsdryoutandbecomehard.Olderlesionssometimesappearblack.Lesionsdevelopmost commonly at the leafmargins. Formation of a gummy exudates andbrowningofthepetioles(leafstems)alsooccurs.Stemsdevelopoblongwetareasandgrowthofdiseasedplantsmaybestunted.

Figure 7.9 Symptoms of bacterial soft rot. Source: Departments of Agriculture and Food

Figure 7.11 Symptoms of mishapen carrot roots. Source: The Vegetable Crops Research Unit


Carrot

Control

• Useseedthatdoesnothavehighlevelsofthebacteria.Growseedindryregionswithout the use of overhead irrigation;

• Treat infected seeds with hot water;

• Croprotation-usearotationthatexcludestheproductionofcarrotsforatleasttwotothreeyears;

• Copperspraysmaypartiallyreducediseaseseverityifappliedfromanearlystageof plant development.

PhysiologicalDisordersCarrots, like other root vegetables, are subject to several physiological disorders

either in response to environmental or nutritional factors.

• On hot and sunny days, carrot roots may develop bitter flavor due to theaccumulation of a coumarincompoundcalled6-methoxymellein.Thiscompoundalsoaccumulatesinresponsetoinsectorphysicaldamagingoftherootsorwhencarrot roots are storedwith ethyleneproducing fruits like tomatoes, peppers,apples,andmanyothers;

• Rootsplittingoftendevelops fromexposureof theplants to inconsistentsoilmoisture. Carrots are drought sensitive so maintaining the soil moist, but not too wet, will reduce the problem;

• Multiple roots and strong root hairs. Excess nitrogen fromover-fertilizing cancause carrots to form multiple roots or grow strong hairs on the main root. Multiplerootscanalsooccurwhencarrotsaregrownonheavyclayorinrockygrounds;

• Rootswithgreenshoulders.Whenthetops(shoulders)ofcarrotrootsareexposedtolighttheywillturngreen.Hillingthesoilaroundtherootsandincreasingplantpopulation often reduces this problem.

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Pepper

Peppers (Capsicum) aremembersof theSolanaceae family, characterizedby theirdiverseflavorandpungency.Arangeofvarietiesaregrownforbothfreshmarketandprocessing.Theseincludevarietiesthataremildinflavorandthosethathavevaryinglevelsofpungency.Mildflavoredvarietiesincludetraditional“blocky”withthreetofourlopesaswellasvarieties thatare longerwithmorepointy fruitsknownasEuropeanLamuyotypes.Themorepungent/hotvarietiesarenumerousandveryrichincapsaicin.Theactiveingredientisavolatilephenolicfoundonlyintheplacentaorgelsurroundingthe seeds.Thehuman tongue is capableofdetecting10partspermillioncapsaicin.Several varieties of hot peppers are available on the market.

Bellorsweetpepperrespondsverywelltonitrogenfertility.Nitrogenrateofupto400kgperhectareincreasedfruitsizeandyieldbyasmuchas15percentto20percent.For bell pepper, nitrogen application is better when applied in increments starting from bloomuntiltwoweeksbeforeharvest.Hotorpungentpeppersrequire lessnitrogenearly in the growing season and until the fruit reaches fullmaturity. However, highnitrogenapplicationlateintheseasonreducesthepungency.

Bell and hot peppers require constant supply of soil moisture throughout thegrowingseason.Inthecaseofhotpeppers,withholdingwaterafterthefruitreachesmaturityenhancesredcolordevelopmentandincreasescapsaicinsynthesis.

Climaticrequirements

Peppersarewarmseasoncropsthatareverysensitivetofreezingtemperatureatanygrowthstage.Optimaltemperatureforgrowthisabout2o to 3oC higher than that for tomatoes.Pepperplantscantoleratetemperaturesabove38oC,howeversuchextremetemperaturesduringbloomcanreducepollination,fruitset,andyield.Therateofseedgerminationdecreasesrapidlybelow25oCwithgerminationbecomesexceedinglyslowbelow20oC.Daytemperaturesof24o to 30oCandnighttemperaturesbetween9o and 12oCareidealforgrowthandflowering.Pepperdevelopswellinconditionsofincreasedlighting.Optimalsoilmoistureforpepperis70to75percentHB.Thiscropdoeswellondiverse soils from sand to loam soils, rich in organic soils.

Crop Rotation

Peppers, like most other crops require effective crop rotation in order to avoiddisease infection. The best crop rotation system involves legumes, cereals, and acruciferouscroplikecabbageorbroccoli.Itisundesirabletogrowcucumbersinvicinityof peppers, since the former is considered to be a host of the cucumber mosaic virus, whichdamagespepper.Inordertoavoiddamagebycommonpestsanddiseases,itisnotrecommendedtoplantpepperonplotswhichpreviouslyhadothermembersofthesolanaceaefamilylikepotato,eggplant,andtomato,earlierthanafterthreetofouryears.

PEPPERDISEASESPeppershaveseveralimportantdiseasesthatarecausedbyfungi,bacteria,viruses

andphytoplasmas.Themostcommonordamagingdiseasescausedbyfungiinclude:alternariosis(earlyblight),anthracnose,fusariumwilt,greymold,stalkrot,verticilliumwilt,cercosporaleafspot,powderymildewandphytophthorablight.Themostserious

Chapter 8

Figure 8.1 Symptoms early blight in pepper. Source: Plant and Pest Advisory


Pepper

diseasescausedbyvirusesarecucumbermosaicandalfalfamosaic.Stolburisaseriousdisease caused by a phytoplasma. Significant diseases caused by bacteria includebacterial spot, wet rot, bacterial canker and bacterial wilt.

PepperDiseasesCausedbyFungiAlternariosis(EarlyBlight)

Causal agent – Alternarias solani. Thediseaseusuallydevelopsduringthesecondhalf of the growing season. The fungus survives from crop to crop in old plant debris on topof,orburiedin,thesoil.Itcanalsosurviveindamagedorinfectedseedsasmycelium.Underfieldconditions,thefungusspreadsfromdiseasedtohealthyplantsbymeansofconidia.Wateronthesurfaceofplantpartsisrequiredforinfectiontooccur,therefore,the disease is worse on wet conditions.

DiseaseSymptoms:Thediseasedevelopsmainlyonleavesandfruit.Smalldark-greyspotsdeveloponinfectedleaves.Spotsincreaseinsizeandeventuallymergetoformlargenecrotic(dead)areasontheleaf.Leaveseventuallywiltanddie.Thefirstsymptomin fruit is water soaked spots. Spots enlarge to cover large areas on the fruit that become covered with light-colored fungal mycelia. Under conditions of high humidity, thedisease spreadsquickly to create largedamagedareas (lesions)withaquasi-circularshape. With time, damaged fruit become mummified and covered with dark reddish powderysubstance(mycelia).

It shouldbenoted that thepathogencanpenetrateapparentlyhealthy fruitandinfect the seeds. Infected seeds serve as a source of inoculum for the disease. Thediseasecanalsodeveloponfruitinstorageresultinginpost-harvestlosses.

Control

• Sanitation:removeanddestroyalloldinfectedplantdebrisfromthefield;

• Ingreenhouses,thermalorchemicaldisinfectingofsoilisnecessary;

• Balanced fertilization is important for disease control;

• Timely implementation of agro-technical measures, necessary for cropproduction;

• Removebadlydiseasedplantsandfruitfromthefieldduringthegrowingseasonand diseased fruit from storage areas after harvest.

Anthracnose

Causal agent – Colletotrichum capsisi. Anthracnose is considered to be one of the most important and damaging diseases of pepper. The pathogen overwinters inplantdebrisand in infectedseeds.Thediseasespreadsbymeansof fungalsporeswhicharedisseminatedbywind,water,animals,agriculturalequipmentandhumans.Water is required for infectiontooccur.Highrelativehumidity (over90percent)andtemperatures higher than 28°C are favorable for disease development. Anthracnoseusuallydevelopsasthefruitbegintoripeninthefield.Itcanalsodevelopfromlatentinfections in storage and in transport to the market.

DiseaseSymptoms:Circular or angular sunken lesions develop on immature fruit of anysize.Oftenmultiplelesionsappearonindividualfruit.Whenthediseaseissevere,

Figure 8.2 Symptoms for pepper anthracnose. Source: Plant and Pest Advisory

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lesionsmaycoalesce.Oftenpinktoorangemassesoffungalsporesforminconcentricrings on the surface of the lesions. In older lesions, black fungal structures calledacervulimaybeobserved.Withahand lens, these look likesmallblackdots,underamicroscopetheylookliketuftsoftinyblackhairs.Thepathogenformssporesquicklyandcanspreadrapidlythroughoutapeppercrop,resultinginupto100percentyieldloss.Lesionsmayalsoappearonstemsandleavesas irregularlyshapedbrownspotswith dark brown edges.

Control

• Sanitation-Removeanddestroyoldplantdebrisfromthefieldorgreenhouse;

• Use disease free seed;

• Timelyharvestingofthefruitisimportant.Donotletfruitbecomeoverripeinthefield.Fruitshouldbeharvestedindryweather;

• Peppershouldbestoredat3°to4°Cinconditionsofhumidityover90percent.

Fusarium Wilt

Causalagent–Fusariumoxysporum.The pathogen penetrates the plant through the roots. It then colonizes the vascular systemof theplant resulting inwilting andeventuallyplantdeath.

The fungus survives in soil for several years. It is spreadbymeansof agriculturalequipment, infestedplantdebrisandinwater.Highsoiltemperature(33°C)andhighhumiditycontributetodevelopmentofthedisease.

DiseaseSymptoms:ThesymptomsofFusariumwiltcanbeseeneitheronasinglebranch, on several branches on one side of the plant, or on all the lower branches. Initially,Fusariumwiltcausesayellowingandwiltingoflowerleavesoninfectedplants.Theyellowingandwiltingprogressuptheplantasthefungusspreadswithintheplant.yellowed,wiltedleavesoftendryupanddropprematurely.Eventuallytheentireplantwiltsanddiesearly,producingfew,ifany,fruit.PlantsinfectedwithFusariumwiltwillhave a browndiscolorationof the vascular system (the food- andwater-conductingvesselsjustbeneaththeepidermis).Thisdiscolorationcanbeusedfordiagnosis.Cutandpeelbacktheepidermisandcorticaltissueonasectionofthemainstemslightlyabovethesoilline.Iftheareajustbeneaththeepidermishasadistinctbrowndiscoloration,then theplant is infectedwithFusariumwilt.Thediscolorationcanextend from therootsupthestemthroughthebranchesandintothepetioles(leafstalks)oftheplant.

Control

• Sanitation:removeanddestroyinfectedplantdebris;

• Ingreenhouses,thermalorchemicaldisinfectingofthesoilisnecessary;

• Balancedfertilityandtimelyirrigationisimportant;

• Goodagriculturalpracticesforpepperproductionshouldbeused;

• Usediseaseresistantvarietiesiftheyareavailable;

• Thefungussurvivesforverylongperiodsinthesoil.Croprotationforuptofiveorsixyearscanbehelpfulforcontrol.Donotplantsolanaceouscropssuchastomato, eggplant or potato during the rotation period.

Figure 8.3 Symptoms of fusarium wilt in pepper. Source: Diseased pepper and eggplant

Figure 8.4 Symptoms of gray mold. Author:D. Maes


Pepper

GrayMold

Causalagent–Botrytiscinerea.Thepathogenpenetratestheplantprimarilythroughmechanicaldamageanddevelopsunder conditionsofhighhumidity,withinawiderange of temperatures.

Thefungusoverwintersinplantdebris,assclerotia(fungalsurvivalstructures)andmycelium.Thefungushasaverywidehostrangeinfectingalargenumberoffruitandvegetablecrops.Thefungusisoftenspreadmechanically,duringvariousagro-technicalactivities.

DiseaseSymptoms:Thediseasecanaffectleaves,fruitsandstalks.Thefirstsymptomsareusuallywater-soakedspotsonthefruit.Asarule,thefruitskinremainsundamaged,butwrinkles. Diseased areas of the fruit soften and are sunken. In time the surfaceofdiseased tissuebecomes reddish andgrayish in color. Eventually the fruit surfacebecomescompletelycoveredwithmyceliaandgreysporesofthefungus.Thisiswherethediseasegets itsname(graymold)Leavescanalsodevelopgraywetspots,whicheventuallybecomecoveredwiththegrayfungalgrowth.

Control

• Maintainoptimaltemperaturesandsystematicventilationingreenhouses;

• Observeoptimalplantingdensity;

• Remove lower tier diseased leaves;

• Timely applications of effective fungicides are important for controlling thedisease.

Stem and Fruit Rot

Causalagent–Didymellalycopersici,Phomadestructiva,Phomaexiqua. The disease requireswatertodevelopandismostsevereunderconditionsofhighhumidity.Fungalspores are transportedbywind and splashing rain.Thepathogen invades theplantthroughmechanicaldamageandthroughnaturalopeningsintheplant.Initialinfectionsources are soil, plant remains and seeds.

DiseaseSymptoms:Thediseasedevelopsontheplant’smainstalk.Darkgray-greenspotscanbeobservedonthebottompartofthestem.Eventually,thebottompartofthestemiscompletelycoveredbythespots. In laterstagesofdiseasedevelopment,necrosis develops in the plant’s vascular system, and small red dots (fungal fruitingbodies)canbeobservedonthesurfaceofdiseasedtissues.

Control

• Sanitation-Removeanddestroyinfectedplantdebris;

• Incaseofgreenhouses,thermalorchemicaltreatmentofsoilandmaintainingoptimaltemperatureandhumidityarenecessary;

• Use disease free seed for planting.

Verticillium Wilt

Causalagent–Verticilliumdahliae,Verticilliumalbo-atrum.The pathogens survive forlongperiodsoftimeinthesoil.Theycanretainvitalityforatleast15years.Infection

Figure 8.5 Symptoms of fruit rot and steam lesions. Source: Michigan State University

Figure 8.6 Symptoms of pepper verticilium wilt. Source: Ontario Crop IPM

Figure 8.7 Symptoms of cercospora leaf spot. Author: Matthew Orwat

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occurs from direct penetration of mycelia or throughmechanical damage receivedduring transplanting or cultivation. Verticillium wilt is most serious during mono crop production,especiallyonlight-sandysoils.Hightemperature(25°C)andlowmoisturecontentinthesoilprovideoptimalconditionsfordiseasedevelopment.Consequently,diseasedevelopmentintensifiesinJulyandAugustanddecreasesinastemperaturescool during September and October. This process affects the plant and during thisperiodcertainrestorationtakesplaceandnewgrowthmaydeveloponthelowerpartof the plant.

DiseaseSymptoms:Thefirstsymptomsofthediseaseareobservedbeforebloom.Infectedplantsarecharacterizedbyweakgrowth,andsmalldarkgreenleaves.

Lower leaves wilt and develop spots, which gradually spread to the whole leaf.Damagedleavesturnyellow,developnecrosisanddropfromtheplant.Eventually,theplantwiltscompletelyanddies.Plantsinfectedatearlystagesofdevelopmentfailtodevelop knots, while plants infected during later stages of development have small and shrunkenfruit.Rootsofdiseasedplants lookhealthyatfirstsight,but laterdarken.Abrowndiscolorationinthevascularsystemcanbeobservedifstemsarecutvertically.

Control

• Croprotationmustbedoneforlongperiodsoftimeandmaynotbepracticalforcontrollingthedisease.IfsoilsareheavilyinfestedwithVerticillium,peppersandother solanaceous crops should not be planted;

• Soil fumigation is effective for controlling the disease, however, the fungus can rapidlydecolonizefumigatedsoil;


• Ifavailableusediseaseresistantvarietiesandhybrids.

Cercospora Leaf Spot

Causal agent – Cercospora capsici. The fungus survives in infested plant debris in the soil,atadepthofupto10cm.Ifinfestedmaterialisplaceddeeperthan10cmbelowthe soil surface, the fungusquickly loses vitality. In thefield, thedisease spreadsbymeans of fungal conidia. The disease is general most severe near the end of the growing seasonolderandphysiologicallyweakplants.Highhumidityanddewprovidefavorableclimatic conditions for disease development.

DiseaseSymptoms:At first, lower leaves of the plant develop multiple spots, which have whitish centers and dark red ring around them. When the disease is severe, lower leavesmay yellow anddry completely anddie,while upper leaves remain relativelyhealthyinappearance.

Control

• Timelyapplicationofeffective fungicides ishighlyeffective forcontrollingthedisease;

• Sanitation - Remove and destroy infected plant debris from the field orgreenhouse;

• Deepplowingtoburyplantdebrisbelow10cm.

Figure 8.9 Symptoms of phytopthora blight in pepper. Source: Feeding Knowledge Organsiation


Pepper

PepperPowderyMildew

Causalagent–Erysipheoronti.Powderymildewcanbeaseriousdiseaseofpeppersinwarm,arid,andsemiaridgrowingregions.Infectionoftenleadstodefoliation,whichcanleadtoseverelossesoffruit.Thefunguscaninfectmanyhostsforoverwinteringand long-term survival. Powderymildewcanoccur inbothdry andhumid climates.Unlikemostother fungalpathogens, freewateron theplant surface isnot requiredfor infection.Conidiaofthefunguscangerminateatanyrelativehumiditywhenthetemperatureisbetween10°and35°C.Thepathogenisspreadbywindblownconidia.Onceinfectionhasoccurred,warmdays(above30°C)withhumid,coolnights(below25°C) favor rapiddiseasedevelopment.The incidenceofpowderymildew inpepperisgreatest inhumidclimates,butdefoliationof infectedplants ismoresevere indryclimates.

DiseaseSymptoms:The most noticeable of the sign of the disease is a white powder growthontheundersideofleaves.Lightgreentoyellowlesionswithnecroticcentersmay form on the upper leaf surface. Eventually, the entire leaf turns pale yellow orbrownish.Symptomsdeveloponolderleavesfirst.Whenconditionsarehighlyfavorablefordiseasedevelopment,thepathogenmaysporulateontheupperleafsurface.Theedges of infected leaves eventually curl upward, revealing the fungus on the lowersurface.Infectedleavesdropprematurelyfromtheplant,exposingfruittothesun,sothattheymaysubjecttosunscald.

Control

• Timely applications of effective fungicides are important for controlling thisdisease;


• Isolatingthegreenhouseplantingsfromfieldplantingsofpepper;

• Disinfectgreenhousesoilandstructures.

PhytopthoraBlight

Causalagent–Phytophthoracapsici.ThefungusthatcausesPhytophthorablightsurvivesasthick-walled,resistantspores(oospores)inthesoilandasmyceliumininfectedplantissues.Onceintroduced,thesefungicansurviveupto15monthsinmoistsoilintheabsenceofhostplants.Theycanalsobecarriedonseedortransplants.Thefungusrequiresfreewaterinthesoilforinfectiontooccur.Becauseofthis,initialinfectionsusuallyoccuronplantsgrowinginpoorlydrainedareasoffields.Oncesteminfectionoccursthefungiproducesporeson infectedstemtissues,whicharethencarriedbysplashedrainontonearbyplants.Lowerbranchesofadjacentplantscanalsobeinfectedbyrain-splashedsoil contaminatedby run-offwater. Fruits in contactwith the soil areespeciallypronetoinfection.Sporesareproducedonnewlyinfectedfruitandstems,andnewinfectionscandevelopquickly.Warmwetweatherismostfavorablefordiseasedevelopmentandspread.Diseaseprogressdeclinesunderdryweatherconditions.

DiseaseSymptoms:Thediseaseaffectsbothseedlingsandmatureplants.Infectedseedlingsshowtypicaldamping-offsymptoms.Infectionofolderplantsusuallybeginsatorbelowthesoil line.Water-soaked,darkbrownlesionsonthelowerstemusuallyextendupwardabove the soil lineandmayexpand togirdle the stems,preventingupward movement of water and nutrients. This often results in a sudden wilting of

Figure 8.8 Symptoms of powdery mildew on pepper leaves. Source: Feeding Knowledge Organisation

Figure 8.10 Symptoms of stolbur in pepper. Source: Phytoplasmas and pyroplasmas

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foliage.Rootinfectionsmayalsooccurwhichkillrootsandcauseswiltingoftheplantwithout the appearanceof stem cankers.The foliar phaseof this disease commonlyoccurs at forks in the branches, resulting in dark, girdling canker sand wilting of leaves andfruits.Infectedleavesdevelopcircularorirregular,darkgreen,water-soakedlesionswhichdryandappear light.Fruit lesionsmayalsoappearasenlarging,watersoakedareas,whichthenshrivelanddarken.Amassofwhitefungalgrowthmaydevelopinsidethefruit,andseedsusuallyturndarkbrownorblack.Afine,grayish-whitetotanmoldmayalsobecomeevidentoverthelesiononthefruitsurface.Underhumidconditions,fungalgrowthdevelopsextensivelyovertheentirefruit.

Control

• Useonlycertifieddisease-freeseedortransplants;

• Avoid depressions on the surface of the beds where water can accumulate, especially around the base of plants. Avoid planting peppers or cucurbits inpoorlydrainedfields;

• Usecroprotationso thatpeppersaregrownonlyevery three to fouryears toreducetheamountofPhytophthorainthesoil.Usenon-susceptiblecropssuchas corn, small grains beans, crucifers, or potatoes in the rotation.

• Applicationsoffungicidesmayreducediseasedevelopmentandspreadifusedin combination with cultural practices such as crop rotation and raised beds.

PepperDiseasesCausedbyVirusesandPhytoplasmasStolbur

Causalagents–Phytoplasma.Stolburiscausedbyaphytoplasma,whichessentiallyisabacteriumwithoutacellwall.ThediseaseusuallyappearsduringperiodsofhighsoiltemperatureandcanaffectseveralplantsinthefamilySolanaceae such as pepper, tomato,eggplantandpotato.Thepathogenistransmittedbyinsects. InGeorgia,thedragonflyHyalestes mlacosewichi is considered to be the most important insect vectors.

Spreadof thisdiseasesignificantlydependsuponthe rateof reproductionof thepests which transmit or vector the disease. Larvae of the insect vector overwinter on rootsofvariousplants,ofwhichweedhostsareespeciallyimportant.

Stolbur is characterizedwith sharplymanifested cyclical pattern – after epiphyteends,spreadingofthediseasesignificantlyweaken.

Disease Symptoms: Infected plants are stunted and develop chlorosis or intenseyellowcoloroftheleaves.Symptomsareobservedmostclearlyonupperleaves,whichyellowandtear.Atthistime,theupperleafsurfacehasayellowcolor,whilethelowerleafsurfaceisviolet.Diseasedleavesareinitiallyhardandbreakable,duetoaccumulationofstarch in them. Flowers become sterile. Fruits that are set before the disease develops donotdevelopnormally.Theyarethin-walledandtasteless.Eventually,plantsbegintowiltanddie.Wiltingoftheplantisaresultofrottingoftherootsystem.Rotbeginsfromtheroottips.Infectedrootsaredarkincolorandeasilyseparatedfromtheroot.

Control

•It is recommended toplantpepper early in thegrowing season,before theinsectswhichtransmitthediseasebeginflying,whichoccursinthebeginningormiddleofJune;

Figure 8.12 Symptoms of AMV in pepper. Source: Cornell University


Pepper

• Inter planting corn or sunflower togetherwith pepper aids in controlling thediseasebecause it confuses theflyingpatternof the insects that transmit thedisease;

• Timelyapplicationsofinsecticidestocontroltheinsectvectorarerecommended.Preference should be given to systemic insecticides with prolonged effectcapability.

CucumberMosaicVirus(CMV)

Causal agent – Cucumber mosaic virus. Thisvirusspreadsrapidlyunder favorableclimatic conditions.

Itoverwintersininfectedplantdebrisandistransmittedbyaphidsandismechanicallytransmittedbyagriculturalmachineryandequipment.

Disease Symptoms: Symptoms of the disease can be highly variable, dependingupon the variety of pepper and the timeof infection.Diseased leavesmaybecomenarrow and deformed and develop shot holes. When mature plants are infected, leaves falldownandleafdiscolorationcanbeobserved.Thetopoftheplantmayalsodryup.

Asarule,diseasedplantsgrowweaklyandhavedeformedfruit,onwhichconcentriccircles are sometimes noticeable.

Heaviest economic damage is caused when plants are infected at an early age.Severelyinfectedplantsproducefruitsthatareuselessforconsumptionandmarketing.

The number of the CMV virus host plants is quite large and includes up to 800different plants.

Control

• Controltheinsectvectors(Aphids)thattransmitthedisease;

• Removeanddestroyinfectedplantsandplantdebrisfromtheplanting.

AlfalfaMosaicVirus(AMV)

Causal agent – Alfalfa mosaic virus. Alfalfamosaicvirushasaverywidehostrangeinfectingmanybroad leafplants.Asa rule, thisdiseasespreadstopepperwhen it isgrownnearfieldsplantedwithalfalfa.Thevirusistransmittedandrapidlyspreadsbymanytypesofaphids.Italsospreadsbymeansofagriculturalequipmentandseeds.

DiseaseSymptoms:Alfalfamosaicischaracterizedwithsharp-yellowmosaic.Fruitsare often dotted and deformed.

Control:

• Growpepperawayfromalfalfafields;

• Useeffectiveinsecticidestocontroltheinsectvectors(Aphids).

PepperDiseasesCausedbyBacteriaBacterial Leaf Spot

Causalagent–Xanthomonascampestrispv.Vesicatoria.Bacterial spot of pepper is one of the most destructive diseases of pepper in climates where high temperature and

Figure 8.11 Symptoms of CMV on leaves. Picture Source: Crocus

Figure 8.14 Symptoms of bacterial canker on leaves. Source: Ohio State University

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frequentrainfalloccurduringthegrowingseason.Thediseasecausesspotsonleavesandfruit,leafdefoliation,andreductioninplantgrowth,fruityield,andquality.Bacterialspot is also a serious problem on tomato, although no tall strains of the pathogen can causediseaseonbothhosts.Thebacteriacanoverwinterincropresidue(debris)inoron soil, on or in seeds, and on wild host plants. Pepper seeds infested with the pathogen are a major source of inoculums for the disease as well as the major means of long distance spread of the pathogen. The pathogen can survive on dried seeds for up to 10years. It isnotabletosurvive free insoil fora longtime,butcansurviveuptosixmonths in infected crop debris in soil. The bacterium penetrates leaves through stomata (naturalopeningsintheplant)andwounds.Bacteriaoftenenterfruitsthroughwoundscreatedbywind-drivensand,insectpunctures,ormechanicalinjury.Disseminationofthebacteriaoccursbetweenandwithinfieldsbywatersplashing,aerosols,orduringcultivating, hoeing, thinning of direct seeded plants, transplanting, or harvesting.

Disease Symptoms: On sweet pepper, disease symptoms appear on the leaves,stalksandfruit.Incaseofhotpepper,symptomsarecomparativelylessexpressed.Firstsymptomsmanifestasirregularlyshaped,water-soakedspots,appearingonthebottomsides of the leaves. Under wet conditions the spots appear water soaked. These spots latergrow insizeandbecomedarkbrownorblack incolor.During thisperiod, spotcentersareyellowish-brown,whiletheirmarginsaresemi-transparentyellow.Diseasedareasontopsidesoftheleavesare,asarule,slightlysunken,whileonthebottomoftheleaves, theyprotrude.Leaves severelydamagedby infectionoftendevelopchlorosisanddryup.Severely infectedplantsmayalsodefoliateprematurelyordevelop shotholes and have a ragged appearance.

Onstemsandpetioles,lesionsareelongatedandblackened,andcankillleaflets.

On fruit, spots initially develop as water-soaked areas, which later turn necrotic.Spotshaveapimplysurface,whichburstswithtime,astheirsizeincreases.Itshouldbenoted,thatunderwet,humidweatherconditions,secondaryfruitrotoftendevelopsonthedamagecausedbybacterialspot.

Control

• Sprayingwithfungicidecontainingcoppermayaidincontrollingthedisease;

• Control weeds in and near the planting, especially weeds in the familySolanacacae;

• Removeanddestroyinfectedplantsandplantdebrisfromtheplantingarea;

• Usehigh-qualitydisease-freeseedandtransplants;

• Refrain from walking or conducting agricultural practices in the planting when the plant leaves are wet from dew, rain or irrigation;

• Practice crop rotationwith non-host plants such as corn, so that peppers aregrownonlyeverythreetofouryears;

• Cleaning (disinfesting) agricultural equipment andmachinerybefore enteringnew land areas aids in reducing the spread of disease and its introduction into new areas.

Bacterial Canker

Causal agent – Clavibacter michiganensis. Bacteria representing the Clavibacter family aremost often spread through the use of infected seeds or transplants. The

Figure 8.13 Symptoms of bacterialleaf spot. Source: Plant Pest Advisory

Figure 8.15 Symptoms of bacterial wilt on pepper stem. Source: Hawaii Plant Diseases


Pepper

disease requires water to infect plants and develop. Therefore, the disease is mostsevere under conditions of high relatively humidity, rain or overhead irrigation.Daytemperaturesof25° to30°Care ideal fordiseasedevelopment.Denseplantings thatpreventgoodaircirculationandincreasedryingtimeofplanttissuesalsocontributetodiseasedevelopment.Movementofagriculturalequipment,humanactivitiesintheplanting, and insect pests are also factors which contribute to spreading the disease. Thebacteriapenetratetheplantmostlythroughmechanicaldamageorotherwounds.

Disease Symptoms:Disease symptomson theplant are representedby spots onthe foliage and fruit. At times the plants can become systemically infected, but thisis relatively rare.During local infection, initial symptomsappear as small bubblesorprotrudingwhite spots on leaves and stems.Gradually, the center of the spots turnbrownandasemi-transparentmargindevelopsaroundthem.Stemsdevelopareasofstiffenedtissue,whichgrow involumeandform large lesions.Diseasesymptomsonfruitappearassmall,round,slightlybulgingspots.Thesespotslatergrowinsize,theircenters turn brown andwhite, and they develop a semi-transparentmargin or haloaround them. When spot numbers and size increases, plant tissue develops stiffened areas.Ifplantsbecomesystemicallyinfectedtheyusuallydie.

Control

• Sprayingwithfungicidecontainingcoppermayaidincontrollingthedisease;

• Control weeds in and near the planting, especially weeds in the familySolanacacae;


• Usehigh-qualitydisease-freeseedandtransplants;

• Refrain from walking or conducting agricultural practices in the planting when the plant leaves are wet from dew, rain or irrigation;

• Practice crop rotationwith non-host plants such as corn so that peppers aregrownonlyeverythreetofouryears;

• Cleaning (disinfesting) agricultural equipment andmachinerybefore enteringnew land areas aids in reducing the spread of disease and its introduction into new areas.

Bacterial Wilt

Causal agent – Ralstonia solanacearum. Bacteria of the Ralstoniafamilyspreadfromthesoilandarecapableofretainingvitalityinthesoilandplantremainsforlongperiodsoftime.Bacteriapenetratetherootthroughdamage,whichmaybecausedtotherootby nematodes, during seedling transplanting, soil cultivation and other agriculturalpractices.Manyweedsmayharborthebacteriaintheirrootsyetshownosymptoms.High temperatures (eg.30° to35°C)andhighsoilmoisture favordevelopment.Highsoil moisture increases the survival of the bacteria in soil, the rate of infection, the rate of disease development after infection, and the number of bacterial cells released from thehostintothesoil.Bacterialwiltisagreaterprobleminheavysoilsandinlowlyinareas that can retain soil moisture for long periods.

Disease Symptoms: The disease occurs in scattered plants or groups of plants in the field. Wilting begins with the youngest leaves during warm or hot weatherconditionsduring theday.Theplantsmay recover temporarily in theeveningunder

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coolertemperatures.Afewdayslatersudden,permanentwiltoccurs.Thewiltedleavesmaintain their green color and do not falls the disease develops.

Therootsandlowerpartofthestemhaveabrowningofthewater-conductingtissues(vascularsystem)oftheplant.Infectedrootsmayrotduetosecondaryinfectionsfromotherpathogens.Diseasedrootsorstemsthatarecutandplacedinasmallcontainerofwaterwillshowasteady,yellowishorgraybacterialoozecomingfromthecontend.

Control

• MaintainthesoilpHwithinthelimitsof5.5to5.7;

• Plantpepperonlyonsiteswithgoodsoildrainage.Avoidpoorlydrained,wetsites;

• Practice crop rotationwith non-host plants such as corn, so that peppers aregrownonlyeveryfourtofiveyears;


• Useonlyhigh-qualitydiseasefreetransplants;

• Controlweedsinorneartheplanting,especiallyweedsinthefamilySolanaceae.

PhysiologicalDisordersPeppers, like tomato and several other crops, are susceptible to a variety of

physiologicaldisorders.Blossomendrot,fruitcracking,andsunburn/sunscaldcanbeproblems under certain conditions.

Blossomendrot(BER)isaseriousprobleminpeppers.Similartotomatoandmelons,blossomendrotaffectsonlythedistalendofthefruitstartingatearlystagesofdevelopment.BERismoreseriousinbellorsweetpeppersthaninhotpeppersbecauseofthetendencyoffarmers to use heavier doses of nitrogen on bell than hot peppers. Also, the larger size fruits of bell pepper are more prone to BER than the smaller fruits of the hot varieties.

Control

• Applysimilarrecommendationfortomato;

• Use calcium nitrate instead of other formulations of nitrogen;

• Use resistant varieties or varieties that tend to have smaller fruit sizes.

Sunburn/Sunscald

High temperature, clear skies, and intensive light radiation can cause severe sunburn inpepperfruits,especiallybellorsweetvarieties.Therearethreetypesofsunburn.Thefirstisknownassunburnnecrosis,whichisinducedbyexposureofthefruittointensiveand direct sunlight. Fruit skin and peel of affected areas of the fruit turn brown and die. Sweetpeppersdevelopthistypeofsunburnwhenthefruittemperaturereaches40o to 42oC. Hot peppers develop sunburn but at a much lower percentage.

Thesecondtypeofsunburniscalledsunburnbrowning.Inthistypeofsunburn,theexposedfruittissuesturnlightbrownbuttheydonotdie.Thistypeofsunburnoccursat5oto6oCcoolertemperaturesthansunburnnecrosisorbetween35oto37oC.Intensivelight radiation also contributes to this disorder.


Pepper

Thethirdtypeiscalledphoto-oxidationsunburn.Thissunburndevelopsinshadedfruitsthataresuddenlyexposedtodirectsunlighteitherthroughpruningorthroughshoot breakage.

Control

• Fruitsunburniscontrolledbydevelopingadequateleafcanopytokeepthefruitsfromdirectexposuretothesun,especiallyintheafternoon;

• Diseases thatdefoliate the leaves andwiltingdue tomoisture stress can alsoexaggeratetheproblem.Sokeepingplantshealthyreducesthedisorder;

• Somevarieties, especially those that are tenderor havedarker fruit color, aremore susceptible to sunscald;

• Excessivepruningordamagetothecanopycanincreasetheincidents.

Fruit Cracking and Scarring

Fruit cracking is not as serious a commercial problem in pepper as it is in tomato, exceptwhensomevarietiesaregrownunderhightunnelsoringreenhouses.Howeverfruit scarring, sometimes called rusting, especially in hot pepper varieties, can be aserious problem.

Control

• Fruitscarringisgeneticallycontrolledandsoselectingaresistantvarietiesisthebeststrategytoreducethedisorder;

• Keepsoilconsistentlymoist.Fluctuationofsoilmoisturecancausecrackinginsome varieties.

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Beet (Beta vulgaris var. crassa) belongs to the family Chenopodiaceae, commonlyknown as goosefoot family. This family also includes sugar beet, Swiss chard, andthe commonweed lambs quarter (chenopiodium album). The following informationcoversonlytableorfreshmarketbeets. Inmanypartsoftheworld,thebulkoftablebeet is grown as an annual crop for its edible roots. However, a small percentage of the orientalis group, known as Spinach beet, is grown for its leaves. At least three different coloursofbeetrootsareavailablecommercially;red,white,andyellow.Beetisacoolseason crop that tolerates occasional frost and mild freeze. The optimum temperature forseedgerminationisatabout5oC.Fullydevelopedplantsprefertemperatureintherangeof10o to18oC,withexposuretohigher temperatureresulting in fastergrowthandformationofwhiteringsintheroot,knownas“zoning.”Beetplantsgrownforseedproduction require a coldperiodof about twoweeksat 4o to10oC to induceflowerstocksformation(bolting).

Soil,waterandpHrequirements

Beet plants prefer deep andwell drained sandy or silt loamwith higher organicmatter content. However, plants can also grow on heavier soils, but root growth will be restrictedandharvestmaybedifficulttomanage.Beetplantshaverelativelylargerootsthatcanextendseveralfeetinthesoil,thereforeitishighlydesirabletogrowtheplantsin soils rich in organic matter.

Maintaining uniform soil moisture and following an appropriate crop rotation is importantinreducingthepotentialofseriousroot-rotdiseaseslikedamping-off.Beetrootsaresensitivetodamping-offwhengrowninpoorlyaeratedsoilorinsitesthattendtoflood.Beetissensitivetoacidsoils;thereforetheidealsoilpHshouldbemaintainedbetween 6 and 7.5. Application of acidifying fertilizers, like ammonium sulphate, tosoilswithhighbufferingcapacitymayresult in reducingthesoilpHtobelow6.Thissituationusuallycorrectsitselfafterthefertilizerfinishesreactingwiththesoil.However,continuousapplicationofacidicfertilizertosoilswithhighbufferingcapacitymayleadto reducing itsbufferingcapacityandso reducingtheuseofacidic fertilizersand/orlimeapplicationmaybeneededtocorrecttheproblem.LimeisusuallyneededinacidicsoilsthathavelowpHsAnapplicationof2.5to8tonsoflimeperhectare,dependingonthesoilbufferingcapacity,isusuallyneededtoraisethepHtoabove6.

Fertilizers Management

Underidealsituations,fertilizertypesandratesshouldbebasedonsoilandtissueanalysis.

Nitrogen. Nitrogenapplicationratesdependonthesoiltypeandcropsgrownbeforethebeet.Generally,anapplicationrateof170to240kgperhectareisrecommendedforgoodleafgrowth.Thelowerrateisusuallyrecommendedwhenbeetisgrownaftera legumecropwhilethehigherrate isappliedafteranon-legumecrop.Theamountofnitrogenisusuallysplitintotwoapplications,oneincorporatedintothesoilbeforeplanting and the other side dressed about two weeks after planting.

Phosphorus. Phosphorusisimportantforestablishmentofhealthyplantsthatcantoleratedamping-off.Anapplicationof60to80Kgperhectareofsuperphosphateortriplephosphateincorporatedat2to3cmbelowtheseeddepthisrecommendedforbeet. However, combinations of phosphorus and nitrogen and potassium and boron

table beet


table beet

should be broadcasted and not incorporated under the seed in order to avoid burning theyoungseedlings.

Sulphur. Sulphuricanothermacroelementneededbytheplantsinordertosurvive.Sulphur is marketed in two formulations, as sulphate and as elemental sulphur. Plants arecapableofabsorbingonlythesulphateform,butnottheelementalform.Elementalsulphur has to be converted by the soil bacteria to the sulphate form so the plantcan use it. The conversion is faster in finer soil under moist and warm conditions. The recommendedsulphaterateis18to22kg/hectareappliedtothesoilatplantingtime.Finelygroundelementalsulphurshouldbeappliedtheyearbeforeplantingat35to45kg/hectare.

Boron. Boron is themost importantmicronutrient required by beet roots. Plantsrequire3to6kg/hectareofboronasapre-planttreatment,aswellas,additionaltwoto threespraysofwater solubleboron (1kg/hectare) inorder topreventcollapseofyoung leaf tissue and development of root canker. Root canker is characterized byhollow and black crown, due to water accumulation. Rough black spots can appear on theroots,whichgivestherootsabittertaste.Therootsmayeventuallybecomeentirelydiscoloured,hollowed,and/orsplit.Theyieldandqualityofcultivatedbeetrootscanthereforebeseverelyaffected.Borondeficiencycanalsoresultincorkygrowthontheshootsandstalks.Rootsfromborondeficientplantsstorepoorly.

BEETDISEASESTablebeet and sweetbeetshave the samediseases. Importantdiseasesofbeets

inGeorgiathatarecausedbyfungiinclude:BlackLeg(Phomarootrotandleafspot);CercosporaLeafSpot,DownyMildew,Rust,GrayMoldandPowderyMildew.Importantdiseases that are causedby viruses include: BeetMosaic andBeetCurlyTop (BCTV).Amongbacterialdiseasesofbeets,themostcommondiseasesareCrownGallandRootTuberculosis.

BeetDiseaseCausedbyFungiBlackLeg(PhomaRootRotandLeafSpot)

CausalAgent–Pleosporabjoeringii(Phomabetae).Black leg is an important disease of beets and can result in serious crop losses under environmental conditions favourable for disease development. Black leg is causedby the fungusPleospora bjoeringii. The asexual stageof the fungus isPhoma beta .Thepathogen is usually encountered inthefieldondiseasedplantsastheasexualstage(Phoma betae). Phoma produces small blackgloboselypycnidia(fungalfruitingstructures)onthesurfaceofinfectedtissues,andthesepycnidiaareusefulindiagnosingthedisease.Phoma betae is a seed borne pathogenandiscommonlyintroducedintotheplantingininfectedseeds.Theoptimumconditionsfordiseasedevelopmentaretemperaturesof14oto18oC and long periods of high relative humidity.Water on the surface of the plant is required for infectiontooccur.Thepathogen is spreadbetween seedlingsby fungus spores (conidia) thataresplashedbyrainor irrigation.Later in theseason, thesexualstageof the fungus(Pleospora bjoerinii) develops andproduces another type of fungal fruiting structure(pseudothecia).These structures can survive andoverwinter in crop residues in andontopofthesoil.Inthespring,thepseudothecia can produce air borne spores which causeleafspotsinnewlyplantedcropsandsteminfectionsinseedcrops.Atharvest,if

Figure 9.1 Symptoms of black leg in beet. Source: New York's Food and Life Sciences Bulletin

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beet leaves are trimmed to the root or if roots are wounded, the fungus can enter the rootandcausearootrotinstorage.Postharvestrootrotisfavouredbytemperaturesabove15oC,butcanoccuratmuchlowertemperatures.Ifrainoccursclosetoseedcropharvest time, seed borne infection can increase.

DiseaseSymptoms:Symptomsonyoungplants includepre-emergencedampingoff,where seedandgerminated seedlingsdiebeforegrowingaboveground.youngseedlings that emerge can develop black lesions (spots) on stem tissues that are incontact with soil. These lower stem infections can turn the entire stem black and rotted. Thisiswherethediseasegetsthename“blackleg.”

Symptoms on leaves are pale brown leaf spots that canmeasure up to 2 cm indiameterandcontainconcentricringsofthefungalfruitingbodies(pycnidia)ofPhoma betae.Thesespotsaremostlyfoundonolderleaves.

Inseedcrops,infectedstemsdevelopdarkstreaksandlesions(diseasedareas)withgraycentres.Severeinfectioncausesstemstobreakatthecrownandrootstohaveadryblackrot.

Infectedrootsinitiallyhavewater-soakedlesions(diseasedareas)whichturnbrownand develop into deep, sunken black lesions containing gray white mycelium andpycnidia. Severely infected roots become spongy and full of cavities. Root rot oftendevelops during storage of table beets.

Control

• Alwaysstart theplantingwithpathogenfreeseeds. If infectedseed isused, itshould be treated with an effective fungicide seed treatment. Seed can also be treatedusinghotwater soaks.Water iswarmedtoa temperatureof50°Candseedsaresoakedat this temperature for20minutes.Seedsare thenremovedfromthewaterandchilledincoldwaterandallowedtodry;

• Croprotation-Ifthisdiseaseoccurs,beetsshouldberotatedwithnon-susceptiblecropsforatleastthreetofouryears;

• Correctapplicationoffertilizers,inparticular,timelyapplicationofboron;

• Sanitation-Removeanddestroyinfectedplantsandplantpartsfromthefield.Deepploughingtoburycropresiduesafterharvestisbeneficial;

• Store beets properly to prevent root rot in storage. Beets should be kept insmallboxeswithacapacityof15-20kg.Storagefacilitiesshouldbethoroughlydisinfested with chlorine (40 grams per litre of water). After disinfection, thestoragefacilityshouldbeventilatedforatleast24hours;

• Maintain proper storage conditions. The optimal temperature for beet storage is 0oto20Cwitharelativehumidityof90to95percent;

• The timelyapplicationofeffective fungicidescanbebeneficial for controllingcertain diseases.

Cercospora Leaf Spot

Causal agent – Cercospora beticola. Cercospora is one of the most widespread and damagingbeetdiseasesinGeorgia.ItaffectsnotonlyTableBeet,butalsoalfalfa,peas,bindweeds,amaranthandmanyothercultivatedorwildplants.Croplossescanexceed40percentonarootweightbasisand,underconditionshighlyfavourablefordisease

Figure 9.2 Symptoms of cercospora leaf spot of beets. Source: The Centre for Agriculture, Food and the Environment at the University of Massachusetts


table beet

development, almost complete crop loss can occur. The fungus over winters as sclerotia ininfectedleaves,thesesclerotiacanremainviableinsoilforuptotwoyears.Thefungusalso overwinters in infested crop residues in and on top of the soil, infected seeds, and on infected wild weed hosts.

Sporesofthepathogenarespreadbyslashingwaterandwind.Sporegerminationand infectionoccursmost rapidlyat25oto35oC when night temperatures are above 16oCandrelativehumidityisabove90percent.Diseaseactivityisreducedbelow15oC. Spotsappearatsevento10daysafterinfection.

DiseaseSymptoms:Circular leaf spotsareatfirst small (up to2mm indiameter),andcanbeverynumerous,coveringalmosttheentire leaf.Spotshaveapalebrownoroffwhitecentrewithareddishmargin.Later,spotsexpandinsize, remaincircularoroblong,andcanresultinseverelossoffoliage(defoliation).Thecentresofthespotseventuallybecomegrayandmayfalloutcausingashot-holeeffect.Usually,infectionand leafdropbeginsonthe lower leavesthenmovesuptheplanttoaffectyoungerleaves.

Control

• Use disease resistant varieties if available;

• Sanitation - remove and destroy infected crop debris and destroy volunteerplants;

• Donotplantvegetableproductioncropsclosetoseedcrops;

• Use seed thatdonothavehigh levelsof infection. If infected seedsareused,applyaneffectivefungicideseedtreatment;

• Ensure appropriate plant spacing and distance between rows to promote better aircirculationintheplantingtoreducedryingtimeofplanttissues;

• Timelyapplicationsofeffective fungicidescanprovideeffectivecontrolof thedisease.

DownyMildew

Causal agent – Peronospora farinosa. f. sp. betae. The oomycete pathogen canoverwinterasmyceliainseeds,oninfectedweedhosts,andonvolunteerbeetplants.The pathogen produces thick walled resting spores called oospores that can survive for long periods in the soil, alone or inside infested plant residues. The pathogen is seed borne so it can spread in seed. About one percent of infected seeds result in infected plants. Overwinteringmycelia produce structures called sporangia that are airborneandarespreadbywind.Optimumconditions fordiseasedevelopment iscool,moistweather(optimumtemperatureis8oC).Thepathogenrequiresatleastsixhoursofleafwetnessandcooltemperatures(optimum7oto15oC)infecting.Littleinfectionoccursabove20oC.

DiseaseSymptoms:Downymildewcaninfectplantsatallstagesofdevelopment.First symptoms are yellowing and distortion of the youngest leaves. The pathogengrowssystemicallywithintheyoungleavesandmayinvadethegrowingpoint,resultinginreducedgrowthandspindly,deformed,yellowleaveswhichcurldownwards.Underhumid conditions, a densepurple-gray growthofmycelium appears onboth upperandlowerleafsurfacesofinfectedleaves.Individualspotscanalsodeveloponleaves.

Figure 9.3 Symptoms of downy mildew. Author: Melodie Putnam

Figure 9.5 Symptoms of beet root gray mold. Source: The AgroAtlas

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Thesespotsareyellowandareirregularinshape.Latertheydryupandturnbrown.Ifthegrowingpointhasbeeninvaded,adarkheartrotofthecrownmayoccur.Ifolderplantsareinfected,sometimestheycanrecoverandproduceadditionalleavesthatarehealthy.

Control

• Use seeds that do not have a significant level of the pathogen. Obtain anduse seedsproduced indry regions that arenot favourable fordownymildewdevelopment;

• Removevolunteerbeetandweedplantsthatcancarrythedisease;

• Sanitation-removeanddestroyinfectedplantsandplantresiduesfromthefield;

• Thetimelyapplicationofeffectivefungicidescanbeeffectiveforcontrol.

Black Leg Beet Rust

Causalagent–Uromycesbetae.The fungus attacks plants during the vegetation period. Thepathogenhasacomplex lifecycleandproduces severaldifferent typesof spores.The pathogen overwinters in seed crops, volunteer beet plants and susceptible weeds. Thefungusmayalsobeseedborne.Urediniosporesaretheprimarysporesresponsiblefor spreading the disease. These spores are windborne and the optimum temperatures fortheirgerminationare inarangefrom10to22oC.Anothertypeofspore(teliospore)is important as an overwintering structure that can survive on crop residues and for up tooneyearonthesoilsurface.Rustdevelopmentiffavouredbywarm(15oto22oC)andmoistconditions.Thediseaseisinhibitedbydryconditionsandhighertemperatures.

DiseaseSymptoms:Themainsymptomsareatypicalorangerustpustulethatisraisedandis1to3mmindiameter.Pustulesdeveloponboththetopandbottomoftheleaf.Necrotic tissuedevelopsaroundthe largerpustules,especiallywhenpustulesdevelopin clustersor rings.When thedisease is severe, leavesmaybe completely coveredbypustules,andbecomecoveredwiththepowderyorangesporesthatareproducedwithinthepustules.Severelyinfectedleaveseventuallyturnyellowanddie.Whenthediseaseissevere,itcancauseprematuredeathofleavesandresultinreducedyieldandquality.

Control

• Sanitation-removeanddestroyinfectedplantresiduesfromthefield;

• Search for and remove diseased volunteer beet plants and susceptible weed hosts from the area;

• Crop rotation;

• Insure appropriate spacing between the plants and crop rows to improve aircirculation in the planting;

• Thetimelyapplicationofeffectivefungicidescanprovideeffectivecontrol.

GrayMold

Causalagent–Botrytiscinerea.Thedisease isprimarilyaprobleminstorage.Thefungus infectsbeet roots in storageprimarily thoughmechanical injury (wounds)ortissuesdamagedbycoldinjury,insects,orotherdiseases.Thefungusisspreadbyair

Figure 9.4 Symptoms of beet rust. Source: Rheinische Friedrich-Wilhelms-Universität Bonn


table beet

borne spores from infected to healthy roots and is also spread by direct contact ofdiseasedtohealthyroots.Themajorcauseofthisdiseaseispoorstorageconditions.

DiseaseSymptoms: First signs of the disease appear during harvest. Roots develop brownspots.Thetissueunderthesespotsmaybecomeyellow.Theyellowingappearsonlyunderconditionsofhighhumidity.Infectedtissuesdevelopgrayflakesandblackfungalsclerotia.Instorage,infectedrootsbecomewatersoakedandrot.Theybecomecoveredwithadenselayerofgrayfungalmyceliumandspores.Thisiswhythediseaseiscalled“graymold.”

Control

• Store beets properly to prevent root rot in storage. Beets should be kept insmallboxeswithacapacityof15-20kg.Storagefacilitiesshouldbethoroughlydisinfestedwithchlorine(40gr.perlitreofwater).Afterdisinfection,thestoragefacilityshouldbeventilatedforatleast24hours;

• Maintain proper storage conditions. The optimal temperature for beet storage is 0o to20Cwitharelativehumidityof90to95percent;

• Useproperagriculturalproductiontechniquethatminimizedamagetotheplantandresultsinhealthyvigorousplants.

PowderyMildew

Causalagent–Erysiphebetae.Powderymildewisadryweatherdisease.Wet,rainyconditions will slow disease development. Powdery mildew spores have high watercontent(60percent)andcangerminateatlowrelativehumidityintheabsenceoffreewater. Spore germination occurs over a wide range of environmental conditions, with anoptimumof25oCand70 to100% relativehumidity. Epidemicsareassociatedwithdryweather alternatingwith periods of high relative humidity. Spores can germinateandpenetrate into theplantwithina fewhours.The fungus soonproducesa layerofpowderywhitemyceliumandconidiagrowthonthesurfaceofinfectedplantparts.Thispowderywhitegrowthiswherethediseasegetsitsname“powderymildew.”Thefungusoverwinters in buried roots and on volunteer beet plants and susceptible weed hosts. Thefungusalsoproducessexualfruitingstructurescalledcliestothecia.Thesestructurescanoverwinterincropdebrisandreleaseanothertypeofspore(ascospore)inthespringthatcancausenewinfections.Severeattacksofthediseasecanreduceyieldbuyupto25percentandtablebeetcropswithbadlydiseasedleavesmaybeunmarketable.

DiseaseSymptoms:Thefirstsignsofpowderymildewarescattered,smallcoloniesofthefungusconsistingofsuperficialwhitefungalgrowth.Thisgrowthusuallystartsonolder leaves and occurs on both upper and lower leaf surfaces. As the disease develops, theentireleafcanbecomeheavilycoveredwithextensivepatchesofthewhitepowderyfungal growth. Older leaves with severe powderymildewwill turn yellow andmayeventuallydie.Ifthediseaseisverysevere,youngerleavescanalsobeinfected.

Control

• Timely applications of effective fungicides are important for controlling thisdiseaseonhighlysusceptiblevarieties;

• Sanitation - remove and destroy infected plant residues from the field. Afterharvest,ploughdownanddestroycropresidues;

• Search for and remove volunteer beet plants and susceptible weed hosts.

Figure 9.6 Symptoms of beet powdery mildew. Author: Howard F. Schwartz

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BeetDiseaseCausedbyViruses

BeetMosaicVirus(BtMV)

Causal agent – Beet Mosaic Virus. Virus diseases are of major economic importance onbeets.Beetmosaicvirusiscommonworldwide.Thediseaseusuallyappearsfirstinseedproductionplotsduringearlyspring,onthefirstleavesproducedfromtheroot.The appearance of the disease in seed plots is due to the fact that the roots used for plantingbecame infectedwiththevirusduringthefirstyear.Therefore,mosaicvirusinfectedrootswereusedforplanting.Thevirusisspread(vectored)byseveralspeciesofaphidsincludingthepeachaphid.Thevirushasaverywidehostrangethatincludesmanyspeciesofcropplantsinseveraldifferentplantfamilies.Severalweedspeciesarealso important hosts.

Disease Symptoms: Disease symptoms on infected plants are not always visible.Symptoms are oftenmasked (not visible) if temperatures are highor too low. If thetemperatureismorethan210Candlessthan100C,diseasesymptomswillnotappearonnewlyformedleaves.Oncesymptomsappearonleaves,theywillnotbedisappearingunder adverse temperatures.Themost common symptom is a pale green to yellowgreenmottleormosaicpatternon the leaf.Thismosaic symptom is similar toothermosaicdiseasesymptoms.Theyoungertheleaf,themoreeasilynoticeableisthemosaicmottling.As leavesmature, disease symptomsgradually subsideonnew leaves andeventuallyvanish.Thismosaicpatterncanbeseenonannualplantsandseedplants.The latterdevelopdiseasesymptomsaftercuttingof sprouts,duringgrowthofnewleaves.Inadditiontomottling,theleafbladeoftenundergoesdeformation.Thisdiseasecanalsocauseanintensivegrowthofvegetationand,rarely,tissuenecrosis,wherepartoftheleafbladediesandhasdryspotsappearingonit.

Abackwardcurlingoftheleaftipmayoccur.Thisisacharacteristicsymptomofthedisease, but does not always occur on infected leaves. Infected plantsmay becomestunted.

Control

• Alwaysusediseasefree(virusfree)seedsandplantingmaterial;

• Search for and remove wild species of susceptible weeds and volunteer beet plants near the planting;

• Control the aphid vectors that introduce and spread the virus.

BeetCurlyTopVirus (BCTV)

Causalagent–Beetcurlytopvirus.The virus is an important pathogen on table beets. Itcaninfectmanyothercropplantandseveralcommonweedspecies.Inadditiontobeets, this disease also affects pepper, tomato, spinach, legumes, cucurbits, and plants inthesolanaceae,caryophyllaceaeandumbellíferaefamilies.Thevirusisvectoredbyleafhoppers. In theMediterranean region, the leafhopper,circulifero pacipennis, has been reported to be a vector.

Disease Symptoms: The most common symptoms are reduced growth (stuntedplants)andreducedleaves.Leafveinsappearthickenedandlosecolourandbecometransparent.Ifthediseaseissevere,theveinswilldevelopnecroticbrownlinesofvariouslengthsalongtheirsides.Theselineswilllaterexudeglue-likefluid.Leavesareseverely

Figure 9.7 Symptoms of beet mosaic virus. Authors: C. M. Rush and G. B. Heide

Figure 9.8 Symptoms of BCTV. Author: Howard F. Schwartz


table beet

rolled upwards, crinkle, and sometimes form swollen growths that are visible on the lowerleafsurface. Infectedleavesmayalsobecomethickandpowdery.Leafpetiolesmaybeshortenedandbendinwards.Therootcanbedistortedandhaveaproliferationoffineroots,resultingina“hairyroot”symptom.Thevirusisrestrictedtothephloemofthe plant and phloem tissue can be necrotic when seen in dissected roots.

Control

• Alwaysusediseasefree(virusfree)seedsandplantingmaterial;

• Search for and remove wild species of susceptible weeds and volunteer beet plants near the planting;

• Control the leaf hopper vectors that introduce and spread the virus.

BeetDiseaseCausedbyBacteriaCrownGall

Causal agent – Agrobacterium tumefaciens. This disease most often occurs in sugar beets,thoughitcanalsoaffecttablebeets.Causalagentattacksmanyculturalandwildplants.

DiseaseSymptoms: Underground parts of beets develop protuberances of various sizes.Theycanbethesizeofakidneybeanor largerthantherootsthemselves.Thisdiseasemainlyappearsintheareaoftherootneckandmorerarelyinthelowerpartsofroots.Thesurfaceofthegallsismostlyuneven,knobbyorwrinkled,andcoveredwithprotective tissue.Atfirst thegallsare softandwhite. In time theybecomehardandusuallyturnbrown.Asarule,itdoesnotrot.Tissueunderprotuberancesiswhite.Therearenobacteria inoldergalls.Bacteriacanonlybe found inyounggallsduringearlystages of the disease development.

Control

• Adhere toagro-technical rulesand timingofbeetproduction,harvestingandstorage;

• Usedisease-freeseedmaterials;

• Removeanddestroyinfectedplantsandrootsfromthefieldandstorageareas.

Tuberculosis of Beet

Causalagent–Xanthomonasbeticola.Causal agent is stored in the soil, from where it penetrates roots through mechanical injuries.

Disease Symptoms: Symptoms are very similar to those of crown gall but differfrom itby the sizeofprotuberances,whicharenot large in thecaseof tuberculosis.Protuberances are dark-coloured, knobby growths that are attached to the roots byawidebase.Unlike crowngall, theseprotuberances haveholes. Bacteria are alwaysconcentratedindamagedtissues.Rotmaydevelopinthecentresoftheknobbygrowthsduring the vegetation period.

Rootsinfectedwithtuberculosisarenotsuitableforstorage.Tissuesintheknobbygrowthsroteasilyandareofteninvadedbysecondaryorganismsthatrottheroots.

Figure 9.9 Symptoms of crown gall. Source: KWS UK - Product Portfolio

Figure 9.10 Symptoms of tuberculosis of beet. Source: agroatlas

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Control

• Adhere toagro-technical rulesand timingofbeetproduction,harvestingandstorage;

• Usedisease-freeseedmaterials;

• Removeanddestroyinfectedplantsandrootsfromthefarmandstorageareas.

Harvesting and handlingHarvestoftablebeetbeginsabout45-65daysfromseedsowing.Harvestingshould

bedoneatthecoolestpartoftheday,usuallyearly inthemorning.Rootsshouldbethoroughly washed and cooled as soon as possible. The optimum temperature forstorageisbetween1oand4oC. To prevent or reduce root cracking, avoid wetting and dryingoftherootsafterharvest.

PhysiologicalDisordersRootzoningischaracterizedbyalternatingredandwhiteringsintheroottissue.The

disorderisassociatedwithhotweatherandwhenbothdayandnighttemperaturesarewarmorhot.Incontrast,thedisorderdoesnotdevelopasreadilyunderwarmdaysandcooler nights.

Remedy

Themost effective strategy to reduce root zoning is to plant resistant varieties.Anotherpractice to reduce rootzoning is to reducesoilmoisturebyusing reflectivemulches, keeping the soil damp, and planting cooler sites.

Figure 9.11 Root zoning. Source: Gardening Cornell University


onion, Garlic

Onion(alliumcepa)andgarlic(alliumsativum)belongtothefamilyaliaceae,whichalso includes chive, shallot and leak. Onions and garlic are among themostwidelyadaptable vegetables in theworld.They can be grown successfully from tropical tosubarctic regions.

TemperatureandDayLengthRequirements

Onion and garlic are cool to moderate season vegetables. Plants require cooler(about20°C) temperaturesduring theearly stagesofgrowthandmoderatelyhighertemperatures (28°C) for best bulbdevelopment andmaturation.yellow varieties areusuallyplantedearlierthanredvarieties,becausetheycantoleratehighertemperatures.

Theygrowbestwhen theday time temperature iscoolandnight temperature isrelativelywarm.However,thewideadaptationofonionandgarlicisprimarilyduetotheirresponsetodaylength.Unlikemanyothervegetables,daylengthinfluencesbulbformationratherthanflowerdevelopment.

Onionbulbsareclassifiedintothreegroupsbasedontheirresponsetoday-length.

1. Short-dayvarieties.Thesevarietiesformbulbwhenday-lengthisbetween11-12hours;

2. Intermediate day-length varieties. Includes varieties that form bulbs at day-lengths of 13-14 hours.These varieties are adaptable to the central regionofGeorgia;

3. Long-dayvarieties.Thesevarietiesstarttoformbulbatday-lengthsof16hoursor more.

SoilRequirement.

Many types of soils are suitable for growing onions andgarlic, but the ideal soilshouldbe loose(friable)andwell-drained.Soggyandheavysoilsbecomefirmwhentheyaredry,makingthemdifficultforthebulbstogrow.Idealsoilsshouldalsobefertileandhighinorganicmatter.Onionandgarlicplants,however,donotperformwellwhenover fertilized.

TheoptimumsoilpHforplantgrowthisintherangeof6.0to6.5.Applicationsofdolomitelimeorcalcitelimeishighlyrecommended,ifsoilpHisbelowortheabovetherecommendedrange.Dolomitelimeispreferredifsoilmagnesiumlevelislow,whilecalcitelimeisrecommendedifsoilmagnesiumishigh.IspHisadequate,butthesoiltest indicateslowcalciumthenusegypsuminstead.SoilpHcantakeseveralmonthsto change with lime applications. If soil testing indicates low pH, lime or gypsumtreatmentsshouldbedoneasearlyaspossible toensure thatsoilpH iscorrected insufficienttimeforplanting.

VarietiesOnion

Inadditiontoclassificationofonionvarietiesbasedonday-length, therearealsoclassificationbasedonbulb color, country of origin, and shapeof thebulb. Storageonions,alsocalledfallandwinteronions,havethreemaincolors-red,white,oryellow.

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Varieties named after their country or city of origin include Bermuda onion, amildflavored onion, Egyptian onion, a strong flavored onionwith edible leaves, Spanishonion,amilderflavoronionthathasred,whiteandyellowbulbs,Wallaonion,alargesweetonion,andVidaliaonion,alsoasweetandverytenderonionfromtheStateofGeorgia in theUSA.There are also scallionsor springonion, shallots, amilderflavoronion that resembles garlic, and several others.

Garlic

Garlicvarietiesareclassifiedintohardneck(alliumsativumvar.ophioscorodon)andsoftneck(A.sativumvar.sativum).Softneckvarietiesareadaptabletoawiderrangeofclimates,theykeeplongerinstorage,tendtomaturefaster,andtheyaregenerallymore productive than hard neck varieties. Most of the hard neck varieties do best where winteriscold,springisdampandcool,andsummerisdryandwarm.Theclovesofhardneckvarietiesarefewerperbulb,relatively larger insize,andeasiertopeelthansoftneck varieties. Hard neck varieties also demand more attention than soft neck varieties toproducegood-qualitylargebulbs.Buttheyaremorecolorfulandoffervarietiesofflavor.Hardneckvarietiesproduceanedibleflowerstalk,prizedforitsdelicateflavorwhen harvested while it is still tender. Removing the stalk encourages more bulb production.

Production Practices

Onionandgarlic require relatively similarproductionpractices. Short-dayonionscanbegrownfrombothseedandtransplants,but themajorityofonionsaregrownfrom transplants. However almost all commercially grown garlic is producedmostlyfrom cloves but a few growers prefer using transplants.

Transplant production begins in late summerwith land preparation followed byseed sowing in September. Land for transplant production should not have been in onionsorrelatedAlliumsforatleastthreeyears.

Ahectareofonionandgarlic requiresaboutakilogramofseeds.Anareaof300-500mseedbedproducesenoughtransplantsforonehectare.Seedsareusuallysowninrowssetonbeds7-10cmapart.Seedsaredistributedthinlyandevenlytopreventdampingoff.Plantsarehardenedbyreducingwateringandexposingtheseedlingstofull sunlight for about seven to ten hours prior to transplanting in the field.

At four to five weeks after sowing, transplants are hardened for about 10 daysby placing them in a partially shaded area and watering them less frequently butmaintaining sufficientmoisture to preventwilting. Hardened transplants aremovedintothefieldandplantedatadistanceof15cmbetweenrowsand3-5cmbetweentransplants in the row.

Irrigation

Transplantsshouldbewateredwithabout2.5cmsoonafterplanting inthefield.Dependingonsoiltypes,irrigationvariesbetweenfourandsevendaysuntilabouttwotothreeweeksbeforeharvestorwhen20-30percentofthetopsstarttofoldover.Thelast irrigation should be a light one.


onion, Garlic

Nutrient Management

Asmentionedearlier,onionandgarlicplantsrequiresufficientnutrientsinordertoproduceaneconomicallyviablecrop.Thebeststrategytonutrientmanagementistobasefertilizerapplicationonsoilandplantanalysis.Asageneralrule,fullydevelopedonionandgarlicplantsrequireabout130to150kg/hectareofactualnitrogen,usuallyappliedinthreeequalincrementsstartingtwoweeksaftertransplantingandcontinuingduringtheearlystagesofbulbformation.

Lowlevelofpotassiumcausesplantstobecomemoresusceptibletocoldinjury,whilelowlevelofphosphorousreducestheabilityofcarryitsbiologicalfunctions.Assumingthatsoilanalysisindicatedlowtomoderatelevelsofpotassiumandphosphorous,therecommended rate to apply is about 100 to about 130 kg/hectare of each of theseelements.Heavyrainfallorirrigationcausessoilappliedpotassiumtoleachingreadily.Therefore,itisrecommendedtosplitpotassiumapplicationbyincorporatinghalfoftherecommended rate before planting and splitting the remaining half into one to two side dressing applications.

Sulfur is very important for onion and garlic plant growth and bulb quality.Therecommendedsulfurrateisbetween45to50kg/hectaresplitintotwoequalapplications,one before planting and the other side dressed before plants start to form bulbs. Boron isrequiredbyonionandgarlicplants.Ifsoilboronislow,asinglesoilapplicationof1.2kg per hectare needs to be incorporated prior to transplanting of seeding. Higher rates ofboroncancauseinjurytogrowingplants.

Weed Control

Onionandgarlicareweakcompetitorswithotherplantsandsotheydonotthrivewellinweedyareas.Thereareonlyalimitednumberofherbicidescurrentlyregisteredforuseongarlicandonion.Forbestgrowthstartwithaweed-freeareaandmulchwithclean straw after planting.

ONIONANDGARLICDISEASESOnionsandgarlichaveseveraldiseasesthatcanbeveryseriousunderenvironmental

conditionsthatareconducivetodiseasedevelopment.Diseasesofonionandgarlicarecausedby fungi, viruses andbacteria.Mostonionandgarlicdiseases are causedbyfungi.Themaindiseasesthatarecausedbyfungi include:DownyMildew,LeekRust,Neck Rot of Garlic, Alternaria Blight, Neck Rot ofOnion,Onion Smut, FusariumWilt,WhiteRotofOnion,andBlackMoldRotofOnionBulbs.

Themostimportantdiseasecausedbyavirusisonionmosaicvirus,andthemostimportantdiseasecausedbyabacteriumisbacterialsoftrot.

OnionandGarlicDiseasesCausedbyFungiDownyMildew(Peronosporosis)

Causal agent – Peronospora destructor. Downymildewiscausedbytheoomycetepathogen, Peronospora destructor. It is a very destructive disease of onion and cangreatly reduceyieldandqualityof foliageandbulbs.Thedisease ismostsevereandepidemics develop best under prolonged periods of cool, wet weather. Infection

Figure 10.1 Symptoms of downey mildew in onion. Source: Plantesygdomme

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requirescooltemperatures(lessthan22°C)andthepresenceoffreewater.Theoptimumtemperatureforgerminationofsporangia(spores)is10°to12°C.Sporescangerminateandpenetratetheleafthroughnaturalopenings(stomata)intwotofourhours.Sporesareproducedatnightandare releasedandcarriedbywindcurrentsduring thedaytohealthyleaveswheretheyinfectandspreadthedisease.Sporescansurviveontheleafsurfaceforuptothreedays.Periodsofwarmeranddryweathercanstopdiseasedevelopment.Theoomycetepathogenisanobligateparasiteandproducesthickwalledsurvival structures called oospores that can survive alone in the soil or in infected bulbs. Myceliumofthepathogencanalsosurvivewithininfectedbulbs.Coldwintersappeartoreducetheincidenceofthediseaseduringthefollowingyear.Thepathogencanalsobe seed borne.

Disease Symptoms:Thedisease ismanifestedboth asdiffusive (widespread) andlocal damage. Plants that emerge from damaged bulbs develop widespread damage. Initially,theplantdevelopsnormally.Aftertwotofourweeks,leavesbecomeyellowish,andarecoveredbyawaxlikepowderygrowthofthepathogen.Diseasedleavesbecomedeformed.Duringseveredamage,leavesbecomesoftenedandmaycollapse.Inhumidweather they are covered with dark gray-violet powdery growth of the pathogen,whichconsistsofspores(sporangia)ofthepathogen.Thesesporesaretransferredtohealthyplantsonwindcurrentswhere they infect the leaves in thepresenceof freewater resulting in new infections and further spread of the disease. At this time, leaves develop oval yellow spots of various sizes, which grow quickly and their surface iscoveredwithadarkgray-violetpowderygrowthofthepathogen.Thepowderygrowthgraduallyspreadstothewholesurfaceoftheleaf,whichisfollowedbywilting.Indryerweather, damaged areas appearmainly aswhite (chlorotic) spots. At times, infectedleavesmaynotbecoveredwiththepowderygrowth,butdamagedleaveseventuallydie in this case as well.

Frominfectedabove-groundorgansthepathogenpenetratesintotheonionbulbs,where itdevelopsmostly in the toppartof thebulb. It is impossible todifferentiatedamagedonionbulbsfromhealthyonesthroughvisualinspection.However,damagedbulbs do not survive well in storage. Most infected bulbs will develop mold and rot easily.Bulbsdamagedinstoragearenotmarketable.

Withtime,thecolorofthedarkgray-violetpowderygrowth,existingondamagedorgans, changes and turns to dirty gray. Also, many saprophytic fungi (Alternaria,Cladosporium,Stemphyliumandothers)causesecondaryinfectionsondiseasedleavesandstalksandbegintoreproducethroughtheformationofspores.Asymptomofthisprocess is blackening of diseased plant parts. Seed material taken from such plants is of verypoorqualityandwillgiverisetodiseasedplantsinthefield.

Control

• Usediseasefreeplantingmaterial.Heattreatmentmayreducetheviabilityofthepathogen in infected planting material. Proper heat treatment of seed material is conductedbyplacingseedmaterialat the temperatureof43° to45°C foraperiodof20-24hoursoratthetemperatureof35°to37°Cforaperiodoffivetosevendaysandnights;


• Careful and thorough cleaning and disinfesting of storage areas must be performed;


onion, Garlic

• Croprotation-Usearotationthatexcludestheproductionofonionsforatleastthreetofouryears;

• Sanitation-Usesanitarymeasuressuchastheuseofcleanseedbedsawayfromtheproductionofcrops.Removeanddestroyinfectedplantpartsinthefieldandin storage;

• Controlweeds,especiallyvolunteeronionplantsinandneartheplanting;

• Applications of an effecting fungicide can be important for controlling this disease.Weeklyapplicationsmayberequiredstartingbeforesignificantdiseasedevelop.

Leek Rust

Causal agent – Puccinia allii. Leek rust is causedby theobligateparasitic fungus,Puccinia allii.The rust fungusdoesnot survive in soil.Orangeurediniosporesare theprimaryinoculumforthedisease.Thesesporescanbecarriedoverlongdistancesbywinds. The source of the primary inoculum for somemajor epidemics in California,U.S.A.,wasneveridentified.Optimumconditionsforinfectionare15°Cand100percentrelative humidity for four hours. Rust infections can be favored by high nitrogenapplications and low potash levels.

DiseaseSymptoms:Thefirstsymptomsconsistofsmall(1to2mmindiameter)leafflecksandspotsthatareirregularinshapeandwhiteorlighttanincolor.Thesespotsincreaseinsizeto3to5mmthendevelopintobrightorangepustules(warts)thatarefull oforangedusty spores.These“rustpustules” are typical symptomsofmany rustdiseasesonotherplants.Rustusuallyappearsonolder leavesfirstand later spreadsto younger leaves. Severely infected leaves can be almost completely coveredwithpustules.Severeinfectioncanresultindeathofleaves,reducedplantsizeandyield.

Control

• Usediseasefreeplantingmaterial.Heattreatmentmayreducetheviabilityofthepathogen in infected planting material. Proper heat treatment of seed material is conductedbyplacingseedmaterialat the temperatureof43° to45°C foraperiodof20-24hoursoratthetemperatureof35°to37°Cforaperiodoffivetosevendaysandnights;

• Use proper agricultural production techniques that minimize damage to theplantandresultsinhealthyvigorousplants.Avoidoverorexcessivefertilizationwithnitrogenandmaintainsufficientlevelsofpotash;

• Croprotation-Usearotationthatexcludestheproductionofonionsforatleasttwoyears;

• Applications of an effecting fungicide can be important for controlling this disease.

NeckRotofGarlic

Causal agent – Sclerotinia porri. Thepathogenoverwintersasmyceliumindiseasedbulbs,asmyceliumininfectedbulbsinstorage,andinplantdebrisinthefield.Itcanalsooverwinterinsoilassclerotiawhicharetinyblacksurvivalstructuresproducedbythe fungus in infected tissues.

Figure 10.2 Symptoms of leek rust. Source: Naga negi

Figure 10.3 Symptoms of neck rot of garlic. Source: Plant Diseases Management Handbook, Midwest

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Environmental conditions that favor disease development and spread are high levels ofsoilmoistureandrelativehumiditycombinedwithcooltemperatures(13°to15°C).

Disease Symptoms: During storage, garlic cloves develop small, slightly sunken,yellowish or dark spots that are several millimeters in diameter. These spots laterincrease in size, the cloves wilt and eventually dry down and mummify. Underconditionsofhighmoisture,diseasedtissueiscoveredwithagraypowderygrowthofthefungus.Ifdiseasedclovesareusedforplanting,theemergingplantsareweakandchlorotic(yellow).Whenmatureleavesofautumngarlicareinfected,theyrotandplantseventually die. Internal layers of infected bulbs darken and develop black sclerotiawhich are visible within infected tissues.

Control

• Sanitation-Removeanddestroyinfectedplantpartsinthefieldandinstorage;

• Croprotation-Ifthediseaseoccurs,usearotationthatexcludestheproductionofgarlicforatleastfouryears;

• Usediseasefreeplantingmaterial.Ifplantingmaterialisinfected,useaneffectiveseedtreatmentfungicide(Bayleton,Fundazol);

• Maintain proper storage conditions. Storage facilities should be thoroughlycleanedanddisinfested.Drybulbsbeforeplacementinstorage.

Alternaria Blight

Causal agent – Alternaria alli. The pathogen overwinters in infected seed material, diseasedonionbulbs,andplantremainsinthefield.Duringthevegetationperiod,thefungusspreadsfrominfectedtohealthyleavesbymeansofconidiathatareproducedbythefungusoninfectedtissues.Conidiaarespreadbywindorinsplashingwater.Thediseasecandevelopoverawiderangeoftemperaturesfrom2°to35°C.Thepathogenpenetratestheplantprimarilythroughmechanicaldamage.Freewaterfromrain,dewor overhead irrigation is required for conidia germination and for theproductionofconidiaoninfectedtissues.Thediseaseismostsevereonphysiologicallyweakplants,aswellasolderplants.Excessivenitrogenfertilizationalsoresultsinincreaseddamagefrom the disease.

DiseaseSymptoms:Thediseasefirstappearsononion leavesor its veins, initiallyaslightspots.Thespotsquicklygrowandtheirlengthoftenreaches10cmandmore.Finally,spotssurroundthediseasedareas.Colorofthespotschangesconstantlyandfinallyassumesabrownish-violetcolor.Spotsoftenhavewhitemarginorhalo.Damagedtissueseventuallydryandbreak. Later thediseasemoveson toonionbulbs.At thistime,diseasedtissueisinitiallycolorlessandthenassumesareddish-darkgraycoloring.Greenish-darkgraymoldappearsbetweenthelayersofthebulb.Diseasedareasoftendevelopasecondaryblackmold.

Control


• Croprotation-Ifthediseaseoccurs,usearotationthatexcludestheproductionofgarlicforatleasttwoyears;

• Use proper agricultural production techniques that minimize damage to theplantandresultsinhealthyvigorousplants.Avoidoverorexcessivefertilizationwith nitrogen;

Figure 10.4 Symptoms of alternaria blight in leaves. Source: Information for Commercial Vegetable Production in Ontario


onion, Garlic

• Applications of an effecting fungicide can be important for controlling this disease.

NeckRotofOnion

Causalagent–Botrytisallii.Neckrotismainlyastoragedisease.Underpoorstorageconditions,thediseasecanresultinlossesgreaterthan50percent.Producersthatdonothave facilities fordryingonionsprior to storagemayhavesignificant losses.Thepathogenistransmittedonseedandplantingmaterial.Ifseedisstoredatsufficientlylow temperatures the fungus can survive on seed for more than three years. Thepathogen produces conidia on infected seeds that spread the disease to new leaves to causeinfections.Duringthegrowingseason,infectionmayberestrictedtotheleaves.Justpriortoharvest,thebulbonionfoliageistoppedorbentcreatingwoundsonthebulb that are open to infection. While neck tissue retains moisture, the pathogen grows into the bulb where it causes rot. Tiny black sclerotia, which are survival structuresproducedbythefungus,areproducedwithininfectedtissues.Sclerotiacansurviveforatleasttwoyearsinburieddebrisinthefield.

DiseaseSymptoms:Inthefield,plantsdevelopwhitespots,withthelengthof1-5mmandalightgreenmarginorhalo.Thesespotsmayresembleherbicideinjury.Theycanbedifferentiated fromone another only bymeans of the light greenmargin orhalothatdevelopsaroundthespotscausedbyneckrot.Althoughbulbinfectionmayoccurinthefield,mostofthedamagecausedbythediseaseoccursinstorage.Typicalsymptoms instorageareawater-soakedor lightbrownrotattheneckofthestoredonionbulb.Adensegraygrowthofmyceliumisproducedaroundtheneckandbetweenthebulbscales(layers).Manytinyblacksclerotia(5mmindiameter)alsodevelopontheneckofthebulb.Themyceliumgrowthusuallybecomesapparentafterseveralweeksinstorage.Thepathogencontinuestospreadthroughthebulbandeventuallymostofthebulb becomes a soft, rotted mass.

Thetissueoncutsofdiseasedbulbsdiffersradicallyfromhealthytissue:itisblackand softened.

Insomecases,diseasedbulbsdevelopdryrot.Theymummify,andbecomecoveredwithapowderyfungusgrowthandblacksclerotia.Diseasedbulbsareofteninvadedbysecondarybacteriaandfungithatresultinvarioustypesofrot.

Control

• Croprotation-Ifthediseaseoccurs,usearotationthatexcludestheproductionofgarlicforatleasttwotothreeyears;

• Timelyharvestingofthecropisimportant;

• Avoid mechanical damage to the bulbs;

• Observeoptimalstorageregimes:Temperaturesshouldnotexceed30°to32°Candrelativehumidityshouldbemaintainedbelow80percentaslongaspossible;

• Rational use of mineral fertilizers: Fertilizers containing nitrogen should be added during the crop growth period, while phosphorus fertilizers should be used duringthesecondhalfofvegetation.Itisundesirabletousefertilizerscontainingnitrogen eight to nine weeks after planting;

• Timelyandhigh-qualityproperchemicaltreatment.

Figure 10.5 Symptoms of neck rot in onion. Source: WikiGardener

Figure 10.7 Symtoms of fusarium wilt on onion. Source:WikiGardener

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Onion Smut

Causalagent–Urocystiscepulae.The fungus is soil borne and can survive for up to 20yearsinsoil.Sporesproducedbythepathogen(chlamydospores)arespreadbywindandsplashingwater.Theoptimumtemperatureforsporegermination is13°to22°C.Mostplantinfectionsoccurat10°to12°C.Diseasedevelopmentandspreadisgreatlyreducedat temperaturesabove25°C. Infectionandsymptomdevelopmentaremostserious in production fields where onions are produced from seeds. Plants are far more sensitive to the disease during the period from seedling emergence until formation of thefirstleaf.Afterreachingtheheightof8-10cm,onionsrarelybecomediseasedwithsmut.

Disease Symptoms: Symptoms can appear as early as seedling emergence,whencotyledons showsymptoms.The cotyledonsandfirst leavesdevelopoblongto elongated, dark, raised blisters on outer surfaces. These growths can cause a downwardcurlingoftheleaves.Whenmature,thedarkblistersbreakopentoexposeablack,powderygrowthof the fungus.There isprogressivespreadsof thediseaseinwardwhich can kill seedlings in three to fourweeks. Infectedbulbs remainfirm;however, secondarydecayorganisms canpenetratedamagedareas and cause thebulb to rot.

Control

• Use fungicide treated seeds;

• Usehealthytransplantsbecausetheyareabletoresistinfectionfromsoilborneinoculums;

• Plant when soil temperatures are higher;

• Sanitation-removeanddestroyinfectedplantdebris.

Fusarium Wilt and Bulb Rot

Causal agen – Fusariumozysporum,FusariummoniliformeandFursariumculmorum.The disease is common and can result in severe loses of both onion and garlic. The pathogensaresoilborne.Theysurvive insoilasresistantspores(clamydospores).Thepathogensarecarriedononionsetsandgarliccloves.The fungimayalsobeseed borne. The optimum temperature for disease development is 25° to 28°C,and the disease is seldom a problemwhen soil temperatures are less than 15°C.Thesefungicanpenetratetherootsandspreadtothebaseofthebulb.Theycanalsopenetrate thebulbdirectly.Damagefrom insect feedingorothercausescanincrease the disease. Wet weather close to harvest favors disease development, especiallyingarlic.

DiseaseSymptoms:Symptomson leavesdevelopatanytimeduringthegrowingseasonandincludeageneralyellowing(chlorosis)oftheleafandnecrosisoftheleaffromthetipdownward.Plantsalsowilt.Atantopinkrootrotmaydevelopononionand a red to purple discoloration of the stems and bulbs of garlic. A rot develops on basaltissueswheretherootsareattachedtothebulb.Thisrotisusuallywater-soaked(appearswet),tantodarkerbrownincolor,andtissuesusuallyremainfirm.Intime,theinfection can spread up into the bulb causing a soft rot. This results in the plant collapsing anddying.Underwet,humidconditions,afluffywhitetopinkish-redgrowthoffungusmyceliumisproducedondiseasedareas.Bulbsthatshownoobvioussymptomsmay

Figure 10.6 Symptoms of onion smut. Source: WikiGardener


onion, Garlic

stillbeinfectedandrotinstorage.Especiallyunderpoorstorageconditions,thediseasecan result in serious loses in storage.

Ifgrowthofdiseasedplants isstunted,rootsystemisweaklydevelopedanddarkincolor,whiletipsofleavesyellow.Rootsoftheplantsdiseasedduringstorage(leek,greenonion)developnecrosis;falsestalkatthelengthof3to10cmdarkensandrots.Lightorpinkish-redmyceliaappearbetweenleaves.Atthefinalstageofthedisease,damaged tissue becomes wet.

Control


• Croprotation-Ifthediseaseoccurs,usearotationthatexcludestheproductionofonionandgarlicforatleastfouryears;

• Maintain proper storage conditions. Storage facilities should be thoroughlycleanedanddisinfested.Drybulbsbeforeplacementinstorage;

• Storeleeksinsandorwell-drainedsoil,orfreezethem;

• Use resistant or less susceptible varieties if available;

• Use proper agricultural production techniques that minimize damage to theplantand results inhealthyvigorousplants.Avoidwetareas forplantingandpracticesthatresultinexcessivesoilmoisture,suchasoverirrigating.

WhiteRotofOnionandGarlic

Causal agent – Scleriotinia cepivorum. White rot is a major root disease of onion and garlic. Under severe conditions, it can result in complete crop loss. The disease is associated with soil borne inoculum, so infested fields and disease incidence will continue to increase as onions and garlic continue to be produced in infested fields. The fungus produces survival structures called sclerotia. The sclerotia can survive in thesoilwithoutaplanthostfor20yearsormore.Thesclerotiaremaindormantinthesoil until onion or garlic is planted. The roots of onion and garlic produce a substance thatstimulatesthesclerotiatogerminate.Sclerotiagerminateandmyceliumcangrow1to2cmthroughthesoilwheretheypenetratetherootsandbaseofthebulb.Thefungus can spreadbymycelium fromplant toplant if roots are close to eachother.Temperatureisimportantfordiseasedevelopment.Thefungusisnotveryactivewhensoil temperaturesarebelow9°Corabove24°C.Theoptimumtemperature range forinfectionanddiseasedevelopmentis14°to18°C.ThediseaseismostseverewhensoilpHisfrom5.5to6.5.Sclerotiagerminateinmoistsoil,butgerminationisinhibitedinverywetsoils.Bulbonioncropsappeartobeforeseverelyaffectedthandirectseededcropsbecauseofamorevigorousrootsystemearlyintheseason.

DiseaseSymptoms:Diseasesymptomsareobservedbothinthefieldandinstorage.White rot affects the roots and crown of the plant. Above ground symptoms are notobserved in the field until after root infection is well established. Leaves on infected plants turn yellow, wilt, collapse, and eventually die and become brown and dry. Inbadlyaffectedareas,growthofleavesisreducedandgroupsofplantsdierapidly.Whitemyceliumdevelopsondiseasedrootsandthebaseofbulbsincontactwithsoil.Manytiny,black,round,sclerotiameasuringlessthan1mmindiameterformonthemyceliumanddiseasedtissue.Inadvancedstagesofdiseasedevelopment,rootsandbulbsbecomesoftandrottedprimarilyfrominvasionofdiseasedtissuesbysecondarydecayorganisms.

Figure 10.8 Symptoms of white rot of onion. Source:WikiGardener

Figure 10.9 Symptoms of black mold of onion.Author:Paul Cowan

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Thediseasealsodevelopsinstorageandcanresultinseriouslosses.Diseasedbulbsshrinkandbecomelighterincolor.Similarsymptomsareobservedonleekinthefield,near the end of the production period.

Control

• Croplocationisoflimitedvaluebecausethepathogencansurviveinsoilfor20yearsormore.Itisbesttoselectfieldandplantcropswherethereisnohistoryofthedisease.Ifcroprotationisused,itisnotdesirabletogrowonionsorgarliconinfectedlandforatleast10years;

• Sanitation-Removeanddestroyinfectedplantpartsinthefieldandinstorage.Removing infected plant debris and plants from the field will aid in preventing theincreasedbuild-upofsclerotiainthefield;

• Be aware that the sclerotia can survive passing through the digestive tract of animalsandmaybepresentinmanure;

• Useonlydiseasefreetransplants;

• Soilfumigationofheavilyinfestedfieldmaybeuseful,butwillnoteradicatethefungus from the field;

• Fungicides used as onion seed or garlic clove treatments or transplant drenches canbepartiallyeffective;

• Flooding of infested fields has been used to control white rot in some regions of the world.

BlackMoldofOnionBulbs

Causal agent – Aspergilus niger. Black mold of onion is most prevalent in tropical and subtropical production areas where high temperatures favor its development. Black mold can be a problem in the field, but it causes most losses in storage. The pathogenisseedborneinonion.Italsooccurswidelyinfieldsoilsandisasaprophytethatcolonizesdeadplantfoliage.Thefungusgrowsonolddyingonionleavesthengrowstotheneckofthebulbandeventuallyintothebulb.Bulbinfectioninthefieldisusuallyassociatedwithdamagetothefleshyscales.Duringharvesting,sporesofthefungusoninfectedfoliagearereleasedandmovedbyairtootherplantsinthefieldandtoplants innearbyfields.Theoptimumtemperature forgrowth is28° to34°C.Theminimumtemperatureforsporegerminationis17°C.Humiditygreaterthan80percentisrequiredforsporegerminationandthepresenceoffreewaterforsixto12hoursisrequiredforinfection.

DiseaseSymptoms:Thediseaseaffectsonionandgarlicbulbsmostlyduringstorage.Thefunguscausesblack,dustyfungalgrowthonandbetweenthebulbscales.Inseverecasestheentiresurfaceofthebulbmayturncompletelyblack.Theyareuglyandnotmarketable.Severelyaffectedbulbsmayalsorot.Secondarybacterialorganismsusuallycontribute to the rot in storage.

Control

• Use clean, pathogen free seed. If clean seed is not available a fungicide seedtreatment should be used;

• Foliar fungicides can reduce black mold if applied near the end of the season;

Figure 10.10 Onion mosaic virus. Author Paul Cowan


onion, Garlic

• Harvestthecropunderdryconditionsandminimizedamagetothenecktissueof the bulbs;

• Maintaintemperatureandrelativehumidityatappropriatelevelsduringstorage.Monitorthetemperaturewhenusinghightemperaturestodryouttheonionsafterharvest.Temperaturesshouldnotexceed30°to32°Candrelativehumidityshouldbemaintainedbelow80percentaslongaspossible.Longtermstorageatlow temperature stops growth of the fungus, but the fungus can become active attemperaturesabove15°C.

DiseasesCausedbyVirusesOnionMosaicVirus

Causalagent–OnionMosaicVirus.ThediseaseaffectsmanyplantsintheAlliceae family.Plantsmaybeinfectedatallstagesoftheirdevelopment.Theviruscausingthedisease overwinters and moves from crop to crop in infected onion bulbs and garlic cloves.Itcannotsurviveinthesoilforlongperiodsoftime.Hightemperaturesbothinstorageandinthefieldcontributegreatlytoinfectionanddiseasedevelopment.Thevirusistransmitted(vectored)byvarioustypesofmites,nematodesinthesoil,andthefour-leggedgarlicmite.

DiseaseSymptoms:Thediseasemostlydamages leavesand spadix, andcancausecroplossesupto20to25percent.Diseasedleavesorspadixbecomecoveredwithlightyelloworlightgreenspotsinamosaicpattern.Ingarlic,thespotscoverthewholelengthof the leaf. With time, chlorosis develops and wilting of the leaves occurs. The disease can also causedeformationof the leaves. Flower stalks alsodevelop clearly visiblemosaicsymptoms.Inonion,infectedplantsoftenproduceunripebulbsthatarenotmarketable.

Control

• Maintain optimal storage conditions;

• Usehealthyvirusfreeseedmaterial;

• Control insect, mite, and nematode vectors that transmit the diseases.

DiseasesCausedbyBacteriaBacterialSoftRot(Bacteriosis)

Causal agents – Pectobacterium carotovorum and Burkholderia cepacia. The disease can result in serious losses in the field during storage.

Disease Symptoms: Disease mostly affects plant that is weakened as a result ofunfavorable climatic conditions or poor agricultural practices. In onion, the diseasemaydevelopbothinthefieldandinstorage.Asinfectedbulbsreachmaturity,slightlysunken, softareasdevelopon thebulb thatareclearlydifferent fromhealthy tissue.Damaged layers aredarkgray,water-soakedand soft. Eventually, infectedbulbs canturnintoasoftrottedmassoftissuewithaveryunpleasantodor.Atypicalsymptomofthisdiseaseisalternatinghealthyanddamagedlayersinthebulb.

Bacteriosis damage on garlic during storage is manifested as sunken ulcers or areas ongarliccloves.Damagedclovetissuedevelopsapearly-greenishcolorandmayappearlikeit’sfrozen.Infectedgarlicclovesalsohaveanunpleasantodor.

Figure 10.11 Symptoms of bacterial soft rot in onion. Source: Keith Foster Blog

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Control


• Usehealthy,disease-freeseedmaterial.

PhysiologicalDisordersOnion and garlic are prone to physiological disorders. One of these disorders is

doubling or splitting of the bulb. This condition is caused by genetic, cultural, andenvironmentalfactors.Over-fertilization,unevenwatering,andtemperaturefluctuationsareallbelievedtoinfluencedoublebulbformation.Somevarietiesaremorepronetoproduction of double bulbs than others. Varieties prone to doubling should be seeded ortransplantedsevento10daysearlierinordertominimizethedisorder.

Bothonionandgarlicarebiennials,formingbulbsthefirstyear,whichserveasfoodsourceforplantgrowthandfloweringthefollowingyear.Theprocessofflowering iscalled bolting. Under cool temperature during the latter part of the growing season a seedstalk,bolt,orscopeformsveryquickly.However,plantswithlargebulbsmayboltinthefirstyearifappropriateenvironmentalconditionsaremet.

Greening occurs when actively growing onion and garlic bulbs are exposed tosunlight for an extended period of time. Hilling (covering the bulbs with soil) andconditions that encourage strong healthy leaves, such as early fertilizer application,shades the bulb during development. Sunscald is another disorder that affects onion bulbs,andtoalesserextentgarlicbulbs;itoccurswhenthebulbshavereachedmaturitybutharvest isdelayed.Thisdisorderoccursattheshoulderofmostonionbulbsthatareexposedtosunlightforanextendedperiodoftime.Scalesseverallayersdeepwilldryandturnbrown.Undersevereconditions,theinternaltissuemayactuallydieandbecome soft and translucent.

Translucentscaleisaphysiologicaldisordersimilar inappearancetofreezeinjury.Thebigdifferenceisfreezeinjurywillalwaysaffecttheouterscaleswhereastranslucentscalemayfirstappearonscalesseveral layersdeepinthebulb.Translucentscaleisapost-harvestphenomenon causedby exposure tohighCO2 during storage facilities. Thisismostlikelytooccurinrefrigeratedstoragewithoutadequateventilation.

Harvesting and storage

Matureonionandgarlicbulbsmaybeharvestedwhenthetopsstarttodry.Thisisusuallyinlatesummerorearlyfall.Bulbsshouldbedugupratherthanpulledtoavoidinjury.Allowthetopstodryeitherinwindrowsinthefieldorindoorifthefieldiswet.It isessential thatonionandgarlicbulbsarewellcuredbefore theyarestored.Cureharvestedbulbfor10-14daysinasunny,well-ventilatedarea.Alignonionssothattheleaves of one onion cover the bulb of another.

Mature bulbs are best stored at 0°C. Garlic stores well under a wide range oftemperatures,butsproutsareproducedquicklyat5°Corhighertemperature.Storagehumidity shouldbemaintained at 65 to 70percent at all times to discouragemolddevelopment and root formation. Onion and garlic bulbs will keep for up to sevenmonthscuredandstoredatidealtemperatureandhumidity.


Watermelon Citrulluslanatus belongs to the Cucurbitaceae family, which includescantaloupe, muskmelons, pumpkin, squash, and cucumber, among several others.Watermelon fruits are very popular worldwide, especially during the hot summermonths,fortheirrefreshingtasteandflavor.

PollinationRequirements

Watermelonandothermembersofthesamefamilyproducebothmaleandfemaleflowersonthesameplant.Thefirstflowersproducedbyeachplantareusuallymales.Dependingonweatherconditionandthehealthoftheplants,femaleflowersstarttoappearwithinaboutsevento10daysfromthestartofflowering. It isestimatedthatonlyoneoutofeverysevenflowersonashootisafemale.Mostmaleandfemaleflowersusuallyabortbeforepollinationtakesplacecausingfruitsettobeirregularthroughouttheseason.Thenumberoffruitsalreadysetontheplantanditshealthdeterminethenumberoffemaleflowersthatsetintofruitslateron.Therefore,removingmisshapedanddamagedfruitswhentheyaresmallisimportantinordertoencouragemorefemaleflowerstodevelopandsetfruits.Flowersopenforonlyashorttime,onetotwohoursaftersunrise,thencloseintheafternoon,butnevertoreopenagainregardlessiftheyhavebeenpollinatedornot.Honeybeesandother insectsarerequired foradequatepollinationandfruitset.Usuallyfourtofivehivesperhectareareneeded.Beesmustdropadequatepollengrainsonallthreelobesofthefemaleflowerstigmainordertoreducetheriskofproducingamisshapenfruit.Cold,rainyandwindyweatherreducethebee’sactivity,whichcancausepoormelonproductionduetoinadequatepollination.Poor pollination reduces the number of seeds per fruit, which results in a reduction in fruit size and slowing down of the ripening process.

Seedless watermelons are becoming more popular in the US and Europe. Seedless watermelonsarenotexactlyseedless,theirseedsdevelopbuttheydonotgrowintofullsize.Seedlesswatermelonsaresterile(Triploid),however,theydoneedtobepollinatedwith viable pollens preferably from a seeded variety in order for the fruits to grow.Usuallyoneseededvarietyshouldbeplantedwitheveryfivetosixseedlessvariety,oronerowtoeverythreetofourrowsshouldbetheseededvariety.Itisbettertoselectaseededvarietywithadifferentcolorinordertobeabletodistinguishbetweentheseeded and seedless varieties at harvest.


Watermelonsareverysensitivetocoldandfrostconditions.Theypreferhotanddryclimate.Plantscantolerateaminimumof18°Candamaximumof35°Ctemperatures,buttheygrowbestattemperaturesinbetween.Theoptimumsoiltemperatureforrootgrowthisintherangeof20°to35°C.Transplantsshouldnotbemovedintothefielduntilthesoil temperatureat6 to7cmbeneaththesoilsurfacereachesabout15° to16°C.Fruitsgrownunderhotanddryconditionshavehighersugarcontentthanthosegrownunder cooler and humid conditions.

SoilRequirement

Watermelonsgrowbestonsandyloamwithhighorganicmatter,goodwaterholdingcapacity,withadequateairandwaterinfiltrationrates.OptimumsoilpHisbetween5.8and6.6. Lower soil pHenhances thedevelopmentofblossomend rot,whilehigher

Watermelon

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soilpHenhancesironchlorosis.Watermelonsarehighwater-requiringplants.Keepinga constant supply ofmoisture during the growing season is essential for good fruitsize.However,excesswateratanytimeduringcropgrowth,especiallyasfruitreachesmaturity, can cause the fruit to crack,whichwill reduce crop yield and fruit quality.Commercial growers prefer to grow watermelons on raised beds using drip irrigation.

PlantingandFertilizationRequirements

Commerciallygrownwatermelonsstartfromtransplantsoraredirectlyseededinthefield.Transplantstakefourtosixweeksofgrowthundercontrolledenvironmentbeforetheyarereadyforfieldplanting.Onaverageapproximately7,000to12,000plantsaretransplantedperhectareinsinglerows/hillsspacedat200cmapartand200to250cmbetweenplantsintherow,withsomeadjustmentsforvigor.Insomecountriesgrowersdirectseedwatermelonsinhills(twotothreeseedsperhill).However,directseedingtakesalongertimeforthefruittoreachfullmaturity,whichreducespotentialincomefromearlyharvest.

Fertilizer rates should be based on annual soil test results. The general fertilizer recommendationistosidedresssoonaftertransplantingwithabout44kgperhectarenitrogen and 60 kg per hectare of each of potassium and phosphorous. Anotherapplication of similar amounts needs to be applied either through drip or side dressing assoonasthefirstmaleflowersstarttoform.

Harvest and Storage

It isdifficulttoknowwhenfruitsarereadyforharvest.Also,watermelonfruitsdonotcontinueto ripenafterharvest.Usually it takesabout three to fourmonthsafterplanting for the fruit to reach fullmaturity, depending on the cultivar andweatherconditions.Multiple pickings are usually needed, because each fruit is pollinated atdifferent times.Fruits shouldbeharvestedat fullmaturity forbest tasteandtexture.Indicatorsofwatermelonmaturityincludeayellowspotonthefruitsurfaceincontactwith soil or plastic mulch; a brown, dried tendril where the fruit stem is joined to the watermelon vine; and a dull surface on top of the fruit. Because individual fruits are pollinatedatdifferenttimes,multipleharvestsareusuallynecessary.

Fruitsshouldbeharvestedatthecoolestpartofthedaywhichisusuallyveryearlyinthemorning.Damagedormisshapedfruitsshouldbediscardedtoensuregoodqualityfruits reach the consumer. Fruits should be moved out of the field and into a shaded area or cold storage as soon as possible. Keeping fruits in the sun or not cooling them reducestheirquality.Fruitsshouldbecooledtobetween9°and14°Cand85-90percentrelativehumidity.Watermelonswillmaintaingoodqualityforabout20-25daysifstoredproperly.

DISEASESOFWATERMELONWatermelon is affectedby several importantplantdiseases inGeorgia.Themost

importantdiseasescausedby fungi include:whitemold (sclerotiniosis),anthracnose,downymildewandpowderymildew.Watermelonmosaicvirusandcucumbermosaicvirusarethemostimportantdiseasescausedbyvirusesandbacterialwiltisthemostimportantdiseasecausedbybacteria.


Watermelon

DiseasesCausedbyFungiWhiteMold(Sclerotiniarot)

Causal agent – Sclerotinia sclerotiorum. White mold (sclerotinia rot) has beenobserved worldwide and is one of the most destructive and widespread disease of horticultural crops worldwide. However, the disease is considered a minor problem on cucurbits inmany regions.When thediseasedoesoccurunder conditions favorablefor disease development, it can result in serious losses. The fungus survives in soil as sclerotiaandmyceliuminplantdebrisbothontopofandinthesoil.Thesclerotiacansurviveinsoilintheabsenceofplantdebris.Thediseaseisfavoredbylowtemperaturesandprolongedwetperiods. Infectionstendtooccur indeadtendrilsandpetiolesorthroughwitheredflowersstillattachedtodevelopingfruit.Thefunguscancausefruitrot both in the field and postharvest.

Disease Symptoms: White mold first develops on the flower, leaves, stems andfruit. Infected tissues often become coveredwith a cottonywhite growth of fungalmyceliumandsclerotiamayalsodevelop.Steminjuriescanprovideentrypointsforthefungus,whichspreadsthroughthestem,producingmyceliumandsclerotia inside it.Symptomsonfruitvaryfromnonetoawater-soakedappearance,andacottonywhitegrowthofmyceliumandsclerotiamaydevelopwherethefruitisincontactwiththesoil.Occasionallydiseasedfruitdryandbecomemummified.Internalsymptomsappearassoft or wet rot with numerous sclerotia.

Control

• Croprotationmaybeoflimitedbenefitbecauseofthewidehostrangeofthepathogenandtheproductionofsclerotiathatcansurviveinthesoilforrelativelylong period of time;

• Sanitation-Removeanddestroyinfectedplantsandfruitsfromthefield;

• There are reports that deep plowing and careful irrigation management can aid in controlling disease incidence;

• Thetimelyapplicationofeffectivefungicidesmayaidindiseasecontrol,butitisdifficulttogeteffectivefungicidecoveragewherethefruitorotherplantpartsare in contact with the soil.

Anthracnose

Causal agent – Colletotrichum orbiculare. Anthracnoseoccursworldwideonmanycucurbit crops and several cucurbit weeds. The fungus over winters on infected crop residues, volunteer cucurbit plants and cucurbit weed species. Conidia from these sourcesmovetouninfectedplantsbysplashingwaterfromrainofoverheadirrigation,contaminatedtoolsandworkers,andpossiblyinsects.Togerminateandinfecttheplant,conidiarequire24hoursof100percentrelativehumidityandoptimumtemperaturesof22°to27°C.Sporescantakeupto72hourstoinfectandfirstsymptomsappearatfourdaysafterinfection.Thepathogencanalsobeseedborneandresultinearlyinfectionson germinating seedlings or transplants placed into production fields.

DiseaseSymptoms:Firstsymptomsappearasirregularlyshapedwater-soakedleaflesionsthatsoonturnchlorotic(yellow).Lesionscanexpandtobecomegreaterthan1cmindiameterandappeardarkbrowntoblack.Lesionscancovermostoftheleafmakingitbecomedistorted.Tissuesinlesionsdry,crack,andfallout.Lesionscanalso

Figure 11.2 Symptoms of anthracnose lesion on watermelon fruit. Source: Purdue University

Figure 11.1 Symptoms of white mold on watermelon.Source: University of Delaware

Figure 11.4 Symptoms of powdery mildew on leaves. Source: Télédétection et SIG en Agriculture

Figure 11.3 Symptoms of downy mildew in watermelon fruit and leaves. Source: Brooks Country Ag Connection

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occuronpetiolesandstemsandappearaselongated,ovaltodiamondshaped,water-soakedlesionsthatturntantobrownincolor.Stemlesionscanbecoveredwithtinyblackfungalfruitingstructures(acervuli)andpinksporemassesthatareexudedfromthesestructures.Fruitsymptomsarecircularwater-soakedareasthatlaterbecomedarkbrown to black sunken lesions. Acervuli and pink spore masses will also develop on fruit lesionsduringwetperiodswithhighrelativehumidity.

Control

• Useresistantvarietiesiftheyareavailable;

• Use clean seed that does not have significant levels of the pathogen;

• Practice crop rotation in which cucurbit crops are not planted for at least two years;

• Avoidtheuseofoverhead irrigation,especially if thedisease ispresent in theplanting;

• Thetimelyuseofeffectivefungicidescanaidgreatlyincontrolofthisdisease.

DownyMildew

Causal agent – Рseudoperonospora cubensis. Pseudoperonospora cubensis is an oomyceteandanobligateparasite.Itcannotsurviveintheabsenceofalivinghostsuchassusceptiblecucurbitcropsandweedspecies.Infectedplantsarethemainsourceofinoculum for starting the disease. The spores that cause infection can be spread over greatdistancesbywind.Spores(sporangia)areproducedoninfectedtissueifhumidityisat100percentforsixhoursandthetemperatureisbetween15°to20°C.Thesesporesareblowninwindorsplashedontosusceptibletissuewheretheygerminateandinfectiffreewaterispresentforatleasttwohoursat20°to25°C.Symptomsmayappearinthreeto12days.

Disease Symptoms: First symptoms are small, pale green angular or rectangularspots that develop on the upper leaf surface. These spots on the upper leaf surface laterturnchlorotictobrightyellow.Asthespotsage,theybecomebrownandnecrotic(dead).Severeleafinfectioncanresultinshrivelinganddeathoflargeareasoftheleaf.Underconditionsofhighhumidity,thesurfaceofthespotsontheundersideoftheleafcanbecomecoveredwithagrowthoflightgraytodarkpurplefungusmyceliumandspores.Downymildewcancausestuntingordeathofyoungplantsifinfectionoccursearlyandissevere.Fruitmaturationandproductioncanbepreventedandfruitflavorand sugar content can also be affected if infection is severe.

Control

• Avoidusingoverheadirrigation,especiallyifthediseaseispresentintheplanting;

• Thetimelyuseofeffectivefungicidesisimportantforcontrollingthisdisease.

PowderyMildew

Causalagent–Erysiphecichoracearum,Sphaerotheca fuliginea.Powderymildewisaverycommondiseaseofmostcucurbitcropsworldwide.Severalpowderymildewfungiinfectvariouscucurbitcrops.Ifnotcontrolled,thediseasecancauseearlyplantsenescence,a reduction inyieldandevendeathof theplant.Powderymildewfungi


Watermelon

are all obligate parasites that cannot survive in the absence of a living host plant. Theyoverwinterorsurviveoncucurbitcropplants inthefield,volunteercropplantsorcucurbitweedspecies.Conidiaofthefunguscanbeblownoverlongdistancesbywind.Unlikemostother fungalplantpathogens, theconidiaofpowderymildewdonotrequirefreewatertogerminateandinfecttheplant.Infact,freewatercaninhibitpowderymildewdevelopment.Conidiarequirehighrelativehumiditytogerminateandinfectplants;however,conidiacangerminateandinfectat50percentrelativehumidityorlower.Diseaseddevelopmentisoptimumattemperaturesof20°to27°C.

DiseaseSymptoms:Thefirstsignofthepathogenisawhite,powderygrowthofthefungus that develops on the upper and lower surface of the leaf, and on leaf petioles andstems.Symptomsfirstdeveloponolderleaves.Inseverecasestheentireleafcanbecoveredwiththewhitegrowth,turnbrownanddie.Severelyinfectedplantscanbestunted,havesmallerfruitandreducedyields.Fruitfromseverelyinfectedplantsmayhavelesssugarcontent,poorflavoranddeformedshape.

Control

• Plant resistant or less susceptible varieties if available;

• The timely application of effective fungicides is important for controlling thisdisease.

DiseasesCausedbyVirusesWatermelonMosaicVirus(WMV)

Causal agent – Watermelon mosaic virus.Watermelonmosaicvirus(WMV)isfoundin cucurbit producing areas throughout the world. WMV infects cucurbits. Legumes and manyotherplantsandhasahost rangeofover150species.Thevirussurvives fromseason to season in infected crop plants and susceptible weed species. The pathogen is vectoredbyaphids.

DiseaseSymptoms:WMVcausesleavestodevelopmosaicpatternsoflightyellowandlightgreenpatchesandsometimesring-shapedspotsareproduced.Whenseverelyinfected, leavescanbecrinkled.Fruitmaybedistortedorhavevariations (breaks) insurfacecolor.Fruitmayalsodeveloptumorsandspots.Severelyinfectedplantsmaybestunted.

Control

• Control volunteer cucurbit crop plants and weeds pieces in and near the painting that can serve as a source of the virus;

• Sanitation-Removeanddestroyinfectedplantpartsandfruitsfromthefield;

• Control aphid vectors that spread the virus with effective insecticides.

CucumberMosaicVirus(CMV)

Causal agent – Cucumber mosaic virus. CMV is commonly found throughout theworld and infects over 800plant species including cultivated cropplants andmanyweedspecies.Itisprobablythemostcommonlyencounteredvirusoncucurbitcrops.CMVistransmittedbyanumberofaphidspeciesandcommonlysurvivesinmanyweedspecies. CMV can also be seed borne.

Figure 11.5 Symptoms of watermelon mosaicvirus. Source: Ephytia Inra

Figure 11.6 New growth on watermelon with CMV. Author: G. Brust

Figure 11.7 Symptom of bacterial fruit blotch in watermelon fruit. Author: E. Lookabaugh

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DiseaseSymptoms:CMVcanseverelystuntplantgrowthandcauses leavestobedistorted (developbubble-likeulcers andwrinkles), reduced in size, curledor rolled,andshowamosaicormottledpatternoflightyellowandlightgreenpatches.Flowerscanbedistortedandmayhavegreenpetals.Fruitcanbesmall,malformed,andhavevarious discolorations. The disease is especially common on protected soil (in hightunnelsorgreenhouses).

Control

• Always use disease free seed and plantingmaterial. If infected seedmust beused,seedtreatmentishighlyrecommended.Heattreatmenthasbeenshowntobeeffectiveforneutralizingthevirus.Seedmaterial,isinitiallyheatedatthetemperatureof50°C,forthreedaysandnightsandafterwardsatthetemperatureof78°to80°C,for10seconds;

• Control aphids that spread the virus with effective insecticides;

• In high tunnels and greenhouses (protected soil), maintain the appropriatetemperature regime;

• Control volunteer cucurbit crop plants and weeds that can serve as source for the virus in and near the planting;

• Usediseaseresistantvarietiesorhybridswhenavailable.

DiseasesCausedbyBacteriaBacterial Fruit Blotch

Causal agent – Acidovorax avenae. ssp. Citrulli. Bacterial fruit blotch is a veryimportant disease on watermelon. The bacteria can overwinter in watermelon rinds and other plant debris in the field, volunteer watermelon plants and other infected cucurbits,includingmanyweedspecies.Thebacteriaarealsoseedborneandcommonlyinfect transplants.The pathogenmay also be transmitted by contaminatedworkersandequipment.Thediseasedevelopsrapidlyundermoist(wet)andwarmconditions.The pathogen is splashed dispersed and infection can occur with leaf wetness periods ofonly30minutesattemperaturearound26°C.Whenthediseaseissevere,upto80percent of the fruit can be lost.

DiseaseSymptoms:Acharacteristicsymptomofbacterialfruitblotchisadarkolivegreen stain or blotch on the upper surface of the fruit. The blotch is first noticeable as a smallwater-soakedarea,lessthan1to2cmindiameter.Latertheblotchrapidlyexpandsto covermuchof the fruit surfacewithin seven to10days.As theblotches increaseinsize,theareaaroundtheinitialinfectionsitebecomesnecrotic(dead).Inadvancedstages of disease development, the skin of the rind ruptures and often a transparent or amber-coloredsubstanceisexuded.Colonizationofthefruitbysecondaryorganismsresults in fruit rot and collapse of the entire fruit. The pathogen is seed borne and is commonlytransmittedoninfectedtransplants.Thefirstsymptomsonseedlingsareawater-soakedareaontheundersideofthecotyledons.Asthecotyledonsexpandthelesionsbecomenecrotic. Lesionsalsodeveloponyoung leavesandappearas small,darkbrownareaswithachlorotic(yellow)marginorhalo.

Figure 11.8 Symptoms of blossom end rot of watermelon. Source: Minesota Ministry of Agriculture


Watermelon

Control

• Alwaysusehealthy(pathogenfree)seedsandtransplants;


• Sanitation-Removeanddestroyinfectedplantsandfruitsfromthefield.

PhysiologicalDisordersBlossom End Rot

Watermelons fruits are susceptible to development of blossom end rot (BER). Asmentioned earlier in tomatoes and peppers, blossom end rot is related to calcium deficiency, moisture fluctuation, and stress. Prevention recommendations includeadequateamountsofcalcium,propersoilpH (6 to6.5),andauniformandsufficientsupplyofmoisture.TheincidenceofBERusuallyvariesfromseasontoseasonandtendstoaffectoblongvarieties(CharlestonGraytype).Fruitsthathaveblossomendrotareconsidered unmarketable.

Hollow heart and white heart

These two physiological disorders are influenced by genetics, environment, andseveral other nutritional and non-nutritional factors. To ensure fewer incidences ofthedisorders,plantonlycultivarsthathavesomedegreeofresistance.Inaddition,thecrop should be grown under optimal nutrient management and moisture conditions. Application of high nitrogen and low calcium during fruit development encourages the developmentofthedisorder.Alsofluctuationofwateringanddroughtcanincreasetheproblem.

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MelonsareveryimportantmembersoftheCucurbitaceaefamily.Generally,melonshavethesameculturalrequirementsaswatermelons.Refertothewatermelonsectionfor more detailed information. The most important melons grown in the world are muskmelonsand/orcantaloupe.

Planting Methods

DirectSeeding

Muskmelonsmaybeplantedbydirectseedingorbytransplantsafterthedangeroffrosthaspassed.Theoptimumtemperaturerangeforseedgerminationisbetween21°and35°C.Directseededmelonsshouldbesownwhenthesoil temperature isabove18°C.Itisimportanttousefungicide-treatedseed,becausemuskmelonsaresensitivetodampingoff,especiallyundercool,wet,soilconditions.Sowseedatadepthof13to25mm.Seedingwillrequire2.2to4.4kgofseedperha(16,000to20,000seedsper454g),unlessaprecision-typeseederisbeingused.

Transplanting

The use of transplants can reduce seed cost compared to direct-seeding andresultinearlierproduction,especiallywhenusedwithpolyethylenemulch.Seedingfor transplant productions should be done two to four weeks prior to date of transplanting.

Varieties

In theUnited States,muskmelons are classified into twogroups, Eastern shippersand Western shippers.

1. Easternshippers-Fruitsareroundtoovalinshapewithsuturesandnettedrind.Flesh of this group is soft which makes them more suitable for local markets.

2. Westernshippers -Fruitsarealso round toslightlyoval in shape,withheavilynettedbutsuture-lessrind.Fruitsinthisgrouphavefirmflesh,whichmakethemsuitable for storage and long distance shipping.

Withineachof these twogroups therearemanycommerciallyavailablevarietiestochoosefrom.Itisbesttoselectafewseedsofsomeofthesevarietieseachyearandplantthematyourfarmbeforedecidingwhattogrowonalargescale.Therearesomevarietiesthatareresistanttoimportantdiseaseswhileothersareverysensitivetosulfur.Sobeawarethatifyouusesulfurfordiseasecontrolyoumustavoidtheuseofsulfursensitivevarietiesorplantinjurycanbesevere.yourlocalseeddistributorshouldtellyouifthevarietyofyourchoiceissensitivetosulfur.

Inadditiontomuskmelons/cantaloupes,thereareseveralspecialtymelonsthatmayalsohaveagoodmarketinGeorgia.Thefollowingisalistofsomeofthesegroups.

• Honeydewmelons. Fruits in thisgrouphave smoothandgreen-to-white rind,turningcreamyincolorwhenripe.Thefleshiscream,lightgreen,ororangeincolor.Fruitsusuallyweighbetween1to2kg.Seedsgerminatebestwhenthesoiltemperatureisbetween30°to35°C.Fruitsmaturebetween70to80daysfrombloom.

Melon


Melon

• Casaba melons.Casabamelonhasaverythickrind,andtheexternalappearanceofthefruitdiffersfromthatofthehoneydewandthecantaloupe.Theskinofacasabaissmooth,butwrinkled,withlongitudinalfurrows.Rindcolorisusuallyyellowtogreenishyellow.Thefruit isnotassweetasmuskmelonbut itstoresverywell.Fruitsweighbetween3to3.5kg.

• Crenshaw melons. When ripe, Crenshaw melons are roughly ovoid, with agreenish-yellow,slightlyribbedskin.Thefleshisarichpinkish-orangecolorwithalargeseedcavityandaverysweetflavor.Fruitarelatematuring.Fruitsweighbetween3to4kg.

• Canarymelons.Thesemelons are very sweetwith a distinctive flavor. Rind isbrightyellowandthefleshispalegreentowhitewithapaleorangeseedcavity;Fruitislatematuringrequiringbetween80to90daysafterbloom.Plantsneedplentyofheattoreachmaturity.Fruitsweighbetween2to3kg.

• Charente’s. ApopularEuropeanmelon,alsoknownasFrenchor Italianmelon.Rindissmoothandslightlynettedwithagreentograyishcolor.Flesh isdeeporange,firm,andsweet.Fruitisroundandrelativelysmall,weighing0.5to1kg.

DISEASESOFMELONSMelons are affected by several important plant diseases in Georgia. The most

important diseases caused by fungi include: powdery mildew, Fusarium wilt,anthracnoseanddownymildew.Watermelonmosaicvirusandcucumbermosaicvirusarethemost importantdiseasescausedbyvirusesandbacteria leafspot isthemostimportantdiseasecausedbybacteria.

DiseasesCausedbyFungiPowderyMildew

Causal agent – Sphaerotheca fuliginea. Powderymildewisaverycommondiseaseofmostcucurbitcropsworldwide.Severalpowderymildewfungiinfectvariouscucurbitcrops. Ifnot controlled, thediseasecancauseearlyplant senescence,a reduction inyieldandevendeathoftheplant.Powderymildewfungiareallobligateparasitesthatcannot survive in the absence of a living host plant. They overwinter or survive oncucurbit crop plants in the field, volunteer crop plants or cucurbit weed species. Conidia ofthefunguscanbeblownoverlongdistancesbywind.Unlikemostotherfungalplantpathogens,theconidiaofpowderymildewdonotrequirefreewatertogerminateandinfecttheplant.Infact,freewatercaninhibitpowderymildewdevelopment.Conidiarequire high relative humidity to germinate and infect plants; however, conidia cangerminateandinfectat50percentrelativehumidityorlower.Diseasedevelopmentisoptimumattemperaturesof20°to27°C.

DiseaseSymptoms:Thefirstsignofthepathogenisawhite,powderygrowthofthefungus that develops on the upper and lower surface of the leaf, and on leaf petioles andstems.Symptomsfirstdeveloponolderleaves.Inseverecasestheentireleafcanbecoveredwiththewhitegrowth,turnbrown,anddie.Severelyinfectedplantscanbestunted,havesmallerfruitandreducedyields.Fruitfromseverelyinfectedplantsmayhavelesssugarcontent,poorflavoranddeformedshape.

Figure 12.1 Symptoms of powdery mildew in melons. Source: Specialty Cropportunities

Figure 12.2 Symptoms of fusarium wilt. Source: Specialty Cropportunities

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Control

• Plant resistant or less susceptible varieties if available;

• The timely application of effective fungicides is important for controlling thisdisease.

Fusarium Wilt

Causalagent–Fusariumoxysporum.ThediseasecycleofFusariumwiltofmelonisalmostidenticaltoFusariumwiltonwatermelon.Spreadofthepathogenoccursmainlyfrom movement of infested soil and plant debris. The fungus can also be seed borne. The funguscansurvive in soil as spores (chlamydospores) for relatively longperiodsThe fungus can colonize crop residues and roots of most crops that would be grown in rotationwithmelon;therefore,croprotationisnothighlyeffectiveforcontrollingthedisease.Diseaseseverityismaximumatsoiltemperaturesof18°to25°Canddeclinesrapidly at temperatures above 30°C. At high soil temperatures, plantsmay becomeinfected but may not wilt. Instead, yellowing and severe stunting may occur. Highnitrogen,particularlyintheformofNH4,andlight,sandy,slightlyacidicsoils(pH5.0to5.5)favordiseasedevelopment.

DiseaseSymptoms:SymptomsofFusariumwiltofmelonareverysimilartothoseofFusariumwiltofwatermelon.Themostcommonsymptomisageneralyellowingoftheleavesandasporadic(scattered)occurrenceofdiseasedplantsinthefield.Plantsmaybeaffectedatanystageofdevelopment.Infectedseedlingmaydeveloprootrot,dampenoffanddie.Inolderplants,theolderleavesturnyellow,andoneormorestems(runners)wilt.Incertaincases,suddenwiltingoftheplantmayoccurwithoutanyyellowingofleaves.Wiltingmayoccurononlyonesideoftheplant,andalesionmaydeveloponthebaseofthestemnearthecrownextending20to50cmupthestem.Oncetissuesaredead,thefungusmaygrowonthesurfaceofinfectedplantpartsproducingawhitematoffungalgrowth(mycelium)onthesurface.Infectedplantsdryupanddie.

Control

• Selectanduseresistantorlesssusceptiblevarietiesiftheyareavailable;

• AdjustingsoilpHwithlimeto6.5to7.0andreducingthelevelofnitrogeninthesoil can aid in disease control;

• Sanitation- Remove and destroy infected plants and plant debris from theplanting.

Anthracnose

Causal agent – Colletotrichum orbiculare. Anthracnoseoccursworldwideonmanycucurbit crops and several cucurbit weeds. The fungus overwinters on infected crop residues, volunteer cucurbit plants and cucurbit weed species. Conidia from these sourcesmovetouninfectedplantsbysplashingwaterfromrainofoverheadirrigation,contaminatedtoolsandworkers,andpossiblyinsects.Togerminateandinfecttheplant,conidiarequire24hoursof100percentrelativehumidityandoptimumtemperaturesof22°to27°C.Sporescantakeupto72hourstoinfectandfirstsymptomsappearatfourdaysafterinfection.Thepathogencanalsobeseedborneandresultinearlyinfectionson germinating seedlings or transplants placed into production fields.

Figure 12.3 Symptoms of anthracnse in melons. Author: Thomas. A. Zitter


Melon

DiseaseSymptoms:Firstsymptomsappearasirregularlyshapedwater-soakedleaflesionsthatsoonturnchlorotic(yellow).Lesionscanexpandtobecomegreaterthan1cm indiameterandappeardarkbrowntoblack.Lesioncancovermostof the leafmakingitbecomedistorted.Tissuesinlesionsdrycrackandfallout.Lesionscanalsooccuronpetiolesandstemsandappearaselongated,ovaltodiamondshaped,water-soakedlesionsthatturntantobrownincolor.Stemlesionscanbecoveredwithtinyblackfungalfruitingstructures(acervuli)andpinksporemassesthatareexudedfromthesestructures.Fruitsymptomsarecircularwater-soakedareasthatlaterbecomedarkbrowntoblacksunken lesionsandusuallydevelopas the fruitapproachesmaturity.Acervuli and pink spore masses will also develop on fruit lesions during wet periods withhighrelativehumidity.

Control

• Useresistantvarietiesiftheyareavailable;

• Use clean seed that does not have significant levels of the pathogen;


• Avoidtheuseofoverhead irrigation,especially if thedisease ispresent in theplanting;

• Thetimelyuseofeffectivefungicidescanaidgreatlyincontrolofthisdisease.

DownyMildew

Causal agent – Pseudoperonospora cubensis. Pseudoperonospora cubensis is an oomyceteandanobligateparasite.Itcannotsurviveintheabsenceofalivinghostsuchassusceptiblecucurbitcropsandweedspecies.Infectedplantsarethemainsourceofinoculum for starting the disease. The spores that cause infection can be spread over greatdistancesbywind.Spores(sporangia)areproducedoninfectedtissueifhumidityisat100percentforsixhoursandthetemperatureisbetween15°to20°C.Thesesporesareblowninwindorsplashedontosusceptibletissuewheretheygerminateandinfectiffreewaterispresentforatleasttwohoursat20°to25°C.Symptomsmayappearinthreeto12days.

Disease Symptoms: First symptoms are small, pale green angular or rectangularspots that develop on the upper leaf surface. These spots on the upper leaf surface laterturnchlorotictobrightyellow.Asthespotsage,theybecomebrownandnecrotic(dead).Severeleafinfectioncanresultinshrivelinganddeathoflargeareasoftheleaf.Underconditionsofhighhumidity,thesurfaceofthespotsontheundersideoftheleafcanbecomecoveredwithagrowthoflightgraytodarkpurplefungusmyceliumandspores.Downymildewcancausestuntingordeathofyoungplantsifinfectionoccursearlyandissevere.Fruitmaturationandproductioncanbepreventedandfruitflavorand sugar content can also be affected if infection is severe

Control

• Avoidusingoverheadirrigation,especiallyifthediseaseispresentintheplanting;

• Avoidplantingnewplantingsclose toplantings thatare infectedwithdownymildew;

• Thetimelyuseofeffectivefungicidesisimportantforcontrollingthisdisease.

Figure 12.4 Symptoms of downy mildew in melons. Source: Ontario Ministry of Agriculture, Food and Rural Affairs

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DiseasesCausedbyVirusesCucumberMosaicVirus(CMV)

Causal agent – Cucumber mosaic virus. CMV is commonly found throughout theworld and infects over 800plant species including cultivated cropplants andmanyweedspecies.Itisprobablythemostcommonlyencounteredvirusoncucurbitcrops.CMVistransmittedbyanumberofaphidspeciesandcommonlysurvivesinmanyweedspecies.CMVcanalsobeseedborneandiseasilytransmittedmechanicallyfromplanttoplantonworkershandsorequipment.

DiseaseSymptoms:CMVcanseverelystuntplantgrowthandcauses leavestobedistorted(developbubble-likeulcersandwrinkles),reducedinsize,curledorrolled,andshowamosaicormottledpatternoflightyellowandlightgreenpatches.Flowerscanbedistortedandmayhavegreenpetals.Fruitcanbesmall,malformedandhavevariousdiscolorations.Thediseaseisespeciallycommononprotectedsoil(inhightunnelsorgreenhouses).

Control

• Always use disease free seed and plantingmaterial. If infected seedmust beused,Seedtreatmentishighlyrecommended.Heattreatmenthasbeenshowntobeeffectiveforneutralizingthevirus.Seedmaterial,isinitiallyheatedatthetemperatureof50°C,forthreedaysandnightsandafterwardsatthetemperatureof78-80°Cfor10minutes

• Control aphids that spread the virus with effective insecticides;

• In high tunnels and greenhouses (protected soil), maintain the appropriatetemperature regime;

• Control volunteer cur bit crop plants and weed that can serve as source for the virus in and near the planting;

• Usediseaseresistantvarietiesorhybridswhenavailable.

WatermelonMosaicVirus(WMV)

Causal agent – Watermelon mosaic virus. Watermelonmosaicvirus(WMV)isfoundin cucurbit producing areas throughout the world. WMV infects cucurbits, legumes and manyotherplants,andhasahostrangeofover150species.Thevirussurvivesfromseason to season in infected crop plants and susceptible weed species. The pathogen is vectoredbyaphids.

Disease Symptoms:WMV causes leaves to develop mosaic patterns of light yellowand lightgreenpatchesandsometimesring-shapedspotsareproduced.Whenseverelyinfected,leavescanbecrinkled.Fruitmaybedistortedorhavevariations(breaks)insurfacecolor.Fruitmayalsodeveloptumorsandspots.Severelyinfectedplantsmaybestunted.

Control

• Control volunteer cucurbit species in and near the painting that can serve as a source of the virus;

• Sanitation-Removeanddestroyinfectedplantpartsandfruitsinthefieldandin storage. Special care should be given to removing infected fruit during sorting and packing;

• Control aphid vectors that spread the virus with effective insecticides.

Figure 12.5 Symptoms of cucumber mosaic virus. Author: Thomas A. Zitter

Figure 12.6 Symptoms of watermelon mosaci virus. Source: California Agriculture


Melon

DiseasescausedbyBacteriaBacterial Fruit Blotch

Causal agent – Acidovora xavenae. ssp. Citrulli. Bacterial fruit blotch is a veryimportant disease on melon and watermelon. The bacteria can overwinter in melon and watermelon rinds and other plant debris in the field, volunteer melon and watermelon plantsandotherinfectedcucurbits,includingmanyweedspecies.Thebacteriaarealsoseedborneandcommonlyinfecttransplants.Thepathogenmayalsobetransmittedbycontaminatedworkersandequipment.Thediseasedevelopsrapidlyundermoist(wet)and warm conditions. The pathogen is splashed dispersed and infection can occur with leafwetnessperiodsofonly30minutesattemperaturearound26°C.Whenthediseaseissevere,upto80percentofthefruitcanbelost.

DiseaseSymptoms:Acharacteristic symptomofbacterial fruitblotch isadarkorlive green stain or blotch on the upper surface of the fruit. The blotch is first noticeable asasmallwater-soakedarea,lessthan1to2cmindiameter.Latertheblotchesrapidlyexpandtocovermuchofthefruitsurfacewithinsevento10days.Astheblotchesincreaseinsize,theareaaroundtheinitialinfectionsitebecomesnecrotic(dead).Inadvancedstages of disease development, the skin of the rind ruptures and often a transparent or amber-coloredsubstanceisexuded.Colonizationofthefruitbysecondaryorganismsresults in fruit rot and collapse of the entire fruit. The pathogen is seed bore and is commonlytransmittedoninfectedtransplants.Thefirstsymptomsonseedlingsareawater-soakedareaontheundersideofthecotyledons.Asthecotyledonsexpandthelesionsbecomenecrotic. Lesionsalsodeveloponyoung leavesandappearas small,darkbrownareaswithachlorotic(yellow)marginorhalo.

Control


• Practice crop rotation in which cucurbit crops are not planted for at least three years;

• Control volunteer melon and watermelon plants in fields that are being rotated away from melon and watermelon and volunteer plants near establishedplantings;


• Foliarapplicationsofcopperfungicidesasprotectantspraysmaybebeneficial.Copperspraysmustbeinitiatedbeforethediseasebecomeswellestablishedinthe planting.

Angular Leaf Spot

Causal Agent – Pseudomonas syringae. pv. Lachrymans. Angular leaf spot is the most widespread bacterial disease of cucurbits. The bacteria overwinter in infested cropresidues(debris)andcansurviveforuptotwo-and-a-halfyearsindryleaves.Thepathogen is also seed borne and can overwinter in infected seeds. As infected seeds germinate, the young emerging seedlings are infected.The disease first appears onleaves, later infecting fruit and contaminating seed. The bacteria is carried from leaf toleafandplanttoplantbysplashingwaterfromrainorirrigation,byinsects,onthehandsandarmsofpickers,andonfarmmachinery.Thebacteriaentertheplantthroughnaturalopeningsandwoundscausedbyabrasion.Windblownsandy soil containing

Figure 12.8 Symptoms of angular leaf spot. Source: Ministry of Agriculture Barbados

Figure 12.7 Symptoms of bacterial fruit blotch.Author: David B. Langston

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infesteddebrisisveryeffectiveinspreadingthedisease.Withinthecanopy,bacteriaarewashedbywaterfrominfectedleavesontoflowersandfruitwhereadditionalinfectionsoccur.Thediseasecanaffecttheplantatanystageofdevelopment,but isespeciallydamagingduringearlystagesofstagesofplantdevelopment.

DiseaseSymptoms:The disease first appears as small, water–soaked spots on leaves. Thespotsusuallyexpanduntiltheyaredelimitedbylargerveinsintheleaf,whichgivesthem an angular appearance. Under conditions of high relative humidity, a drop ofcleartomilkyexudatesdevelopsonthelowersurfaceoftheleafspots.Theexudatesdrytoformathinwhitecrustonornexttotheleafspot.Onleavesthespotsbecomedry,turntanbrown,andmaydropout.Onhighlysusceptiblecultivars,leafspotsmayhave a yellow halo ormargin. Spots can also develop on petioles, stems and fruits.Thewhite,crustyexudatescanbeobservedonthesespots.Onfruit,spotsaresmall,circularandwater-soaked,1to3mmindiameterandoftenhavealighttancenter.Fruitrotcanpenetratedeeplyintothefruitcausinganinternalrot.Rottedtissuesareoftencolonizedbybacteriacausingasecondarysoftrot.Fruitsinfectedwhentheyareyoungcan become deformed and curved.

Control




• Wherepossible,usefurrowirrigationandavoidoverheadirrigationespeciallyifthe disease is established in the field. Avoid using surface drainage water from near cucurbit fields for irrigation;

• Avoid entering fields for cultivation or harvesting if foliage is wet from rain, dew or irrigation water;

• Select and use resistant varieties when available;

• Foliarapplicationsofcopperfungicidesasprotectantspraysmaybebeneficial.Copperspraysmustbeinitiatedbeforethediseasebecomeswellestablishedinthe planting.

Insects


ThelargemajorityofinsectsbelongtothephylumArthropoda,whichincludestheclassesof Insecta (the insects) andArachnida (themites and the spiders).The listofpestsalsoincludesanumberofrepresentativesofotherphylasuchas:theroundworms(nematodes),mollusks(snails&slugs),andmammals(mouse-likerodents).Thenumberof species of insects on the earth is over a million. These include numerous harmful, beneficialandindifferentinsects.Inthisrespect,Acarina(asubclassoftheArachnida)is significant, withmore than 500,000 species. Among the nematodes, interventionis requiredbyspecialmeasures for rootgallnematode,potatostemnematode,beetnematode, and southern gall nematode.

Alargemajorityoftheabove-listedharmfulorganismsarecapableofbringingoncatastrophic damage and, without implementation of special preventative measures; eventhepossibilityofgrowingspecificnutrientplantsmaybequestioned.However,itshouldalsobenoted,thatamonginsectsandmitestherealsoexistmanybeneficialspecies,whichalsopartlyregulatethenumbersofharmfulinsectsandmitesandoftenplayasignificantroleinmaintainingthebalanceofbiocenosis.

Theinsectbodyconsistsofthreesegments:head,thoraxandabdomen.Theheadcontains one pair of complex faceted eyes and simple eyes, one pair of antennae,andassortedmouthorgansforfeedinginvariouswaysonavarietyofhosts.Theyaremodified for gnawing, puncturing-sucking, sucking, drilling, cutting-sucking, licking,scraping,etc.The thorax is thepointofattachment for thewingsand legs, thuskeyindispersal of these creatures.The thoraxhasonepair of legs for eachof the threethoraxsegments.Theabdomenconsistsof11segments,thoughinafewoftheinsects,thesesegmentsmaybefusedorreducedinsize.Theabdomenalsocontainsmostofthedigestive,respiratory,excretoryandreproductivestructures.Considerablevariationandmanyadoptionsinthebodyofinsectsoccur,especiallywings,legs,antennaeandmouthparts.

Theoutsideoftheinsectbodyiscoveredwithadeadlayercalledthecuticle.Itneitherstretches nor grows and performs as a protective outer coat or skeleton, in addition to manyotherfunctions.Insectsreplacetheircuticleseveraltimesduringtheirlarvalphaseandonceintheirpupalphase.Intheirbodyinsectsaccommodatethefollowingorgansystems:bloodcirculation(theso-calledspinalpipe),fooddigestive(front,middleandback intestines), breathing (tracheas and tracheoles), excretion (malpighian tubules,fattissue),andneural(neuralringandstomachneuralchain),andreproductiveorgans(testiclesandovaries).

Insects reproduce through gender (gamogenetic), genderless (parthenogenesiswithout male participation) and sometimes hetero genetic (gender and genderlessreproduction in turns) reproduction. Their development includes two periods:embryonic and post-embryonic. Embryonic development progresses in ovum andends in formationofa larva,whichexits theovum’scoversandbegins to feed.Withthisbegins thepost-embryonicperiod,whichprogresses throughthevariousstagesofmetamorphosis.Completemetamorphosesaremostcommon.During incompletemetamorphosis,newlyhatchedlarvaeresembletheiradultform,graduallyincreasinginsizeuntiltheyreachtheadultform.SuchtransformationischaracteristicofOrthoptera,Homoptera,Hemiptera,etc.Thisisdrasticallydifferentfromcompletemetamorphosiswhich undergoes four phases of development: egg, larva, pupa, and mature insect (imago). In insectswith completemetamorphosis (Lepidoptera, Coleoptera, Diptera,etc.), a newly hatched larva does not resemble the adult form and undergoes anadditional fourth pupal phase during its development cycle. One full developmentcycle, startingwith theeggphase to the imagocapableofproducingoffspring, is a

Insects

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generation.Duringayear, theyproducevariousgenerationsdependingonthetype,nourishment,hygrothermalconditionsoftheenvironment,andotherecologicalfactors.

Insects andmites are cold-blooded (poikilothermic) organisms, since their bodytemperature depends on the temperature of the environment. For the majority ofinsects, their lower thermal threshold of development is 10°C and the upper is 38°to 40°C, although exceptions do exist. Temperature recorded in natural conditionsabove10°Ciscalledeffectivetemperature.Totalofeffectivetemperaturesisextremelysignificantforreproductionanddevelopmentofspecificharmfultypesingivenregions,aswellasforecastingharmtobeexpectedfromit.

Thesciencewhichstudiesmitesiscalledacarology.Therearemorethanhalfamillionknownspeciesofmites,althoughonlyabout50,000havecurrentlybeenstudied.Theyaresmallanimals.Forexample,tetrapodilianarenotvisibletotheunarmedeye.Miteshavenoprimarysegmentation,althoughtheirbodyissegmented,dividedintodivisions,i.e. tagmasand, in tetranychidmites, is representedby thegnathosoma (comprisingthe mouth and feeding parts) and the idiosoma. Idiosoma includes propodosoma,metapodosoma and opisthosoma. Bristles of various shapes and purposes, located ontheiroutsideshell,formthebody.Mitesundergothefollowingphasesduringtheirdevelopment cycle: egg, larva, protonymph, deutonymph, tritonymph and maturephase.Also,four-leggedmitesomitthelarvalphase,whileeight-leggedmitesdonotundergothetritonymphphase.Larvaeofthelatterhavethreepairsoflegs.Inordertodiminishthedamagecausedbyinsectsandmites,aswellasotherpests(nematodes,mollusks, mouse-like rodents), there exist various control measures: agro-technical,physical, mechanical, genetic, biological, chemical, quarantine, biotechnical andintegrated methods.

Agro-technicalmeasuresimplyallthoseactivities,whichneedtobeundertakenfordevelopment of specific agricultural crops or other plants: soil cultivation, cleaning land plots from weeds and disposing of plant remains, observing the deadlines and rules of sowing and planting, irrigation, etc.

Biological control is a way of reducing the numbers of harmful organisms, byutilizing natural enemies, other living organisms, to assist in their control. The most commonbio-controlagentsarepredators,parasites,andpathogens.Predatorsattackthepreyandsuddenlydestroythem.Parasites,meanwhile,liveinsideorexternallyonthehost’sbodyandfeedonitstissues.Thehostremainsaliveforawhilebutgraduallylosesvitalityandfinallydies.

Thischapterdescribesthemaininsect/mitepestswhichcommonlyattackvegetablecropsinGeorgia,aswellastheircomposition,relationshipwithenvironmentalfactorsand integratedmethods for theirmanagement/control. Attached to the chapter aretableswhichcontainthemainpesticidesusedagainstpestsinGeorgia,alongwiththeirdosages, in addition, each pest is illustrated to aid in recognition.

Mole Cricket(Gryllotalpidae)

Description:Thebodylengthofanadultmolecricketrangesfrom35to50mm.Thefrontfootoftheinsectiscoveredwithfourfinger-liketeeth,whilebackfeethavefourorfiveclaws,withalmostequaldistancebetweenthem.Foundationofthebackpartofthefemale cricket is almost parallel, vertical dark brown veins are found on the upper wings.

Figure 13.1 Picture of mole cricket. Source: Wikipedia

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Insects

Mole crickets are light brown insects whose front legs are large and resemble small shovels.Molecricketstunnelunderthesoilandfeedonplantroots.Theyalsodisruptanddislodgeplantsby theirdigging.Likecutworms,molecricketsareactiveonlyatnight andhide in their tunnelsduring theday.The tunnels areapproximately1 cm.in diameter and the soil surface appears loosened and raised as if a miniature mole (amammal)hadtunneled.Molecricketswinterinthesoil,mainlyasolderlarvaeandadults,atdifferentdepths.Thispestthrivesinrichsoils,especiallythosebeingfertilizedwith organic fertilizers.

Overwinteredindividualsbeginlayingeggsaftercompletinggrowthandbecomingsexually mature, which lasts until August. Overwintering adults, meanwhile, beginlaying eggs after additional nutrition and sexualmaturation.This process lasts fromApril until June.Thepestprefershumus-rich soils for egg laying. Its eggproductionreaches200-300eggsperfemale.Molecricketsplacetheireggsinthenestitmakesinadvance.Durationofembryonicdevelopmentlastsuptothreeweeks.

Newlyhatchedlarvaelivetogetherfor3to4weeksandthendisperse.Molecricketslikehumidity,droughtinthesoilforcesthemtomovetomoisterareasandiftheyfailtofindamoistenvironmentnearby,theydie.Theycanswimwell,whichcontributestotheirabilitytodisperserapidly.

InGeorgia,thispestcompletesitsdevelopmentallifecycleinoneyear.

Negative economic significance: Mole crickets damage tomato, potato and other vegetablecrops,onsandyandespeciallyclaysoils.Itgnawsrootsandstems,quiteoftendestroying25percentoftheseedlings.Tracesofthispestareeasilynoticeableonthesoil surface.

Control measures

• Maketrapsandplacethemontheinfestedareainthespring,orsevento10daysbefore transplanting seedlingsor sowing seed-material.This samemeasure isalsoeffectiveonclaysoils.Oneofthemethodsofmakingatrapisasfollows:startwith20gramsofchlorpyrifos(Dursban)insecticide,addoneliterofwaterthanmixinfivekgofwheatbranandadd200gramsofoil.Aftermixingthisproductscatteredoveranareaofapproximately100squaremeters.

Wireworms(larvae) ClickBeetles(adults)

Description:Mostwirewormlarvaearehard,chestnutbrown,smooth,varyingfrom10to30mminlengthwhenfullygrown.Somespeciesaresoft,andwhiteoryellowishincolor.Eveninsmallnumbers(onetotwospecimensper1m²)theycansignificantlydamage tomato crops. Chances of them spreading are increased in cases where the tomatoes are grown near uncultivated land. Click beetles have a three to four yeardevelopmentcycle.

Negative economic significance: Wirewormlarvaedamagerootsystemsofpotato,beet,carrot, tomatoandothervegetablecrops.Theypenetrate thestalk,gnawon itandmovethroughitinvariousdirections.Damagedplantsbreak.Larvaearecapableofmovingontootherundamagedplants.Intheholeswhichappearasaresultofinsectactivity,micro-organismsdevelop,causingrot.

Figure 13.2 Picture of click beetles. Source: Corn Insect and Disease Guide

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Cropsattackedbywirewormshavereducedplantpopulations,sincetheyfeedontheseedspriortogerminationorjustaftergermination.Theplantstandmaycontinueto deteriorate, because wireworms bore into underground portions of the stem, causing plants towitheranddie.Theycontinueto feeduponthesmall rootsofmanyplantsthroughout the season.

Control measures

• Timelycultivationofsoilforweeddestructionpurposesisrecommended;plantnutrition with chemicals containing nitrogen also helps in insect management;

• Timely and high-quality appropriate chemical treatments are recommendedto manage this pest, such as thiamethoxam, carbosulfan, ethoprophos andimidacloprid.

Nematodes(Roundworms)

Nematodes are among the most dangerous pests of vegetable crops. Two of the most notable are the root-knot nematode (Meloidogy nemarioni) and potato rotnematode(Ditylenchusdestructor).

Description:Nematodesaresmall(1-5mm)circularworms,whichpenetrateplantroot hairs and then root branches.

Negative economic significance: Nematodes damage beet, potato and several other vegetable crops. Bulging spots of various shapes appear in areas of damage. As a result ofdamage,plantnutritionregimeisdisrupted,whichisfollowedbyitsdeath.Damageissignificantlyincreasedbyhot,sunnyweather.

Prevention: Inordertomitigatethespreadingofnematodes,itisfirstofallnecessarytoobservethemeasuresenvisagedbyquarantinelegislation:itisinadmissibletouseseedlings from contaminated zones, where nematodes have been discovered. Water flowingnearaffectedlandcannotbeused.Itisnecessarytoplacedisinfectingmatsingreenhouseentrances,aswellastodisinfectequipment.Measuresagainstspreadingof nematodes include soil mulching with straw or sawdust, because that weakens the effect of heat and draught and strengthens the plant, which, in its turn, predetermines increaseof theplant’s resistance topests.Whennematodesareencountered in claysoils,itisnecessarytosterilizeorfumigatethesoil.Effectivechemicalswithgoodresultsincludenematicidessuchasethoprophos,oxamylandmetam-sodium.

Root Knot Nematode (Meloidogynemarioni)

Description:Thelengthofthematuremalerangesfrom1.2to1.9mm,andthewidthrangesfrom0.3to0.36mm.Thebodyofthenematodeissomewhattaperedfromthefront to the broader tail end. Females are white in color; the length of mature nematodes isupto1mm,thewidthisupto0.5mm.Theirbodyisroundedattheendandhastwogendertubes,eachofthemwithstronglydevelopedovaries.

Figure 13.3 Root-knot nematode. Source: Edible San Marcos

Insects


Negative economic significance: Among vegetable crops, this pest significantlydamages watermelon, cantaloupe, cucumber, beet, carrot, potato and eggplant. Apart fromthis,itdamagesover1,500speciesofplants.Itslarvaepenetratethetipsofgrowingroots of nutritious plants, get to their center, and begin feeding. As a result, the root’s parenchymabegins togrowthroughrapidandmultiplecelldivisionsandsurroundsthe larva causing galls, which cause the plants to decline.

Control measures

• healthyseedandplantingmaterials.

• timelyandhigh-qualityappropriatesprays.

Potato Rot Nematode(Ditylenchusdestructor)

Description:Thebody lengthofmaturemalenematoderanges from0.72 to1.35mm,while thewidth ranges from0.02to 0.025mm.Themature female has asimilarlength.However,shecanbealittlewider.Thebodyofthenematodesiscoveredwithhard and transparent cuticle. Bodies of both females andmales are thread-shaped.Their bodies are narrowed at the ends, the head part is obtuse. This pest survives low temperaturewithoutdamage.Thelowerthermalmarginofitsembryonicdevelopmentis5°C,whilethatofpost-embryonicdevelopmentis3°C.Thispestisalsoabletotoleratehigh temperatures (50°C.overaperiodof fourhours).During itsdevelopmentcycle,potato root nematode undergoes egg, larva and mature stages. The developmental cyclelastsfor20to25days;duringthattimelarvaeundergofivestages.Inwinteritcanbe encountered in all stages.

Economic significance: This pest damages potato both in the field and in storage. Damagedtuberskinsturngreyandleatheryindamagedareas.Theseareasaresunken,whiletheskincracks,whichdistinguishesitradicallyfromhealthyareas.

Itshouldbenotedthatinthefielditdamagesthepotatostemsandfoliage,alongwiththetubers.Importantnote:Potatorootnematodedamagestheearlyandmediumvarietiesofpotatomostintensely.

Control measures

• Selecthealthyplantingmaterial;

• Croprotation-Itisnotrecommendedtoproducepotatoforfourtofiveyearsonthe same land, where this pest is present;

• Weed control is important;

• Utilizetimelyandhigh-qualitychemicaltreatments.

Colorado Potato Beetle(Leptinotarsadecemlineata)

Description: The larva of the Colorado potato beetle is about 15 to 16 mm inlength. Its head, front sideofback and legs areblack.young larvae are reddishororangeincolor;maturelarvaeareorangewithshadesofyellow.Middlesegmentsofthelarvaabdomenareextremelywideandbulgingandarelinedonthesideswithtwolongitudinalrowsofblackdots.Thebeetlebodyrangesupto15mminlength.

Figure 13.5 Picture of Colorado potato beetle. Source: Wikipedia

Figure 13.4 Symptoms of potato rot nematode infected potatoe. Source:The Global Potato Industry

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Adultantennaehave12segments,frombelowtheyareyellowandontoptheyareblack.Ithaselevenspotsofvariousshapesandsizesonitsfrontsideofbackandatriangularspotonitsforehead.Wingsareyellowincolor,onwhichlongitudinalblackstripes canbe clearly seen.Thepestoverwinters in the soil as anadult.Thedepthdependsonagro-environmentalfeaturesofthelocation.Beetleoverwinteringtakesplacewhen temperature in the layer,where thepest is, reaches14°C+.During thisperiod, beetles require additional nutrition, forwhich they feed on leaves of bothpotatoandotherplantsinthefamily

Solanaceae(tomato,eggplant,pepper,etc).Afteradditionalnutrition,beetlesbeginto lay eggson thebottom sideof foliageof theplants representing the solanaceaefamily. Eggs are laid in clusters, each containing several dozen. Egg-laying processprogressesmostintenselywhentemperatureexceeds17°C+.Aftergrowthiscompletethe larvaedescendandpupate in thesoil. In theconditionsofGeorgia there twotothreegenerationsofColoradopotatobeetleperyear.

Negative economic significance: Mature larvae of the Colorado potato beetle causesignificantdamagebyfeedingonleavesandstemsoftomato,potato,pepper,eggplantandothercropsrepresentingthefamilysolanaceae.Asfewas25larvaecandestroyupto50percentoftheplant’sfoliage,whichrapidlydiminishesproductivityof the plant.

Control measures

• Conduct fall plowing in the spring;

• Inorder foroverwinteredbeetlesnot to spreadon large territory,arrangingatrapplotcanbeeffective,theareaofwhichisdeterminedaccordingtonecessityandmayconstitute200-5000m2.Onsuchplotstheyplantearlypotato,whichattractsoverwinteredbeetlesanditthenbecomeseasiertoeradicatethembychemical or other means;

• During chemical spraying against the Colorado beetle, it is recommendedto use insecticides such ascypermethrin, thiamethoxam, pirimiphos-methyl,acetamiprid,dimethoate,deltamethrinandchlorpyrifos.

Aphids

The Melon aphid (Myzuspersicae), beet aphid (Aphis fabae) and cabbage aphid(Brevicoryne brassicae) are the aphids which inflict themost damage on vegetablecrops inGeorgia.Aphids are small, pear-shapedpestswhich live in colonies.Aphidsmultiplybylayingeggsor,inhotclimateareas,theyoftenreproducewithoutcoupling.Aphidscanmovefromplanttoplantorleaftoleafbothinthewinglessnymphstageand in the winged or wingless imago stages. After settling on a plant, aphids feed on leaves.Theirexistencecausesconsiderabledamagetocrops.Aphidstransmitvariousdiseases; provoke leaf spot, chlorosis, as well as leaf curl, deformation and blossom drop. Thenumberofvirusesspreadbyaphidssignificantlyexceedsthenumbersofvirusesspread by other pests. These include cucumbermosaic virus, tobaccomosaic virus,alfalfa mosaic virus and others.

Control measures

• Destroyplantremains;

• Timingofappropriatechemicaltreatmentsisveryimportant;

Insects

Figure 13.7 Picture of black bean aphid. Source: Wikipedia


• In case of necessity of undertaking chemical measures against aphids onvegetable crops, the following products have been utilized successfully:cypermethrin, alpha-cypermethrin, thiamethoxam, pirimiphos-methyl,dimethoate, deltamethrin, chlorpyrifos, bifenthrin, thiacloprid, lambda-cyhalothrin,methomyl,andmalathion.

Melon Aphid(Aphisgossypii)

Description:Mature melon aphids can be both winged and wingless. Winged aphids have transparentwings, as well as antennae (moustaches), black heads and thorax.Antennaeofwinglessfemalesarepaleyellowincolorwithsixsegments.Thefirstandsecond are brown, while the one at the tip is black. Cornicles, head, middle and rear part ofbackarealsoblack.Theyhaveblackspotsontheabdomen.Theaphid’sbodyisoval-shapedwiththelengthof1.2to2.1mm.Larvaeareinitiallypalegreenandlaterturnyellowish-greenincolor.

This pestmostly overwinters onweeds, in the imago stage, although it can alsooverwinterasanymph.Inspring,whenairtemperaturereaches12°C,aphidsbegintoreproduceandfeed.Theyinitiallyfeedonweedfoliageandthenmovetoagriculturalcrops.

Negative economic significance: Insandysoils,aphidsmovetocucumber inJuly-August,whileonclaysoilsthishappensearlierinspring.Aphidcoloniessettleonbottomsides of cucumber leaves, in side vegetative branches and on knots in the blossoms. Theysuckoutjuicesandcausetheirdeformation.Fungalpowdersometimesdevelopsonleafsurface,asaresultofaphidactivity.

Control measures



• Timelyandhigh-qualityappropriatechemicaltreatmentisusuallyneeded.

Black Bean Aphid(Aphisfabae)

Description:Wingedblackbeanaphidsareglossydarkgreenorbrownish-blackincolor.Winglessaphidsareblack,withaslightlygreenorbrowncoloring.Nymphshave dark maroon wing-rudiments, as well as clearly visible small white dots onabdominalsegments.Legsaregreenishoryellowishgrey,withdarkanklesandthightips.Cornicles(sap-tubes)arelongerthanthetail.Backanklesofegg-layingfemalesarethickened,ascomparedtomales;theyarewinged,withnarrow,straight-angledbodies.

Negative economic significance: This pest causes significant damage to beet crops. Itlivesonthebottomsideofthecropleaf;itsucksontheleaves,damagingtheirveinsandcausingthemtobecomedeformedandcurlup.Aphidsespeciallydamageseedbeetplantings,theirstalksandflowers,causingstuntedgrowthanddiminishedseedproduction.

Figure 13.6 Picture ofaphis gossypii. Source: Gestión Integrada de Plagas y Enfermedades en Cítricos

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Figure 13.9 Picture of red cabbage bug. Author: Luis Fernandez Garcia

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Control measures


• Utilizetimelyandhigh-qualityappropriatechemicaltreatments.

Cabbage Aphid(Brevicorynebrassicae)

Description: The body length of this wingless parthenogenesis aphid rangesfrom1.8to2.4mm.It iscoveredwithwhitish-waxydust.Widervarietiesdonothavesecondaryrhyniales,whilewingedoneshavethemonlyonthethirdandsometimesfourthsegmentoftheantennae(moustaches).Lengthofthecornice(sap-tube)twiceexceedsitswidth,whileitscolorisdarkbrown.Aphidsarelightgreen,withblackheadsandhavesixsegmentedantennae.Thelengthofthewingedviviparousfemaleis1.5to2mm,whileherfrontwingsare1.5timeslongerthanherbody.Antennaearealmostaslongasthebody.Bodyandchestaredarkbrown,whiletheabdomenisyellowish-greenandcoveredwithwaxydust.Lengthofgamogeneticfemalesisupto0.8to1.7mm.Theyarenotcoveredwithwaxydust.Tarsioftheirhindlegsareenlarged.Maleslook similar to winged females and have across dark stripes on the dorsal side of their abdomen.Headandthoraxareshinyblack.Cabbageaphid’seggsareovalinshapeandassumeashinyblackcolorintheprocessofembryodevelopment.

Negative economic significance: The cabbage aphid severely damagesrepresentatives of Cruciferous vegetables, especially cabbage. Leaves inhabited bypestcoloniesaredamagedandfailtoperformtheirfunctions.Insuchcases,leavesaretwistedandmisshapen,plantgrowthissloweddown,andseedslooseproductivity.

Control measures

• Weedcontrolisquiteimportant;

• Collectinganddestroyingplantremainsdelaysandreducesaphidattack;

• Timelyandhigh-qualityappropriatechemicaltreatmentiswarranted.

Red Cabbage Bug(EurydemaOrnatum)

Description:Thenymphinitsmaturestage(lastinstar)isupto4mminlength.Itshead isgrayish-brown;thebody isblackandcoveredwithsmallwarts.However, theadultis7.8to

8.5mmlong.Ithassixblackspotsonthefrontsideofitsthorax.Theouteredgeofupperwingsisred,yellowish-whiteorwhite,withblackspotsinthecenter.Thethoraxisredonthebottom,sometimeswithoneorseveralspots.Ithasasuckingmouthparts.

Negative economic significance: This pest significantly damages cabbage.Whilefeeding,itpiercesleaftissueswithitsproboscis(trunk)andsucksthejuice.Piercedareasofcabbageleavesdevelophardenedyellowspots.Redcabbagebugfeedingactivitiescausetheleavestodie.Cabbage,damagedbythispest,can’tformaheadandintheseed plots, lose their blossoms.

Figure 13.8 Cabbage aphids on curly kale. Author: Rasbak

Insects

Figure 13.11 Picture of bulb mite. Source: Macroid


Control measures

• Collectanddestroyplantremains;• Fall plowing is recommended;• Use timely and high-quality appropriate chemical treatment. In this case,

effectiveresultsinvegetablecropsarebroughtbyuseofselectiveinsecticidessuchascypermethrin,dimethoate,deltamethrinandfenitrothion.

Mites

The most severe damage to vegetable crops is caused by the carmine mites (Tetranychustelarius),thedrybulbmite(Aceriatulipae),thebulbmite(Rhizoglyphusechimopus), the red spider mite (Tetranychus urticae) and the tomato russet mites(Vasateslycopersici).Itshouldbenotedthatasarule,mitesinflictmostdamageunderdrought conditions. Mites must be eradicated before bloom begins.

Control measures


• Disinfectgreenhouses;

• When undertaking chemical measures against mites on vegetable crops, effective resultsarebroughtbyuseof selectiveacaricides suchaspyrimiphos-methylanddimethoate.

Carmine Mite(Tetranychustelarius)

Description:Insummer,thispestisgreenish,yelloworbrown,whilefromautumnto spring it is reddish or dark orange. Male mites are smaller than females. The Carmine Mite has large dark spots on the sides and also prominent bristles on the back.

Negative economic significance: The carmine mite damages green parts of the crops andcausesphysiologicalchanges.Waterevaporationprocessoftheplantintensifiesatthepointofpiercing.Consistencyofdamagedleaveschanges,duetolossofmoistureandtheybecomethin.Suchchangesnegativelyaffectnotjustviabilityoftheplant,butalsoquantitativeandqualitativeparametersoftheharvestedcrop.Pestactivitiesareexpectedtoresultinradicalweakeningordeathoftheplantandpoorvegetablequality.

Control measures

• Destroyplantremains;• Disinfectinggreenhouses;• Timelyapplicationofinsecticideiscritical,asistheuseofhigh-qualityappropriate

chemical treatment. DryBulbMite(Aceriatulipae)

Description:Aceriaisagenusofmitesbelongingtothefamilyeriophyidae (the gall mites).Thesetinyanimalsareparasitesofplants.Severalspeciescancauseblisteringandgalls,includingerineumgalls.Afewareeconomicallysignificantpests,whileothers

Figure 13.10 Picture of carmine mite. Source: TurbosQuid

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Figure 13.12 Picture of bulb mite. Source: Macroid

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areusefulasagentsofbiologicalpestcontrolofinvasiveplants.Bodylengthofamaturemiteisapproximately0.2mm.Itiscolorlessandhastwopairsoflegs,directedtowardsthefrontofthebody.

Negative economic significance: This pest severely damages garlic. Damageis especiallynoticeable in the caseof spreadingof themite in storage.Garlicbulbs,damagedbythedrybulbmitedryduringthesecondhalfofwinter,becomeunfitforuseinspring.Inspring,mitesfindthemselvesinthefield,alongwithgarliccloves.Alongwithplantgrowth,thepestmovesontothebrushes,asaresultofwhichtheyyellow,dry,anddie.Inonions,thepestislocatedonthebottomofbrushes,whileongarlicandleekitismostlylocatedinleaffolds,alongthemainvein.

Control measures

• Destroyplantresidues;


• Timelyandhigh-qualityappropriatechemicaltreatmentsareimperative.

Bulb Mite(Rhizoglyphusechinopus)

Description: Adult -Maturebulbmitesvaryfrom0.5to1.1mmlongandhavefourpairs of legs.Their bodies are shiny,white, somewhat transparent, and smoothwithreddish brown appendages.

Egg-Theeggiswhiteandtranslucent,0.12mmlong,andellipsoidal.

Larva-Fullydevelopedlarvaeare0.25mmlong.Whiteandoval,larvaehaveonlythree pairs of legs and lack genital suckers.

Protonymph -Theprotonymphhasfourpairsoflegs;itisovalandapproximately0.4mmlong.Thisstagecanbedistinguishedfromthetritonymphbyhavingtwogenitalsuckers,whereasthetritonymphhasthreeorfoursuckers.

Deutonymph -Thisquiescentstageisoval,convexontop,flattenedbelow,brown,and0.2to0.3mmlong.Themouthpansareabsent.Onthebacklowersideisaconspicuoussucker plate.

Tritonymph -Thetritonymphisabout0.5mminlengthandhasnotyetdevelopedadistinct genital aperture.

Damage:The bulb mite damages the bottom of onion and garlic bulbs, as a result of whichtheybecomeeasilyseparatedfromthebulb.Duringtheintensivereproductionperiod, the pest invades the bulb, settles and feeds there as a result. The bulb begins to rot;arottenbulbismoreattractivetopests,duetoitsbeinghygrophilous.

Itisveryimportanttoavoidroughhandlingofbulbstopreventinjurythatwouldallow bulb mites to obtain access.

Control measures

• Destroyplantresidues;


• Timelyandhigh-qualityappropriatechemicaltreatment.

Insects

Figure 13.14 Tomato (and hemp) russet mite. Source: Everwood Farm

Figure 13.13 Picture of red spider mite. Source: Pro Gilles San Martin

Figure 13.15 Picture of greenhouse whitefly. Source: Weiße Fliege


Red Spider Mite(Tetranychusurticae)

Description: The mite’s body is oval-shaped and greenish-yellow in color. Theoverwintering process begins in August and lasts until October. It overwinters ingreenhouse corners and plant remains in the soil. In spring, the pest abandons itsoverwinteringplaceandsettlesonweeds.Intemperaturesof12°to13°C,pestsbegintolayeggsonbottomsidesofweedandvegetablecropleaves.Afterfivetosevendays,larvae hatch, which are similar to mature mites. Apart from cucumber, red spider mites damagewatermelon,cantaloupe,tomato,andmanyotheragriculturalcrops.Thispestisespeciallydangerousonclaysoil.Damageisespeciallysevereindroughtperiodsandhot weather.

Economic importance: Mites live and feed on bottom sides of foliage. When feeding, theysuckcell juice fromthe leaves. Initially, light-coloreddotsdevelopondamagedleaves.Lateron,discoloredareasdevelopontheleaves,asaresulttheydry.Asaresultof mites feeding, blossoms, knots and fruit fall off the plants.

Control measures

• Clean greenhouses and remove plant remains from surrounding areas;

• Use weed control on open soil and near greenhouses.

• Removeanddestroydamagedleaves.

• Timelyapplicationofhigh-qualityacaricidesisnecessary.

Tomato Russet Mite(Vasateslycopersici)

Description:Thispestisadark-rust-colored,verysmall,four-leggedmite.Itispaleyellowandonlyturnsrust-coloredbeforelayingeggs.Itsbodynarrowsfromthethoraxtowards the abdomen, which is divided into rings, with lateral grooves. The last two ringsof theabdomencarrytwothreadlikeaddenda, the lengthofwhichequalsonethirdofthebody’slength.

Economic significance: Larvae andmature pests inflict significant damage uponagricultural crops and wild plants representing the Solanaceous plants. Pests gather intocoloniesonplantleavesandfruit,bothonsandandclaysoils.Leavesandstalksofdamagedplantsassumeabronzecoloringandthendry.Fruitskincoarsens,cracks,andbecomesdark-rustycolored.

Control measures


• Effective results can be achieved through use of acaricides and insecto-acaricidessuchaslambda-cyhalothrin,malathion,deltamethrinandspiromesifen.

GreenhouseWhitefly(Trialeurodesvaporariorum)

Description:The greenhousewhitefly is a small, white, insectwhich flies aroundquickly.Thiswhiteflyinhabitsthetemperateregionsoftheworld.Itisaprimaryinsect

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pest of many vegetables crops, frequently being found in glasshouses and otherprotectedhorticulturalenvironments.Adultsare1to2mmin length,withyellowishbodiesandwax-coatedwings.Thewingsareheldnearlyparalleltotheleafsurface.

Economic significance: Thewhiteflydamagesallkindsofplantsonclaysoilandinsomecasesalsodamagesvegetablecropsonsandysoil.Itsignificantlydamagestomatoon clay soil, since this pest has several generations during one season. The femalewhiteflyliesfrom50to250eggsonthebottomsideofyoungleaves.Theegg-layingprocesslastsforaverylongtime;thus,duringalmostalloftheplant’svegetation,inthegreenhousetherearebothmatureformsofthepestanditslarvae,whichsignificantlycomplicate control of the pest. Existence of a large number of larvae significantlyweakens the plant.

Control measures

• Observe sanitary rules in thegreenhouse: limitoutsideaccess, regularly cleanweeds and plant remains, and disinfect entrance mats;

• Among chemical preparations used against pests on vegetable crops, effective results are brought by insecticides such as: pyriproxyfen, cypermethrin,thiamethoxam,pirimiphos-methyl,acetamiprid,imidaclopridandmalathion;

• If seedbeds or hotbeds are planted outside, whiteflies can be excluded bycovering them with tobacco cloth or screen wire. This candelay theonset ofwhiteflyinfestationsbyseveraldays,oftenlongenoughtoharvesttomatoes.

Thrips

Vegetable crops in Georgia are damaged by various types of thrips, the mostdangerouspestofwhichistheonionthrips(Thripstabaci),whichiscommonalloverthe world. As a rule, thrips reproduce without coupling. Larvae are less mobile; however, maturepestshavewingsandmovealot.Infact,adultsaresolightthattheycanbeblowngreatdistanceswithonlyabreeze.Thelifespanoftheaveragethripsisapproximately20days.Thripsfeedonyoungleavesanddevelopingflowers.Asaresult,leavesfailtodevelop and their curling and deformation begins. Thrips make nests for their eggs on the fruit, and then the feeding of larvae cause development of wounds on fruit. Fruit losescolorandmarketablequality.Althoughitisdifficulttonoticethripsonplants,theycanbeseenasaresultofshakingyoungleavesandflowersontowhitepapersheets.Certaintypesofthripsarealsocapableofspreadingviruses(Tospoviruses).

Control measures

A. Cultural Control

• Crop rotation;

• Destructionofplantremains;

• Deepploughing(25-27cm);

B. Chemical Control

• Among chemical preparations used against thrips on vegetable crops, effective results are brought by insecticides such aspyriproxyfen, cypermethrin,pirimiphos-methyl,thiamethoxamanddimethoate.

Insects

Figure 13.17 Picture of crucifer flea beetles. Source: Field Crop News


OnionThrips(Thripstabaci)

Description:Onion thripsarecosmopolitan insects that feedonawidevarietyofvegetableplants, smallgrains,fieldcrops,andweeds.Theyarean importantpestofcabbage, cauliflower, and onions. This thrips is a small, yellow insect with a lengthof0.8to0.9mm.Ithasnarrowwingsandaflattenedbody.Onefemalecanlay50to60small (length-0.2-1.25mm),whitish-coloredeggs.Eggsaredeposited intotissueofhostplantson thebottomsideof the leaf.Wingless, initiallywhitish-colored, andthen greenish-yellow larvae hatch from eggs. Nymphs are yellow in color and haverudimentarywings.Theyoverwinterinplantremainsinuppersoillayers.InconditionsofGeorgia,thispestcanproducefromsixtosevengenerationsperyear.

Economic importance:Thrips feedbypiercingsurfacetissuesandsuckinguptheexuded plant juices. On onions with continuing leaf growth, these feeding pointselongatetogivethetypicalonionthripssymptoms-whitishspotsandstreaksontheleaves. Intensive feeding results in a silvery-white stippled appearance, sometimesreferred to as white blast or silver top.

Control measures

• Crop rotation assists in thrips management;

• Destroyingweedsandplantremainsreducespestload;

• Ploughingsoilatthedepthof25-27cmreducesthenumberofsurvivors;

• Timelyandhigh-qualityappropriatechemicaltreatmentsareoftennecessary;

• Culturalcontrolsareimportant.Ifpossible,avoidplantingcabbage,cauliflower,oronionsclosetoandimmediatelydownwindofsmallgrainsoralfalfa.

Flea beetles in crucifer crops

Description:Fleabeetlesaresmall(2-3mm),jumpinginsects.Theirmostdangerousrepresentative is the crucifer flea beetle (Phyllotret acruciferae). This pest’s imago ismetallicgreenorblueincolor,itsupperwings,head,andbackarebluish-green,anditslegsareblack.Itsupperwingsaresometimeslinedwithyellow.Larvaehaveabrownishcolor;theirheadsandthelastsegmentsoftheabdomenareyellowish.Thispestlayseggs in theupper layersofsoil,andembryonicdevelopment lasts foraboutaweek.Newlyhatchedlarvaefeedonrootsofcruciferousvegetablesfortwotothreeweeks.Theythengointopupalstageinthesoilincradlesmadeofearth.Pestoverwintersatimago stage, in earth crevices, under plant remains and fallen leaves. The pest comes out ofthewinteringstateattheendofMarchandthebeginningofApril.Theyinitiallysettleonplantsrepresentingthecruciferousfamilyandbeginadditionalfeeding.Fleabeetleactivityanddamagecausedbythemincreasesrapidlyinhot,dryweatherconditions,whendaytemperaturereaches20°Candabove.

Economic significance: Oncabbage,thispestgnawsthetissueonbothsidesoftheleaves;asaresultleavesseemtodevelopulcers.Activitiesoffleabeetlesincruciferouscrops are especiallydamaging tonewlyplanted seedlings. Beetlesmaydamage thegrowthpoint,whichisfollowedbythecollapseoftheseedling.

Control measures

• Removeanddestroyplantremains;

Figure 13.16 Picture of onion thrips. Source: Center for Insect Bioinformatics

Insects

Figure 13.18 Picture of turnip sawfly. Source: NatureSpot

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• Among chemical preparations used against flea beetle son vegetable crops,effectiveresultsarebroughtby insecticidessuchascypermethrin,dimethoate,deltamethrin, lambda-cyhalothrin,phosalone, chlorpyrifos and chlorpyrifos-methyl.

Description:Theimagolengthmeasuresapproximately1.8to2.4mm.Its legsareblack,and itsupperwings,backandheadareashinygreenish-blue.The larvalheadand last segment of the abdomen are a yellowish color. It has dark jaws and three-segmentedantennae(mustaches).Whenmature, itscolor iswhitish. Ithasyellowish-brownhairsonthebody,whileitseggsareoval-oblongshaped.

Economic significance: Pest beetles damage cabbage, turnip, and other vegetable crops.Thispestmostlydamagesleaves.Incaseofmassivereproductionitcompletelydevourstheplant,especiallyyoungplants.It ischaracteristicofthepestthatitfirstofalldestroysyoungpartsoftheplant.Thebeetlealsodamagesflowers,stemsandstalks.

Control measures


• Timely and high-quality chemical treatments should be considered wherethisfleabeetleispresentinlargenumbers;

• RecentstudiesinthemanagementofthecruciferfleabeetleonCanolainNorthAmerica indicate thatdeltamethrinandbifenthrinwerecommonlyused foliarspraysforcontrolofthispestoncanola.Theyalsocomparedsomebiopesticides,includinganematode(Steinernemacarpocapsae),andtwoentomopathogenicfungi(BeauveriabassianaandMetarhiziumbrunneum).Theseresearcherswereoptimisticabouttheuseofbiopesticides,sayingthattheylookedpromising.

TurnipSawfly(Athaliacolibri)

Description:Thelengthofthematurelarvaofthesawflyisapproximately2.0cm.Larvaeareofcylindricalshapeandhavemanywrinklesaroundthebody.Ithasablackhead,threepairsofthoraciclegsandeightpairsoffalselegs.Ithasthreevertical,paralleldarkstripesontheback. Itcanbeeitherblackish-greyorgreenish-grey incolor.Thelengthofthepests’cocoonis8-10mm.Itsinsideissilver-coloredandconsistsofpurethreads,whiletheoutsideiscoveredwithearthparticles.Thepupaisyellow,withthelengthofapproximately7mm.Theadultsawfly’sbackisreddish-yellow.Thehead,frontedgeoftheupperwings,andantennaeareblack,andthelegsareyellow.Bodylengthrangesfrom7to8mm.

Economic significance: The turnip sawfly damages cabbage, turnip, and othervegetable plants. This pest causes especially grave damage to the cabbage crop initsseedlingstage.Theadultsfeedontheflowernectarofumbelliferaeandcruciferaecrops,andlayeggsonthebottomsideof leavesofthesecrops.Atthepointswhereeggsarelaidtheleafbulgesandbecomesdeformedandshiny.

Control measures


• Fall plowing reduces pest pressure;

Insects

Figure 13.20 Picture of cabbage butterfly. Source: Wikimedia Commons

Figure 13.19 Picture of diamondback moth. Source: Wikimedia Commons


• Among chemical preparationsused against turnip sawflyon vegetable crops,effectiveresultsarebroughtaboutbyinsecticidesbasedonpirimiphos-methyland deltamethrin.

DiamondbackMoth(Plutellamaculipennis)

Description:Diamondbackmothlarvaeareabout10to12mmlong.Itsbodyislightgreen, spindle-shaped and coveredwith short, black fur.The head is yellowish darkbrownandhasmanyyellowishspots.Thewingspreadoftheimagois16-17mm.Thefrontnarrowwingsaremostlygrayishontop,withaverticalyellowishorwhitishstripeinthemiddle.Backwingsareshinyandash-colored.Thispestoverwintersinitspupalstage in cabbage and other plant remains. In spring (April orMay), sexuallymaturemothsexitfrompupaeandcopulateandbegintolayeggsonthebottomsidesofplantleaves. Eggsare laid in small clusters along the leaf veins.After three to sevendays,larvaehatchfromeggs,andanewcycleisbegun.

Economic significance: Newlyhatched larvaepenetrate the leafpulp, gnawon itandgeneratewindingtunnels.Afterseveraldays,larvaemovefromthetunnelstotheleaf surface and begin boring roundish and irregular holes in it. This pest causes great damageindroughtandhotyears.Cabbagecropharvestdiminishessignificantlyasaresult of their feeding activities.

Control measures


• Among chemical preparations used against diamondback moth on vegetable crops,effectiveresultsarebroughtbyinsecticidessuchaslambda-cyhalothrin,malathion, esfenvalerate, acetamiprid and malathion.

CabbageWhite(CabbageButterfly)(Pierisbrassicae)

Description:Thematurelarvaofthecabbagewhitebutterflyisyellowish-greenish,withblackdots andyellow stripeson theback and sides anda largewhite spotonthe forehead. The pupa is yellowish-greenish or bluish-greenish, with black bulgesandspotswithanangularbody.Thebutterflyislarge;reachingawingspanof60mm.Femalebutterfliesarelargerthanmales.Themalehaslargethinneedle-likeantennaeandwhitewings.Femalebutterflieshavetwoblackspotsonthebottomsectionoftheirfront wings with round spots on the top wing. Tips of the front wings are characterized withblack,wide,sickle-likespots.

Frontwingsofmalebutterfliesaremonochrome,withoutaspotonthewingtop.Theyonlyhavetwospotsonfrontwingbottomsectionsandsickle-shapedspotsonfrontwingtips.Thecabbagewhitebutterfliesoverwinterinthepupalstage.Itgoesintopupalstageeverywhere-onplants,fences,inbuildings,inplantremain,etc.

In spring, from the month of March, butterflies begin to exit from the pupae.This process lasts until themiddle of May. Butterflies newly exited from the pupaeare sexually immatureandneedadditionalnourishment.They feedon thenectarofcruciferousplants.Asaresultofadditionalnourishment,butterfliesbeginbreedingandafterthreetofourdaysbeginlayingeggs.Thispestlayseggsmostlyonthebottomside

Insects

Figure 13.21 Picture of cabbage moth. Author: Olaf Lenninger

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ofcabbage leaves.Eggsare laid inclusters,eachofwhichaccommodatesup to100eggs.Onebutterflyiscapableoflayingupto300eggs.

Inconditionsoftemperaturesof140or150C,thedurationofembryonicdevelopmentisapproximately10days,whileincoolerconditionsof100to110C,itisabout19days.younglarvaemoveincoloniesandthengraduallyseparate.

Negative economic significance: Thedamageinflictedbythispestuponagricultureisextremelygrave.Newlyhatchedlarvaefeedonthechorionoftheegg,whilematureonesfeedonleafpulp.Asaresultofdamage,onlythemainveinsofleavesremain.Thecabbageplantcannotformaheadandloses itseconomicsignificance. Iftheplant isyoungitdriesanddiescompletely.

Control measures


• Amongchemicalpreparationsusedagainstcabbagewhitebutterflyonvegetablecrops, effective results are brought by insecticides such ascypermethrin,deltamethrin,lambda-cyhalothrin,bifenthrin,malathion,imidaclopridandzeta-cypermethrin.

Cabbage Moth(Mamestrabrassicae)

Description:Thelengthofamaturelarvaofthecabbagemothisapproximately50mm.Itscolorvariesgreatly,startingwithgreenandendingwithblackcolors.Bodyhastwodottedlightlinesandadirtyyellowstripeonthesides.Ithasahorseshoe-shapedspoton topof thenext to the last segment.Withwings spread, this butterflyhas awingspanof50mm.Itsfrontwingsaredarkbrown,withayellowish-whitewave-likelineon theouteredge.Backwings, slightlydarkat the tips,are lighter incolor thanfrontwings.Eyesareroundishandcoveredwithshorthairs.Thispestoverwintersasapupa,inthesoil.ButterfliesbegintoleavethepupaeinaboutthemonthofMay.Somebutterfliesrequireadditionalnourishment,afterwhichtheybeginlayingeggsonthehostplants.Suchplantsincludebeet,soy,flax,sunflower,tobacco,peanut,etc.Thispestlayseggsinclusters,onthebottomsidesoftheleaves.Incaseofmassivereproduction,oneclustermaycontainupto100eggs.

A direct proportional relationship can be observed between pupal weight and butterflyfertility.Optimaltemperature forembryodevelopment is170 to20°C,whileair humidity is 70 percent. Larvae change their skin five times in the course theirdevelopment period, which lasts for approximately a month and a half. After finalchangeof the skin, larvaego into the soil to pupate.Theygodeeper inwinter andintocomparativelyupper soil layers in summer. In lowlandsofourcountry, thispestproducestwogenerationsayearandoneinthemountainzone.

Economic significance: The cabbage moth severely damages vegetable crops,especiallycabbage.Itslarvaegnawoncabbageleavesandmakelargeholes.Whenthecabbage forms a head, more mature larvae of the pest penetrate the head and gnaw itaswell.Rainwaterpenetratestheplantthroughholesproducedbylarvaeandbringwith them microorganisms which cause rot. As a result, the plant dies.

Control measures

• Fall plowing with cultivator;

Insects

Figure 13.23 Picture of cabbage stem weevil. Author:David’yan G.E.


• Destroyingplantremainsisimportant;

• Among chemical preparations used against cabbage moth on vegetable crops, effective results are brought by insecticides such asdeltamethrin, lambda-cyhalothrin,malathionandimidacloprid.

Cabbage Maggot(Hylernyabrassicae)

Description:Thefemaleimagoofthecabbagemaggotislightgreyandhasadarkbrownstripe,dividedintonarrowspots,onitsabdomen.Thelengthoftheflyis6to6.5mm.Malesareofthesamecolor,withthreedarkstripesonthedorsumoftheirthorax.Itsforeheadisfourtimesnarrowerthanitseyes.Thebaseofthehindthighsiscoveredwithfrequentlonghairs.

Larvaearecylindrical,whiteoryellowishincolor,withalengthof7to8mm.Theyoverwinterinthesoilinapuparium.Inspring,whentemperatureofuppersoillayersreaches12°C,flies leavethepuparium.Theseflies requireadditionalnourishment, forwhichtheytakenectarfromflowersofCruciferousplants.Afteradditionalnourishment,fliesbegintoreproduceandlayeggs.Theylayeggsingroups,onrootnecks,bottomof the stalk or directly in the soil, near the plants. During seedling planting, someeggsgowiththeseedlings.Oneflylaysupto100ormoreeggs.Durationofembryodevelopmentfluctuatesbetweenfourto10days.Thelarvalstagelastsforfromthreeto four weeks.

Negative economic significance: Pest activities mostly damage early varietiesof cabbage. Larvae damage cabbage roots, as a result of which the plant dies or its development is impeded.

Control measures

• Destroytheplantremainsleftafterthecabbagecropisharvested;

• Fall plowing with cultivation is recommended;

• Weedcontrolisimportant,especiallywithcruciferousplants;

• Timelyandhigh-qualityappropriatechemicaltreatmentisrecommended;

• Among chemical preparations used against cabbage maggot on vegetable crops,effectiveresultsarebroughtbytheinsecticidemalathion.

Cabbage Stem Weevil(Ceutorhynchusquadridens)

Description:Thelengthofthecabbagestemweeviladultis2.5to3.2mm.Itsbodyisblack,withthetopcoveredwithhairsandgreyscales.Thetrunkiscurvedandlocatedbetween the foundations of the front legs. Larvae are yellowish-white, with brownheads.Pupaeareayellowishcolor.Thepestoverwinters inplant remainsandunderfallenleavesorinthesoil.Inspring,thebeetlecompletesitsoverwinteringandbeginstofeedonthebottomsideofleavesofanycruciferaeplants. After cultivated cruciferous plantsappear, thebeetles thenmove to themand feeds, forwhich theymakesmallholesinleafstemsandstalks.Thispestlayseggsinthemainleafveinorthestalk.Eggsarelaidinsmallclusters(twotothreeunits)orsingleunits.Oneweevildepositsfrom20

Figure 13.22 Picture of cabbage maggot. Source: Delia Radicum Maine

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to40eggs.Atthistime,planttissue(underwhicheggsareplaced)bulges.Embryonicdevelopmentlastsfivetosixdays.Thispestproducesonegenerationperannum.

Economic significance: Larvae hatched from eggs make holes in the stems and stalks, feedon the stalk center andfill itwithexcrements. Finally, larvaegnawon the stalkdowntotherootneck,andthat ishowtheydescend intothesoil foroverwintering,wheretheymaketheircradleandpupate.

Control measures

• Destroyplantremainsaftercabbagecropisharvested;

• Fall plowing with cultivation is recommended;

• Weedcontrol,especiallyofcruciferousplants,isimportant;

• Among chemical preparations used against the pest on vegetable crops, effective resultsarebroughtbyinsecticidessuchasdeltamethrin.

OnionMaggot(Deliaantique)

Description:The mature larvae of the onion maggot are whitish in color, with a narrow frontpartandwiderear.Pupaearefoundinayellowishorreddish-brownfalsebag.Pupaehaveanegg-likeshapewithalengthofapproximately5to8mm.Imagobodylengthis6to8mm,withayellow-grayorlightgraycolor,blacklegs,andagreenishcolorontheback. Italsohasantennae(moustaches).Maleflieshaveverticaldarkbrownstripesontheirbackandabdomen.Onionmaggotsspendwintersinthesoil,atthedepthoffrom3to10meters,orinstorages.Theybegintoflyinearlyspring.Afteradditionalnourishment,fliesbegintolayeggsononionbrushes,inearthcrevices,andunderplantedonionscales.Eggsarelaidinclustersofupto10eggs.Oneflycanproduceupto100eggs.Temperaturegreatly affects thenumberof eggs that eachpest canproduce.Athigh temperatures(35°Candabove)theydonotlayeggs.Theprocessofegg-layingoccursmostlyinwarmanddryweather.Timeperiodofitsembryonicdevelopmentisdefinedatthreetoeightdays.Larvaldevelopmentcontinuesfor12to18,andlarvaethenpupateinthesoil.IntheterritoryofGeorgia,threegenerationsarecharacteristicofonionflies.Thefirstgenerationfliesout inthemiddleofApril, thesecondduringthefirsthalfofJune,whilethethirdcomes out in the second half of August.

Economic significance: The onion maggot host plants are seed onion, planted onion, garlic, leek,etc.Thisfly isoneof themajoronionpests,especiallydamagingtoseedonions. As a result, productivity diminishes significantly. Hatched larvae penetrateonionheadsandstartscarringthem,followedbypenetrationbymicroorganismswhichcauserot.Plantbulbsrot,whilebrushesofitsabove-groundorganswilt,yellow,anddie.

Control measures


• Use weed control;

• Plan to fall plow the harvested field;

• Seed material treatment;

• Incaseofnecessityofchemicaltreatmentagainstthepest,effectiveresultsarebroughtbyinsecticidessuchaschlorpyrifosandlambda-cyhalothrin.

Figure 13.24 Picture of onion maggot. Source: Plantvillage

Insects

Figure 13.26 Picture of carrot psyllid. Author: Joe Botting

Figure 13.25 Picture of carrot rust fly. Source: Agroatlas


CarrotRustFly(Psilarosae)

Description:Thecarrotrustflyisrelativelysmallinsize-about5mm.Itsabdomenandthoraxareshinyblack,theheadischestnut-coloredandthelegsareyellowish,whilethewingsaretransparent.Eggsaremilkywhiteandoval-shaped.Larvaearelegless,ashinylight-yellowcolorandtapertopointsatbothends,6to7mmlong.Pupaearelightbrown,4to5mmlongand0.9to1.3mmwide.Thispestoverwintersinthesoil,atthedepthof6to25cm.Soildepthdependsonthesoiltype,cultivationpeculiarities,andqualityofmoisture.PeststartstoflyoutinMaytoJune.

Economic significance: The carrot rust fly is a severepest of carrots, killingmanyseedlingsearlyintheyearormakingthefinalcropunsalableduetotheleveloflarvalmines,secondaryrotsandtheunevensizeofdevelopingroots.Damagedplantshavebluishleaves,whichturnyellowanddryuplater,andtherootsrot.

Control measures

• Croprotation-Observetheagro-technologyofcarrotproduction;

• Usetimelyandhigh-qualityappropriatechemicaltreatment;

• Incaseofnecessityofchemicaltreatmentagainstthepest,effectiveresultsarebroughtbyinsecticidessuchascypermethrinanddeltamethrin;

Timingofsprayscanbeaidedbymonitoringwithyellowtraps.Seethefollowinglink:http://smallfarms.oregonstate.edu/sfn/su08carrotrust

CarrotPsyllid (Triozaapicalis)

Description:Thematurepsyllidisyellowish-greenandabout2to2.5mmlong,withtwopairsofwingsandhindlegs.Nymphsareofgreenish-yellowishcolor,flat-shaped,withbulgingbacksofaslightlysilvercoloring.Matureinsectsoverwinteronconiferoustrees.Inspring,whencarrotsemerge,theymoveontotheleavesandbeginfeedingonthe plants.

Damagesymptoms:Curled leaves and stunted growth become visible on an average oftwodaysaftertheadultsenterthefield.Themigrationflightfromconiferstocarrotfields continues for several weeks.

Apart fromcarrot, thispest significantlydamagesparsleyandcelery.Partsof theplant, damaged by it, darken and dry. As a result of loss of juice, plant leaves curl,metabolismfails,leavesdryandfalldown.

Control measures

• Croprotation-InFinlanditwasfoundthatcovercropsweretheonlyeffectivemethodofprotectingtheyieldonorganicfarms;

• Observetheagro-technologyofcarrotproduction;

• Incaseofnecessityofchemicaltreatmentagainstthepest,effectiveresultsarebroughtbyinsecticidessuchascypermethrinanddeltamethrin.

Insects

Figure 13.28 Picture of beet leafminer. Source: Wikipedia

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Beet Weevil(Bothynoderespunctiventris)

Description:Maturebeetweevilsare1.2to1.6cmlong.Theirtrunkorproboscisisobtuse. Antennae are crooked. Their thoracic shield is wrinkled and covered with dots. Upperwingsarelinedwithverticalrowsofregularlyplaceddots.Thebodyofthebeetleisblack,butsinceitiscoveredwithcolorlessscales,itseemsgrayatfirstsight.Larvaeareupto20mminlength.Theyarelegless,whiteincolorandcurvedlikeanarc,withadarkbrownhead.Larvalbodiesconsistof12 segments.Ordinarily thebeetweeviloverwintersmostlyintheimagostage;however,afewalsooverwinterinthelarvalandpupalstage.Someofthebeetlesoverwinter(diapauses)inspring,whentemperatureof upper soil layers reaches 9° to 10°C,while others experience a lengthydiapausesandremaininthesoilforaboutayear.Afteroverwintering,beetlesrequireadditionalnourishmentforformingeggsandtheyfeedonbothbeetplantsandvariousweeds.InGeorgia,oneortwogenerationsperyeararecharacteristicofthispest.

Economic significance: This pest represents a significant threat to the beet crop. Adult beetles damage the leaves, while larvae damage the taproot. Beetle activities areespeciallydestructivewhentheplantsarenewlyemerged.Atthistime,thebeetlegnawsemergedplantsunderthecotyledon.Asaresult,theplantdies.

Control measures


• Control weeds;

• Deepploughingofthesoilisrecommended;

• In case of necessity of chemical treatment against the pest, effective resultsare brought by insecticides such aschlorpyrifos, chlorpyrifos-methyl anddeltamethrin.

Beet Leaf miner or Spinach Leaf miner(Pegomyiahyoscyami)

Description:Thelengthofamaturelarvais7to8mm.Itsbodyispaleyellowandlegless.Thefrontendof thebody ispointed,whiletwohookscanbeclearlyseenatthe around. The hind end is widened and terminates in triangular teeth. Small areas onbody segmentsare coveredwith tiny scalesbymeansofwhich the larvamoves.Lengthofamatureinsectis7to8mm.Malesaresmallerthanfemales.Abdomensofmales are smaller, while those of females are wide. Middle of the back and abdomen are dark ashen in color, sometimes reddish. There is a vertical stripe on the top side of the abdomen. The head is almost triangular, antennae have three digits.

Thepest’spupariummeasures4.5to5mminlengthandoval-shaped.Atthefirststageofdevelopment it is yellow, thendarkbrown, and thenblack. Beet leafminerwintersaspupariuminuppersoil layersandunderplantcover.Fliesbegintoflyoutin spring, when air temperature reaches 10° to 11°C. Process of laying eggs beginsseveraldaysafter theyflyout.Eggsare laid inclusters,onhostplant leaves.Embryodevelopmentrequiresaboutfivedaysinspringandlessinsummer.Thepestproducesabout 40 to 50 eggs in spring,while this number increases in summer generations.Newlyhatchedlarvaepenetratetheleafparenchymaandfeedonthepulp,asaresultofwhichmostoftheleavesarecoveredwithtunnels.Durationoflarvalphaseisdefined

Figure 13.27 Picture of beet weevil. Source: Zin Russia

Insects

Figure 13.29 Picture of beet caspid bug.Source: Agroatlas


atthreeweeks.Duringlarvalstage,thepestchangesitsskinfourtimes.Whengrowthiscompleted, larvaeeitherpupate in the tunnelorgo into thesoil, tooverwinter. InconditionsofGeorgia,threetofourgenerationsarecharacteristicofthispest.

Economic significance: As a result of pest larvae activity,most of the leaf area iscovered with tunnels. The tunneled area depends on the number of eggs, laid within each cluster. Damaged leaves fail to fully perform their functions, which negativelyaffectsbothquantityandqualityofthecropharvested.

Control measures

• Crop rotation;

• Cultivate and irrigate soil during the period when the pest is in pupal stage;

• Weed control;

• Incaseofnecessityofchemicaltreatmentagainstthepest,effectiveresultsarebroughtbymethomyl,andchlorpyrifos-methylisthesame.

Beet Caspid Bug(Poeciloscytuscognatus)

Description:Thewingsofthematurebugareyellow-darkbrownincolor,withablackpatternandav-shaped,triangularspot.Thethoraxisyellowishdarkbrown.Ithastwoblackspotsinthebackcornersofthefrontback.Wingsareglass-likeandtransparent.Lengthofthepest’sbodyis3to5mm.Larvaearegreen,withredeyesandablackroundspotonthetopsideofthemid-abdomenaswellastwoblackdotsontheshield.

Hostplantsofthispestinclude:beet,soy,sunflower,cannabis,flax,clover,bean,pea,lentil, etc.

Itoverwinters in theeggstage, in tissueof thehostplant stalkand leafveins. Inspring(endofMarch–beginningofApril),larvaehatchandsoonbegintofeedonthesameplantonwhichtheyhatched.Larvaepenetratetheplantwithitstrunkandsuckthe juice. Larval development continues for three to four weeks, after which it turns into amaturebug,thenitbeginstoreproduce.Sexuallymaturebugsbeginlayingeggsintheleafstemormainveinofthedevelopingbeetplant.Inordertolayeggs,bugspiercetheplant’ssurfacewiththeir trunkand layeggs intothetissue.Onlytheeggcanbeseenfromtheleaf,asasmalldarkdot.Thenumberofeggslaidbythepestdependsonthegeneration,environmentalconditionsandtypeofhostplant.Dependingonthesefactors,thenumberofeggsfluctuatesbetween20and2000.

Embryonicdevelopmentlastsfromfourdaystotwoweeks,dependingonclimaticconditions and the generation.

Economic significance: Apart fromdirectlydamagingbeetplants, the capsid canalsospread theviruscausingmosaicdisease.Emergedbeetplants,damagedby thepest,havestuntedgrowthanddiminishedproductivity.Inmostcases,damagedleavesoftheplantwiltbecomedeformed,anditdies.Plantsaredamagedevenmoreiftheyare infected with mosaic disease as result of pest activities.

Control measures

• Weed control in combination with fall plowing aids in managing the capsid;


Insects

Figure 13.31 Picture of potato tuber moth. Source: Microlepidoptera on Solanaceae

Figure 13.30 Picture of tortoisebeetle. Source: Wikipedia

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• Correct additions of mineral fertilizers;

• Incaseofnecessityofchemicaltreatmentagainstthepest,effectiveresultsarebroughtbytheinsecticidefenitrothion.

BeetTortoise(Tortoisebeetle)(Cassidanebulosa)

Description:Thebodyofthebeettortoise isflat. Itspronotumandelytraarewideandcovertheheadfromthetop.Upperwingsarealsosowidethattheycoverthebody.Thebeetleisrusty-brownontop,withirregularblackdots.Deeplinesareclearlyvisibleonupperwings, inwhich thereareverticallyplaced largedots.Body isblackon thebottom,withalengthof6-7mm.

Edgesofamaturelarva’sbodyarejagged,soendsofsegmentsareclearlyvisibleasprotrusions.Ithastwotailprotrusions,lengthofwhichisonethirdofthebody.Pestoverwintersintheadultphase.Inspring,overwinteredbeetles,afteradditionalfeedingonsaltbush andpigweed,begintolayeggsontheleavesofthesesameplants.Eggsare laid on both sides of the leaves, in clusters. The beet tortoise covers its eggs on top with secretion.

Economic significance: Pest larvae gnaw on the leaves and pupate right there. The tortoise beetle has double economic significance.Ononehand, this is a pest thatsignificantlydamagesthebeet;ontheotherhand, it isausefulspeciescontrollingthedevelopmentofweedsofthegoosefootfamily.Thebeetisdamagedbyboththebeetles and the grubs. The grubs of fourth and fifth in stars are the most voracious, consuming about 87 percent of the total food volume needed for their wholedevelopmental period. The beetles are the most voracious after emergence from pupaeandafterhibernationbeforeovipositor.Theyeatawaytheroundholesinaleafplate, not damaging veins; whereas the grubs scrape off the leaf pulp on the lower sidebetweenveins,leavingtheupperrinduntouched.Theseverelydamagedleaveshavealacyappearance.

Control measures


• Incaseofnecessityofchemicaltreatmentagainstthepest,effectiveresultsarebroughtbyuseoftheinsecticidechlorpyrifos-methyl.

Potato Tuber Moth(Phthorimaeaoperculella)

Description:The head of the larva is dark brown, with black shields and three hairs at the foundationsof false legs. It has sixdark shieldson thebottomof the secondsegmentof theabdomen.Lengthofamature larva isabout10to12mm,withpinkoryellowishwhitecoloring.Themothhasawingspanof12to16mm.Theabdomenispalegreyfromthebottomandyellowish-greyfromthedorsalside.Frontwingsaresilver-ashen,withdarkspotsonthebackedge.Eggsaremotherofpearly-whiteandovalinshape,withthediameterofabout0.8mm.

Pestreproducesbothinthefieldandinstorage.Itresistslowtemperatureswelland,apart fromcultivatedplants, can feedonweeds representing theSolanaceae family.

Insects


Thesecharacteristicssignificantlycontributetoitsacclimatizationandreproductioninnew areas.

Economic significance: As it has been noted above, this pest damages potatoes bothinthefieldandinstorage.Inthefield,itlayseggsonthebottomoftheleavesofpotatoesandotherplantsrepresentingtheSolanaceaefamily.Hatchedlarvaebegintofeedontheleaves,asaresultofwhichtunnelsappearonthem.Also, larvaeseverelydamage the plant’s stems and stalks.

Duringpotatostorage,themothlayseggsonpotatotuberbuds.Larvae,hatchedfrom the eggs, penetrate tubers and damage their pulp. Tuber skin, at the points of penetrationby larvae, becomespink or violet. Also, larva excrements accumulate inthese areas.

Control measures

• Weed control;

• Observeoptimaldeadlinesforcropharvesting;

• In case of necessity of chemical treatment against the pest, effective resultsarebroughtbyuseof insecticides such as cypermethrin, imidacloprid, alpha-cypermethrin, dimethoate, deltamethrin, lambda-cyhalothrin, methomyl, andcarbosulfanandzetacypermethrin.

Insects

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Chapter 13

INTEGRATEDPESTMANAGEMENTOFVEGETABLECROPSINGEORGIA

One of the first people to understand the relationship of insects to their naturalenvironmentwasanentomologistbythenameofStephenAlfredForbes.In1880,Forbesdocumentedthefeasibilityofecologicalmanagementapproachestoinsectcontrol.Headvocatedanecologicalapproachandcombinationsof resurgenceofprimarypests,selection of strains of pests resistant to insecticides and the general contamination of the environment. Although the term pest management seems new in controlling pests it is based on decades of development. Forbes is said to be the first to work on various features in shaping of what we now term integrated pest management.

Extensiveprogresswasmadeduringthenexthalfcenturyinlayingthefoundationforappliedecologythroughinvestigationsofculturalpractices,includingcroprotations,tillage, the identification of resistant varieties of crops, to the conservation of natural enemies,andtheimportationofexoticbiologicalcontrolagents.

About the time of the Second World War, a time of multiple advances dominated bythediscoveryanddevelopmentofsuccessivegenerationsofchemicalinsecticides;the arsenicals and the fluorides, the organochlorines, the organophosphates, thecarbamates,andthepyrethroids.Eachsuccessivegroupseemedtobemoreeffectivethanitspredecessorsandmorelikelytoreducetheintensityandeventheexpectationthat some insect pests might even be eradicated. In the excitement and euphoriasurroundingtheuseofthesepowerfultools,thenatural lawsofecologywereallbutforgotten,untilwewereallawakenedbyRachelCarson’sbook,“SilentSpring”in1962.Thatbooksinglehandedlychangedinsectmanagementforever.

Thenewideaof“IntegratedPestManagement”startedtogainmomentumintheearly1960’swiththepublicationofSilentSpring,whichservedasawarningintheoveruseofthenewmiracleinsecticides:DDT,otherchlorinatedhydrocarbonpesticides,broadspectruminsecticidesingeneralwereposingadangertomanandtheecologyoftheplanet due to their wide usage throughout the world. This was a turning point causing agriculturists,extensionspecialist,chemicalcompaniesandresearcherstorethinkthemostlogicalwaystomoveforwardandutilizemethodswhichare‘sustainable’andnottobecompletelydependentonchemicalcontrol.

In1959alandmarkpaperwaspublishedbyStern,Smith,vandenBosch,andHaganthat outlined the integrated control concept of combining natural and applied control measuresandprovidedaphilosophyforinsectcontrolthatleddirectlytothecurrentinterpretationofIPM.

Therearemanydefinitionsofintegratedpestmanagementofinsects.Thefollowingdefinitioncoversallofthemajorfacetsandisgenerallyacceptedbymostgovernmentand local agencies worldwide. “Integrated pest management (IPM) is an ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and use of resistant varieties. Pesticides are used only after monitoring indicates they are needed according to established guidelines, and treatments are made with the goal of removing only the target organism. Pest control materials are selected and applied in a manner that minimizes risks to human health, beneficial and non-target organisms, and the environment”. (Developed by the University of California - IPM)

Someof thefirstdescriptionsof integratedpestmanagementhadvery longandoutlandish termswhichmade it sound extremely complicated.However, in 1972, R.L. Rabb simplified thedefinition as“the intelligent selection anduseofpest controlactionsthatwillensurefavorableeconomic,ecological,andsociologicalconsequences”.


Insects

InsectManagementStrategiesEffective insect and mite management involves multiple facets, all with one common

goalinmind:sustainability.Vegetablecropsareattackedbyanoverabundanceofinsectsandrelatedpestswhichthebuyerswouldratheravoid.Perhapsevenmoreimportantisthedamagecausedbytheinsectswhichlowersvegetablequality.HereareafewofthefacetswhichareconsideredforGeorgianvegetableproduction.Theseconsiderationsare general and apply formost pestmanagement programs.They are not exclusiveandwith timewillmost likelybemodifiedas theyare improvedonby researchandexperience,alwaysseekingtofindbetterwaystomanage insectandmiteproblems.IPMseekstheoptimalcombinationoftacticstoreducevegetablepestpopulationsinordertomakeiteconomicallyfeasibledevoidofadverseeffectsonthefarmortotheenvironmentandalwayswiththebuyingpublicinmind.

KnowyourpestsFirstofallitisimportanttoknowtheidentityofthekeypestinsectsandmitesand

beneficialorganismsyouaredealingwith.Thiscanbeconfirmedbyyourlocalextensionpersonorbytakingafewclose-uppicturesandsendthemtopersonsworkingwiththecropinyourarea.Misidentificationscanbeverycostly.Keepinmindthatnotallinsectsandmitesareharmful.Infact,quiteafewarebeneficial.

Properly identifying pests is the foundation onwhich a good insectmanagementprogramisbuilt.Ifthepestisnotproperlyidentified,thechancesofselectingthecorrectcontrolstrategiesaregreatlydiminished.Manyinsectsandmitescanbecorrectlyidentifiedsimplybecausetheyareencounteredsooften.However,itneverhurtstobackupyourknowledge base with some reference materials. Beneficial organisms can be important components of an effective insect management program. Being able to distinguish the goodguysfromthebadguysmayhelpyouavoidunnecessaryandpossiblydisruptivepesticide sprays. Some commonpredators that all growers shouldbe able to identifyincludeladybeetlelarvaeandadults,lacewinglarvaeandadults,andsyrphidflylarvae.Accesstotheinternetisveryvaluableinfindingpictureofbothbeneficialandpestspecies.

Crop rotationIs a systematic approach to deciding which crops to plant where in vegetable

productionfromyeartoyear.Croprotationiswhereacertaincropcanbegrownonlyayearorashortperiodofyearsandthendiscontinuedforagivennumberofyearsbeforeit is planted again. Here we are concerned with insects and mites as well as nematodes anddiseaseswhich cannot generally survivewithout a certain groupof host plantswhichtheydependonforsurvivalandmultiplication.Byrotatingthecropplanteditis possible to eliminate the host plant and its relatives and thus get rid of a portion of the pests in that area. Thus, here is another practice without the use of chemicals which worksverywelltodrasticallymitigatesomeinsectsandrelatedpests.

The goal of crop rotation is to help avoid or reduce problems with soil borne organismssuchasnematodesofpotatoandsomesoil-dwellinginsects inadditionitalsohelpsmanagesoil fertility.Weknow forexample that rotationworks inGeorgiafor:potatorotnematode,onionthrips,andcarrotrustfly.Rotatingcanalsoreducetheseverityofanumberofotherpestproblems.Forexample,byrotatingpotatofieldsyoucangreatlyincreasetheamountoftimeittakesColoradopotatobeetlestocolonizeafield,therebyreducingthetimethebeetleshavetoincreasetodamaginglevels.Don’tplantcropsthataresusceptibletowirewormdamageinfieldsthatwerepreviouslyinsodorheavily infestedwithgrassyweeds. Inaddition, it is agood ideanot toplant

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cabbageoronionsnexttosmallgrainfields,becauseonionthripsbuilduptoveryhighlevelsinsmallgrainsandwhentheyareharvestedordrydowntheynormallymoveintocabbage or onions.

TillageBytillingorcultivatingthesoilinsectsaregreatlyaffecteddirectly,bythetextureof

the soil and its chemical composition, the percentage of soil moisture, the temperature, andothersoilorganismsand,indirectlybytheirinfluenceonthehostplant.Tillinghasatendencytobringpupae,maturelarvaeandadultinsectstothesurfacewheretheyaredealtwithbytheelementsandnature,suchasbirds,predaciousinsectsandothernaturalenemies.Smallrodentseatalotoftheinsectsthatareexposedonthesurface.Tillageinthefallandcropdestructionreducesinsectpopulationsbycrushingthemorbydestroyingtheirover-winteringhabitat,exposingthemtoharshweatherconditions.Inthispublicationwerecommendcultivationtoaid inthecontrolof insectpestsforseveral crops. Tillage can be used to reduce Colorado potato beetles and to diminish wire worm populations.

Preventativepestmanagementtechniques Selecting and using preventative pest management techniques can be effective

andisusuallylessexpensivethaninsecticideapplications.Thereareanumberofpracticesthat can reduce insect numbers before you actually see the insects in the field. Often,decisionsaboutthesepracticesmustbemadebasedonpastexperiencewiththeinsectratherthancurrentknowledgeoftheseverityoftheinfestation.Manyofthesepracticesare goodmanagement practices forweeds and diseases aswell, so they can easily beincorporatedintoanoverall insectmanagementprogram.youwillnoticethenumberoftimesthatitisrecommendedinthemanagementofGeorgianvegetablepests.Itisadvisabletoutilizethedestructionofcropresidueandweedremovalinordertodelayanddeterthebuild-upofnoxiousinsectandmitepests.Thisisanexcellentwaytodelayanddiscouragesuchpests.ItisrecognizedthatInsectstendtobecomeactiveatspecifictimeseachyear,varyingthetimeofplantingcansometimeshelppreventseriousinsectproblems.

Host plant resistance:Isaveryimportantmechanismandisusedagreatdealtodayincertaintypesofplantswherewehaveresistancetopestdamageofmajorimportance.Developingresistantcultivarsbytraditionalbreedingmethodsisgenerallyslowandaratherinexactprocess. Butnewadvancesinbiotechnologynowmakeitpossibletotakespecificgenesfromoneorganismandinsertthemintothecellsofacompletelydifferentspeciesleadingtoaplantthatisresistant.InGeorgiaseveralinsectresistantcultivarsofvegetableplantsareavailable.This isan ideal strategy toavoidpesticideapplications.Planningforthisaspectofmanagementmuststartearlywiththechoiceof cultivars to be utilized.

Attractants and repellents: Are useful tools in certain situations to prevent an insect frombuildinguptoeconomicinjurylevels.Insuchcasesovertheperiodofonlyayearorsothepestpopulationcanbereducedtoinsignificantnumbersjustbytrappingout.Inordertogetridoftheadultsthatarecapturedtheyneedtoberemovedfromthetrapsanddiscarded.Thisisaverysmellyactivitybecausetheyusuallydieinthetraps.Thus,itisrecommendedtoburysuchcollections.

Likewiserepellantsattimescanbestrongdeterrentsandactuallykeepavegetablecropsafefromspecificinsectpests.Thisismorecommonlyachievedinhomegardensbyplantingherbswhichrepelinsectsornematodes.Acoupleofexamplesare:basilwhich


Insects

repelsthecarrotflyadults;catnipwhichrepelsthecabbagelooperandtheColoradopotatobeetle;andchivewhichrepelscarrotflyandaphids.Manyothercombinationshave been reported.

Trap Crops: There are a few instances where trap crops have given protection to a crop.Atrapcrop isaplant thatattractsagriculturalpests,usually insects,away fromnearbycrops.Atrapcropscanbeplantedaroundthecircumferenceofthefieldtobeprotected,orinterspersedamongthem.Thebenefitsoftrapcroppingare:betterqualityof themainproduce; attract beneficial organisms; enhancebiodiversity; and reducedependence on insecticides.

Anotherwaytouseatrapcropistousethesameplantcultivarasthemaincrop.The trap crop is planted much earlier than the main crop in order for it to serve as food fortheinsects.Asecondmethodistousetwoentirelydifferentspecies.Researchhasshownthatearlyplantedtomatoescanserveastrapcropsformultiplepeststoprotectaplantingofdesirabletomatoes.Thismightbetestedinyourfieldsonasmallscaletoseewhatkindofresultsyoucanobtain.

Monitoring the current status of insects and mites: Vegetable growers must make insect and mite pest management decisions on an almost daily basis during thegrowing season. To make the best decisions, it is often useful to have information regarding the current status of a pest’s population. This can be accomplished through some sort of sampling or monitoring program. There are several methods to monitor insect populations.

Themostcommonmethodformonitoringinsectsisbyscoutingfields.Scoutingcanbe formal, such as counting insects on a given number of plants throughout the field, or it can be informal, with the grower walking through the field and looking for insects ontheplants.Formalscoutingmaybemoreaccurate,but themost important thingisforgrowerstoregularlywalktheirfieldslookingforinsectsorinsectdamage.Somepests,suchasmites,mayrequiretheuseofahandlensinordertoseethem.Othersmayrequiretheuseofequipmentsuchasasweepnetorabeatingcloth.Mostcanbemonitoredjustbycloseinspectionoftheplants.Weeklymonitoringcountsofgivensizewith a set number of counts per hectare will allow growers to compare results from one week to another to make informed management decisions.

Chemical attractants: Areusedinconjunctionwithsimplestickytrapstomonitorinsect populations in relation to the economic thresholds and also to lure insects to toxicbates.Pheromonetrapsareoftenusedtodeterminewhenmothsareflying.Thisinformationcanbeusedinseveralways.First,catchingmothsinastickytrapcanalertgrowers to begin looking for the pest in the field. This can save time because the grower won’t be looking for the pest before it is present. Second, pheromone trap catches can beusedtotimeinsecticideapplications.Third,forsomepests,theneedtospraycanbedetermined from the number of moths caught in the trap. Pheromones are available for afewofthemoth/caterpillarpestsofvegetables.

ControlbyChemicalsSelecting the proper pest control option is often dependent on the grower’s

knowledgeofthepestcomplexthepreviousyearandtheinsectsthathavebeenbadinpreviousseasons.Indealingwithvegetablecrops,theselectionofacontroloptionsduringthegrowingseasonusuallymeansnotsprayingorselectingapesticide.Althoughwealwaysencouragegrowerstoreadandfollowlabeldirections,theoneareawherethelabelisnotalwaysthebestsourceofinformationisconcerningwhichinsectstheinsecticide will control.

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The insecticides recommended in this book, for control of various pests, are listed becausetheyhavebeenfoundtobeeffectivebygrowershereinGeorgia.Considerationsthatshouldbeexaminedare:insecticidecosts,applicationcosts,relativeeffectiveness,andgain inprofitsthatcanbeexpectedfromtheapplication,whether itwillcontrolotherpests,andhowitwillaffectpredators,parasites,andpollinators.Itshouldalwaysbe remembered that pest control materials should be selected and applied in a manner thatminimizes risks to humanhealth, beneficial and non-target organisms, and theenvironment.

Evaluating the effectiveness of previously used control options: Growers shouldalwaysevaluatetheeffectivenessofapestcontrolaction.Inspectingthefieldacoupleof days after an insecticide is appliedwill help the grower determine the necessityfor additional control measures in that field, as well as provide information about the insecticide’seffectivenessforfuturereference.Growersshouldpayattentiontowhethertheinsecticidekilledallstagesofthepestsorifonlysmalllarvaeornymphswerekilled.Theyshouldalsonoticetheeffectsonotherpestsinthefieldandonbeneficialinsects.

Natural control: Isawayofconservingnaturalenemiesallowingthemtoeffectivelyreducepestpopulationsanddamage.Thiscanbeaccomplishedinseveralways,butthemostimportantisreducingthenumberofinsecticideapplications.Eachtimeasprayisapplied, more predators and parasites are killed. When deciding to use an insecticide, youshouldconsidertheimpactthatapplicationwillhaveonbeneficialinsects.Bacillusthuringiensisproducts,forexample,arenotknowntoharmbeneficialinsects.

Pollination of Vegetable Crops in Georgia: Pollination by bees is critical for thesuccessfulproductionofmelon,watermelonandcucumbers.Thecommonhoneybeeisoftenusedeffectivelytopollinatethesecrops.However,itisimportanttoremembertheimportanceofournativebees.Theyareactuallymoreeffectivethanhoneybeesinmost cases. Melons and cucumbers can be hand pollinated; however, this is tedious and time consuming.

Always try to protect your pollinators from exposure to insecticides and wherepossiblechoosepesticidesthatareleasttoxictobees.Applypesticideswhenbeesarenotactivelyforaging.Honeybeesandmanynativebeesareactiveprimarilyduringthemorning and early afternoon.Many pesticides can be effectively applied in the lateafternoonoreveningwithrelativesafetytobees.Eveningtreatmentsarealsoknowntoaidinthecontrolofmothpeststhatareactivelylayingeggsatnight.

Biological Control: Dealswiththeintroduction,encouragementandmultiplicationof natural enemies for the suppression or control insect pests. This form of control is alsoconsideredpartofgrowingcropsorganicallywith littleorno insecticidesbeingallowed.Itispossible,butdifficult,toincorporatetheintroductionandmultiplicationofparasites, predators and diseases where chemical pesticides are being utilized. However, itisalwaysencouragetryingtoprotectthemiftheyarenaturallyintheIPMarea.Thiscan be accomplished as with pollinators; choice of pesticide, timing of applications and applicationtargetingtechniques.

Manyof the key facetsof IPMhavebeen coveredhere, yet there areothers thathave not in this brief summary. However, you are now aware of themany complexissuesthatareincorporatedintothemammothscopeofIntegratedPestManagement.Tobe sure, it is not a static theory. It is alive andever changing.Asnewandbettermethodsarediscoveredthatareeconomicallyfeasibletheywillbeincludedunderthishugeumbrella.However,rememberthattheprimarygoalofIPMisthatitleadsustosustainability.


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191

AAcervulus - A subepidermal, saucer-shaped, asexualfruitingbodyproducingconidiaonshortconidiophores.

Aecium - A cup-shaped fruitingbodyof the rust fungiwhich produces aeciospores.

Anomorph-Theimperfectorasexualstageofafungus.

Anthracnose - Adisease that appears as black, sunkenleaf, stem, or fruit lesions and caused by fungi thatproducetheirasexualsporesinanacervuli.

Apothecium -Anopencup-orsaucer-shapedascocarpofsomeAscomycetes.

Ascocarp-ThefruitingbodyofAscomycetescontainingasci.

Ascomycetes- A group of fungi producing their sexualspores, ascospores, within asci.

Ascospore-Asexuallyproducedsporeborneinanascus.

Ascus-Asaclikecellofahyphainwhichmeiosisoccursandwhichcontainstheascospores(usuallyeight).

Asexual reproduction - Any type of reproduction notinvolving the union of gametes or meiosis.

BBacillus-Arod-shapedbacterium.

Bacteriophage-Avirusthatinfectsbacteriaandusuallykills them.

Basiciomycetes-Agroupoffungiproducingtheirsexualspores, basiciospores, on basidia.

Basidiospores - A sexuallyproduced spore, borneon abasidium.

Basidium-Astructureonwhichbasidiosporesareborne.

Glossary

CCanker - A necrotic, often sunken lesion on a stem,branch, or twig of a plant.

Chlamydospore-Athick-walledasexualsporeformedbythemodificationofacellofafungushypha.

Chlorosis - yellowing of normally green tissue dueto chlorophyll destruction or failure of chlorophyllformation.

Cleistothecium-Anentirelyclosedascocarp.

Conidiophore - A specialized hypha on which one ormore conidia are produced.

Conidium - An asexual fungus spore formed from theend of a conidiophore.

Culture-Artificiallygrownmicroorganismsonapreparedfood material.

Cyst -Anencystedzoospore (fungi); innematodes, thecarcass of dead adult females of the genera Heterodera orGloboderawhichusuallycontaineggs.

DDikaryotic-Myceliumorsporescontainingtwosexuallycompatiblenucleipercell-commoninbasidiomycetes.

Disease cycle -The chainof events involved indiseasedevelopment, including the stages of development of the pathogen and the effect of the disease on the host.

EEctoparasite - A parasite feeding on a host from theexterior.

Enation -Tissuemalformationorovergrowthinducedbycertain virus infections.


Endoparasite-Aparasitewhichentersahostandfeedsfrom within the host.

Flagellum - A whip-like structure projecting from abacterium or zoospore and functioning as an organ of locomotion.

GGum - Complex polysaccharidal substances formed bycells in reaction to wounding or infection.

HHaustorium - A simple or branched projection ofhyphae into host cells which acts as an absorbingorgan.

Host - A plant that is invaded by a parasite and fromwhich the parasite obtains its nutrients.

Host range - The various kinds of host plants that areattackedbyaparasite.

Hyaline-Colorlesstransparent.

Hyperplasia -Aplantovergrowthdue to increasedcelldivision.

Hypertrophy-Aplantovergrowthduetoabnormalcellenlargement.

Hypha-Asinglebranchofamycelium.

IImperfectfungus-Afungusthatisnotknowntoproducesexualspores.

Imperfect stage -Thepartof the life cycleof a fungusinwhichnosexualsporesareproduced.Theanamorphstage.

Indicator - A plant that reacts to certain viruses orenvironmental factors with production of specific symptomsandisusedfordetectionandidentificationofthese factors.

JJuvenile - The life stage of a nematode between theembryoandtheadult;animmaturenematode.

LLocal lesion -Alocalizedspotproducedonaleafuponmechanical inoculation with a virus.

MMummy-Adried,shriveledfruit.

Mycelium-Thehyphaormassofhyphaethatmakeupthebodyofafungus.

NNoninfectious disease - A disease that is causedby anabioticagent,thatis,byanenvironmentalfactor,notbya pathogen.

OObligateparasite-Aparasitethatinnaturecangrowandmultiplyonlyonorinlivingorganism.

Oomycete - A fungal-like chromistan that producesoospores.

Oospore-Asexualsporeproducedbytheunionoftwomorphologically different gametangia (oogonium andantheridium).

PParasite - An organism living on or in another livingorganism(host)andobtainingitsfoodfromthelatter.

Pathogen -Anentity,usuallyamicroorganismthatcanincite disease.

Pathovar-Inbacteria,asubspeciesorgroupofstainsthatcaninfectonlyplantswithinacertaingenusorspecies.

Perfect stage-Thesexualstageinthelifecycleofafungus.

Phytoplasma -Mollicutes that infectplantsandcannotyetbegrowninculture.

Primary infection -The first infectionof a plant by theoverwintering or oversummering pathogen.

Prokaryate - A microorganism whose genetic materialis not organized into a membrane-bound nucleus, forexamplebacteriaandmollicutes.

193

Pustule-Smallblisterlikeelevationofepidermiscreatedas spore form underneath and push outward.

Pycnium - Also called spermagonium. In somebasidiomycetes,itcontainsthespermatiaandreceptivehyphae.

Pycnidium - An asexual, spherical, or flask-shapedfruitingbodylinedinsidewithconidiophoresproducingconidia.

Pycniospore-Alsocalledspermatium.Asporeproducedinapycnium.

RRingspot-Acircularareaofchlorosiswithagreencenter;asymptomofmanyvirusdiseases.

SSaprophyte - An organism that uses dead organicmaterial for food.

Sclerotium - A compact mass of hyphae with orwithouthosttissue,usuallywithadarkenedrind,andcapable of surviving under unfavorable environmental conditions.

Sexual-Participatinginorproducedasaresultofaunionof nuclei in which meiosis takes place.

Spiroplasmas - Pleomorphic, wall-less microorganismsthatarepresentinthephloemofdiseasedplants.Theyare often helical.

Sporangium -A containeror caseof asexual spores. Insome cases it functions as a single spore.

Spore - The reproductive unit of fungi consisting ofone or more cells; it is analogous to the seed of green plants.

Sporadochium - A fruiting structure consisting of acluster of conidiophores woven together on a mass of hyphae.

Stylet - A long, slender, hollow feeding structure ofnematodes and some insects.

Systemic - Spreading internally throughout the plantbody.

TTelemorph-Thesexualorso-calledperfectgrowthstageor phase in fungi.

Teliospore-Thesexual,thick-walledrestingsporeoftherust and smut fungi.

Telium -Thefruitingstructure inwhichrust teliosporesare produced.

VViroid - Small, low-molecular-weight ribonucleic acid(RNA) that can infect plant cells, replicate themselves,and cause disease.

Virus-Asubmicroscopic,obligateparasiteconsistingofnucleic acid and protein.

ZZoospore - A spore bearing flagella and capable ofmoving in water.

194 ბოსტნეული და ბაღჩეული კულტურების ძირითადი მავნებელ-დაავადებები და მათ წინააღმდეგ ბრძოლა საქართველოში

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2.2 Symptomsofphomophsisblight(n.d.) InWikigardener,Retrievedhttp://gardener.wikia.com/wiki/Phomopsis_blight?file=Aubergine_Phomopsis_Vexans.jpg

2.3 Symptomsofverticilliumwilt(n.d.)AuthorLindseyduToit,Retrievedhttp://mtvernon.wsu.edu/path_team/Dis-easeGallery/eggplant-verticillium-wilt-2.htm

2.4 Symptomsofalrenariasolaniineggplant(n.d.)InPlantVillage,Retrievedhttps://www.plantvillage.com/en/top-ics/eggplant/infos/diseases_and_pests_description_uses_propagation

2.5 Symptomsofcucumbermosaicvirus(n.d.)InDiseases-PepperandEggplant,Retrievedhttp://www.semena.org/agro/diseases4/tobamovirus-e.htm

2.6 Symptomsofstolburineggplant(n.d.)InLegumicultura,Retrievedhttp://www.legumicultura.ro/content/vinete.php

2.7 Symptomsofbacterial spot ineggplant (n.d.) InCanadianFood InspectionAgency,Retrievedhttp://www.in-spection.gc.ca/DAM/DAMimages/pestrava_ralsol_factsheet1328250272131eng.jpg

2.8 Symptomsofchillinginjury.(n.d)InCanadianFoodInspectionAgency,Retrievedhttp://www.inspection.gc.ca/DAM/DAM-plants-vegetaux/ralsol_factsheet_image7_1328250272131_eng.jpg

3.1 Symptomsoflateblightinpotato(n.d.)AuthorJeanRistaino,Retrievedhttp://usablight.org/

3.2 Symptomsoffusariumdryrotonpotato(n.d.)InUneceOrganization,Retrievedwww.unece.fusariumrot.jpg.org

3.3 Symptoms of potato canker (n.d.) In Inspection Canada, Retrieved http://www.inspection.gc.ca/DAM/DAM-plants-vegetaux/STAGING/images-images/pestrava_synend_factsheet_image2_1327933156339_eng.jpg

3.4 Symptomsofpotatopowderyscab(n.d.)InWikipedia,Retrievedhttps://en.wikipedia.org/wiki/scabpotato


3.5 Symptomsofearlyblightinpotatoleaf(n.d.)AuthorTomLeroy,Retrievedhttp://www.gardeningwithtomleroy.com/wp-content/uploads/2013/04/Early-Blight-of-Potato1.jpg

3.6 Symptomsofcercosporaleafblotch(n.d.)AuthorBobSouvestre,Retrievedhttps://laplantpath.wordpress.com/page/8/

3.7 Symptomsofrhisoctoniaofpotatotuber(n.d.)InMichiganUniversity,Retrievedhttp://www.potatodiseases.org/rhizoctonia.html

3.8 SymptomsofpotatovirusXonleaves(n.d.)InCIPpotato,Retrievedhttp://cropgenebank.sgrp.cgiar.org/index.php/management-mainmenu-433/stogs-mainmenu-238/clonal-crops/protocol-validation/potato/viruses

3.9 Symptomsofaucubamosaicvirusonleaves(n.d.)InWikipediaenFrance,Retrievedhttp://fr.academic.ru/dic.nsf/frw/2032912

3.10 Symptoms of potato virus S on leaves (n.d.) In AHDB, Retrieved http://potatoes.ahdb.org.uk/media-gal-lery/13214/2651

3.11 Symptomsofpotatovirusyonleaves(n.d.)Inwikigardener,Retrievedhttp://gardener.wikia.com/wiki/File:Pota-to_Virus_y_Leaf_2.jpg

3.12 SymptomsofpotatovirusMon leaves(n.d.) In Ibricorg,Retrievedhttp://www.ibric.org/species/pvirus/detail.php?No=72

3.13 Symptomsofblacklegonpotatotuber(n.d.)InUniversityofMoscow,Retrievedhttps://www.google.ge/webh-p?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=university+of+Moscow+plant+pathology

3.14 Symptomsofbacterialsoftrot(n.d.)AuthorEdwards,Don.Retrievedhttp://postharvest.ucdavis.edu/pfvegeta-ble/PotatoesEarlyPhotos/?repository=29974

3.15 Symptomsofpotatoheatnecrosis (n.d.) InPotato InspectionCanada,Retrievedhttp://www.inspection.gc.ca/plants/potatoes/guidance-documents/pi-009/eng/1383933490053/1383934020925?chap=9

3.16 Symptomsofhollowheartinpotato(n.d.)InGardeningKnowHow,Retrievedhttp://www.gardeningknowhow.com/edible/vegetables/potato/potato-hollow-heart.htm

3.17 Symptomsofpotatoblackheart(n.d.)InNorthernDakotaStateUniversity,Retrievedhttps://www.ag.ndsu.edu/cpr/images/5-22-14/plsci-blackheart.png

3.18 Symptomsofmisshapenpotato tubers (n.d.) In friedtofublog, Retrievedhttps://friedtofublog.files.wordpress.com/2012/10/fingerling_potatoes.jpg

3.19 Symptomsofphysiologicalleafrollofpotato(n.d.)InPotatoInspectionCanada,Retrievedhttp://www.inspec-tion.gc.ca/plants/potatoes/guidance-documents/pi-009/eng/1383933490053/1383934020925?chap=9

4.1 Symptoms of powdery mildew in cucumber (n.d.) In Vegalab, Retrieved http://vegalab.tw/wp-content/up-loads/2015/06/Powdery-Mildew-on-Cucumber-Leaf.jpg

4.2 Symptomsofsclerotiniarot(n.d.)InSclerotiniaOrganisation,Retrievedhttp://www.sclerotia.org/lifecycle/infec-tion

4.3 Symptoms of black root rot (n.d.) Author Jason Brock. Retrieved http://www.ipmimages.org/browse/detail.cfm?imgnum=5436381

4.4 Symptomsofanthracnoseoncucumber(n.d.)InGrowLust-GrowinganEdibleGarden,Retrievedhttp://growlust.com/anthracnose_on_zucchinis/

4.5 Symptomsofgummystemblight(n.d.)AuthorDonFerrininie,Retrievedhttp://www.gardeningknowhow.com/plant-problems/disease/gummy-stem-blight-control.htm

4.6 Symptomsofcladosporium(n.d.) InForestry Images,Retrievedhttp://www.forestryimages.org/browse/detail.cfm?imgnum=1534032

4.7 Symptomsofdowneymildewoncucumber(n.d.)InStateUniversityCooperativeExtension:PestNews,Retrievedhttp://www.ces.ncsu.edu/wp-content/uploads/2013/06/cucumber_cucurbit_downy_midlew_top.jpg

4.8 Symptomsofalternarialeafspot(n.d.) InGardeningKnow-How:AuthorHowardFSchwarts.Retrievedhttp://www.gardeningknowhow.com/plant-problems/disease/alternaria-leaf-spot.htm

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4.9 Symptomsofcucumbertargetspot(n.d.).InForestryImages,Retrievedhttp://www.Forestryimage/plant-prob-lems/disease/alternaria-leaf-spot.htm

4.10 Symptomsoffusariumstemandrootrot(n.d)InAppliedandEnvironmentalMicrobiology.Retrievedhttp://aem.asm.org/content/68/8/4044/F4.large.jpg

4.11 Symptomsof cucumbergraymold (n.d.). InAmericanPhytophatologySociety,Retrievedhttp://www.apsnet.org/publications/imageresources/Pages/IW000077.aspx

4.12 Symptomsofcucumbermosaicvirus(n.d.).AuthorWilliamMBrown,Retrievedhttp://www.gardeningknowhow.com/edible/vegetables/cucumber/cucumber-mosaic-virus.htm

4.13 Symptomsofcucumbergreenmottlemosaicvirus (n.d.). InSnipview,Retrievedhttp://www.snipview.com/q/Cucumber_green_mottle_mosaic_virus

4.14 Symptomsofpseudomonasburgeri(n.d.).InSnipview,Retrievedhttp://www.snipview.com/q/Cucumber_Pseudomonas

4.15 Symptomsofbacterialwiltofeggplant(n.d.).InMissouriBotanicalGarden,Retrievedhttp://www.missouribo-tanicalgarden.org/Portals/0/Gardening/Gardening%20Help/images/Pests/Bacterial_Wilt_of_Cucumber879.jpg

4.16 Symptomsofchillinginjuryincucumber(n.d.). InNorthCarolinaCooperative,Retrievedhttp://www.ces.ncsu.edu/depts/pp/notes/Vegetable/vg1/ethanol.jpg

4.17 Symptomsofcucumber,whenitisstoredwithethyleneproducingfruitsliketomatoandpepper(n.d.)InNorthCarolinaCooperative,Retrievedhttp://www.ces.ncsu.edu/depts/pp/notes/Vegetable/vg1ethanol.jpg

5.1 Symptomsofclubrootincabbage(n.d.).InTheBikingGardener:NewPlants,Retrievedhttps://thebikinggarden-er.files.wordpress.com/2013/11/cabbage-clubroot.jpg

5.2 Symptomsofdowneymildewoncabbage(n.d.).InVegetablePathology–LongIslandHorticulturalResearch&Ex-tensionCenter,Retrievedhttp://www.longislandhort.cornell.edu/vegpath/photos/images/dm_cabbage2x1200.jpg

5.3 Symptomsofalternarialeafsot(n.d.).InWikimediaCommons,Retrievedhttps://commons.wikimedia.org/wiki/File:Alternaria_brassicae_(Berk.)_Sacc._Symptoms_on_cabbage.JPG

5.4 Symptomsofcabbageblackleg(PhomaStemCanker)(n.d.).OSUExtensionPlantPathology,Retrievedhttp://pnwhandbooks.org/plantdisease/cabbage-and-cauliflower-brassica-sp-black-leg-phoma-stem-canker

5.5 Symptomsoffusariumwiltincabbage(n.d.)InOntarioCropIPM,Retrievedhttp://www.omafra.gov.on.ca/IPM/english/brassicas/diseases-and-disorders/fusarium-wilt.html

5.6 Symptomsofgraymold in cabbage (n.d.)AuthorGeoffDixonRetrievedhttp://www.hortweek.com/pest-dis-ease-management-grey-mould-alert-prevent-damage/plant-health/article/1320777

5.7 Symptoms of white rust in cabbage (n.d). In Flicker, Retrieved https://www.flickr.com/photos/scotnel-son/15498990280

5.8 Symptomsofrhizoctoniaincabbage(n.d.)InDepartmentsofAgricultureandFoodAustralia,Retrievedhttps://www.agric.wa.gov.au/broccoli/diseases-vegetable-brassicas?page=0%2C1

5.9 Symptomsofsclerotiniawhiterotincabbage(n.d.)InDepartmentsofAgricultureandFoodAustralia,Retrievedhttps://www.agric.wa.gov.au/broccoli/diseases-vegetable-brassicas?page=0%2C1

5.10 Symptomsofcauliflowermosaicvirus(n.d.)InDepartmentsofAgricultureandFoodAustralia,Retrievedhttps://www.agric.wa.gov.au/canola/virus-diseases-vegetable-brassica-crops

5.11 Symptomsofbacterialsoftrot(n.d.)InPlantDiseaseandInsectClinic,Retrievedhttp://ncsupdicblog.blogspot.com/2012_04_01_archive.html

5.12 Symptomofblackrotoncabbage(n.d.).InCornellUniversityCollegeofAgricultureandLifeSciences,Retrievedhttp://www.longislandhort.cornell.edu/vegpath/photos/blackrotcabbage.htm

6.1 Symptomsofanthracnoseontomato(n.d.).AuthorBruceWatt,Retrievedhttp://extension.umaine.edu/ipm/ipd-dl/plant-disease-images/anthracnose-of-tomato-disease-images

6.2 Symptomsofearlyblightonleaf(n.d.).InCornellUniversity,Retrievedhttp://www.longislandhort.cornell.edu/vegpath/photos/early_blight.htm


6.3 Symptomsofleafmold(n.d.). InCornellUniversity,Retrievedhttp://www.longislandhort.cornell.edu/vegpath/photos/leafmold_tomato.html

6.4 Symptomsofblightontomato(n.d.).InGardeningKnowHow,Retrievedhttp://www.gardeningknowhow.com/wp-content/uploads/2010/10/tomato-blight1.jpg

6.5 Symptoms of verticilium wilt on tomato leaves (n.d.). In Tatoo Pictures, Retrieved http://4.bp.blogspot.com/-5cGxDfay4ME/UATkgsp0v2I/AAAAAAAACKs/F92pIz2xRBc/s1600/100_3382.JPG

6.6 Symptomsoflateblightontomato(n.d.).AuthorBobMulrooney,Retrievedhttp://agdev.anr.udel.edu/weekly-cropupdate/?tag=tomato&paged=4

6.7 Symptomsoffusariumwiltontomatoplant.(n.d.)InDemoGardenPlots,Retrievedhttps://thedemogardenblog.files.wordpress.com/2009/07/july-16-019.jpg

6.8 SymptomsofseptoriaontomatolLeaf(n.d.).InCornellUniversity,Retrievedwww.longislandhort.cornell.edu

6.9 Symptoms of powderymildewon tomato (n.d.). In Cornell University, Retrieved http://livegpath.cals.cornell.edu/?s=tomato+powdery+mildew&btnG=go&sitesearch=thissite

6.10 Symptomsofseedlingdampingoff(n.d.).InThoughtyomayskPictures,Retrievedhttp://www.thoughtyouma-yask.com/picsbtqq/tomato-seedlings-damping-off-disease

6.11 Symptomsofrhizopusrot(n.d.).AuthorR.Stolonifer,Retrievedhttp://postharvest.ucdavis.edu/pfvegetable/To-matoPhotos/?repository=30012&a=83743

6.12 Symptoms of ToMv on tomato (n.d.). In Technico Agricola, retrieved http://www.tecnicoagricola.es/el-vi-rus-del-mosaico-del-tomate-tomato-mosaic-virus-tomv/

6.13 SymptomsofINSVontomatoes(n.d.).InThoughtyomayskPictures,Retrievedhttp://www.thoughtyoumayask.com/picsbtqq/tomato-viral-disease

6.14 Symptomsofstolburontomato(n.d.).InPhytoplasmasDataBase,Retrievedhttp://www.q-bank.eu/Phytoplasmas/

6.15 Symptomsofbacterialcankerontomato(n.d.).AuthorT.AZitter,Retrievedhttp://vegetablemdonline.ppath.cor-nell.edu/PhotoPages/Impt_Diseases/Tomato/Tom_Bac.htm

6.16 Symptomsofbacterialwiltintomatoplant(n.d.).InInvasiveOrganization,Retrievedwww.invasive.org

6.17 Symptomsofbacterialspotontomato(n.d.).InPlazaEducation,Retrievedhttp://plaza.ufl.edu/jbjones/joneslab/bacterial_spot_of_tomato.htm

6.18 Symptomsofblossomendrotoftomato(n.d.).NewyorkStateUniversity,Retrievedhttp://www.ces.ncsu.edu/wp-content/uploads/2014/07/BlossomEndRotTomatoes.jpg

6.19 Symptomsofcatfaceintomato(n.d.).InGardeningKnow-How,Retrievedhttp://www.gardeningknowhow.com/wp-content/uploads/2013/09/tomato-catfacing.jpg

6.20 Symptomsofyellowshouldersintomato(n.d.).Ineorganics,retrievedhttp://eorganic.info/sites/eorganic.info/files/u86/yellow_Shoulder_5.jpg

7.1 Symptomsofphomarostrupii(n.d.).InWikiGardener,retrievedhttp://gardener.wikia.com/wiki/Phomarostrupii

7.2 Symptomsofblackcarrotrootdieback(n.d.).InWikiGardener,retrievedhttp://gardener.wikia.com/wiki/Black_rot_(carrot)

7.3 Symptomsofcottonyrot(n.d.).InWikiGardener,Retrievedhttp://gardener.wikia.com/wiki/Sclerotinia_rot

7.4 Symptomsofgraymoldrot(n.d.).InIntegratedPestManagement:RPDNo.942,Retrievedhttp://ipm.illinois.edu/diseases/series900/rpd942/

7.5 Symptomsofcraterrot(n.d.)AuthorEdwards,Don,Retrievedhttp://postharvest.ucdavis.edu/pfvegetable/Car-rotPhotos/?repository=29895

7.6 Symptomsofcarrotdiseasesfusariumrot(n.d.).InAgriculturalAdaptationCouncil,Retrievedhttp://archive.con-stantcontact.com/fs124/1103447516061/archive/1115104648661.html

7.7 Symptomsofcarrotred leafvirus (n.d.). Indpvweb,Retrievedhttp://www.dpvweb.net/dpv/showfig.php?dpv-no=249&figno=01

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7.8 Symptomsofparsnipyellowfleckvirus(n.d.).Indpvweb,Retrievedhttp://www.dpvweb.net/dpv/showfig.php?d-pvno=394&figno=04

7.9 Symptoms of bacterial soft rot (n.d.). In Departments of Agriculture and Food, Retrieved https://www.agric.wa.gov.au/carrots/minimising-postharvest-losses-carrots?page=0%2C1

7.10 Symptomsof bacterial leaf blight (n.d.). InTheCenter for Agriculture, Food and the Environment, Retrievedhttp://ag.umass.edu/fact-sheets/carrot-bacterial-leaf-blight

7.11 Symptomsofmisshapencarrotroots(n.d.). InTheVegetableCropsResearchUnit,Retrievedhttp://www.vcru.wisc.edu/simonlab/sdata/pimages/vegetableumbelliferae/Fig.%204.6.jpg

8.1 Symptomsofearlyblightinpepper(n.d.). InPlantandPestAdvisory,Retrievedhttp://plant-pest-advisory.rut-gers.edu/pepper-EarlyBlight-being-reported

8.2 Symptomsofpepperanthracnose(n.d.).InPlantandPestAdvisory,Retrievedhttp://plant-pest-advisory.rutgers.edu/pepper-anthracnose-being-reported/

8.3 Symptomsoffusariumwiltinpepper(n.d.).InDisease-PepperandEggplant,Retrievedhttp://www.semena.org/agro/diseases4/fusarium-wilt-e.htm

8.4 Symptomsofgraymold,(n.d.).AuthorD.Maes,Retrievedhttp://www.hawaiiplantdisease.net/glossary/images

8.5 Symptomsoffruitrotandsteamlesions(n.d.).InMichiganStateUniversity,Retrievedhttp://msue.anr.msu.edu/news/managing_phytophthora_on_pepper

8.6 Symptomsofpepperverticiliumwilt (n.d.). InOntarioCrop IPM, retrievedhttp://www.omafra.gov.on.ca/IPM/english/peppers/diseases-and-disorders/verticillium-wilt.html

8.7 Symptomsofcercosporaleafspot(n.d.).AuthorMatthewOrwat.Retrieved,http://franklin.ifas.ufl.edu/newslet-ters/tag/fungal/

8.8 Symptomsofpowderymildewonpepperleaves(n.d.).InFeedingKnowledgeOrganization,Retrievedhttps://www.feedingknowledge.net/02

8.9 Symptomsofphytopthorablightinpepper(n.d.).InFeedingKnowledgeOrganization,retrievedhttps://www.feedingknowledge.net/027

8.10 Symptoms of stolbur in pepper (n.d.) In Phytoplasmas and Pyroplasmas, Retrieved http://web2.mendelu.cz/af_291_projekty2/vseo/stranka.php?kod=472

8.11 Symptomsofcucumbermosaicviruson leaves (n.d.). InPictureSourceCrocus,Retrievedhttp://blogs.crocus.co.uk/kitchengarden/2009/08/01/68/

8.12 Symptomsofalfalfamosaicvirusinpepper(n.d.).InCornellUniversity,Retrievedhttp://www.cornell.edu/search/Alfalfa Mosaic virus. nd

8.13 Symptomsofbacterialeafspot(n.d.).InPlantPestAdvisory,Retrievedhttp://769/2014/07/30/july-30-2014-man-aging-pepper-bacterial-spot/

8.14 Symptomsofbacterialcankeronleaves(n.d.). InOhioStateUniversity,Retrievedhttp://u.osu.edu/miller.769/files/2014/07/PepperCanker-1-slua8w.jpg

8.15 Symptomsofbacterialwiltonpepperstem(n.d.)InHawaiiPlantDiseases,Retrievedhttp://www.hawaiiplantdis-ease.net/glossary/images/Bacterial_wilt/Bacterial%20wilt3.jpg

9.1 Symptomsofblackleginbeet(n.d.)InNewyork’sFoodandLifeSciencesBulletin,Retrievedhttp://vegetablem-donline.ppath.cornell.edu/factsheets/Beet_RootRot.htm

9.2 Symptomsofcercosporaleafspotofbeets(n.d.)InTheCenterforAgriculture,FoodandtheEnvironmentattheUniversity of Massachusetts, Retrieved https://ag.umass.edu/fact-sheets/cercospora-leaf-spot-of-swiss-chard-beets-spinach

9.3 Symptomsofdownymildew(2006).AuthorMelodiePutnam.Retrievedhttp://pnwhandbooks.org/plantdisease/node/3982/print

9.4 Symptomsofbeet rust (n.d.). InRheinischeFriedrich-Wilhelms-UniversitätBonn,Retrievedhttp://www.preci-sion-crop-protection.uni-bonn.de/gk_research/project_3_05/image_1.jpg


9.5 Symptomsofbeetrootgraymold(n.d.).InTheAgroAtlas,Retrievedhttp://www.agroatlas.ru/en/content/diseas-es/Beta_alba/Beta_alba_Botrytis_spp/

9.6 Symptomsofbeetpowderymildew(n.d.).AuthorHowardFSchwartz,Retrievedhttp://www.forestryimages.org/browse/detail.cfm?imgnum=5357587

9.7 Symptomsofbeetmosaicvirus(n.d.).AuthorsC.M.RushandG.B.Heide,Retrievedhttp://www.apsnet.org/pub-lications/imageresources/Pages/1-06.aspx

9.8 Symptomsofbeetcurlytopvirus(2013).AuthorHowardF.Schwartz,Retrievedhttps://commons.wikimedia.org/wiki/File:Beet_curly_top_virus_geminiviridae_common_bean.jpg

9.9 Symptomsofcrowngall(n.d.).InKWSUK-ProductPortfolio,Retrievedhttps://www.kws-uk.com/aw/KWS/unit-ed-kingdom/Products-TopMenu/Sugar-beet/Technical-Reference-Folder/Diseases/Artikel-Krankh-GB/~biwd/Image-gallery-of-Diseases/

9.10 Symptomsoftuberculosisofbeet(n.d.).InAgro-Atlas,Retrievedhttp://www.agroatlas.ru/en/content/diseases/Beta_alba/Beta_alba_Xanthomonas_beticola/

9.11 Symptomsofbeetrootzoning(n.d).InGardeningCornellUniversity,Retrievedhttp://www.gardening.cornell.edu/homegardening/scene18f3.html

10.1 Symptomsofdowneymildewinonion(n.d.).InPlantesygdomme,Retrievedhttp://www.plantesygdomme.dk/loegskimmel/target13.html

10.2 Symptomsofleekrust(n.d.).InNagaNegi,Retrievedhttp://www.namayasai.co.uk/Negi.htm

10.3 Symptoms of neck rot of garlic (n.d.). In Plant DiseasesManagement Handbook,Midwest, Retrieved http://pnwhandbooks.org/plantdisease/node?page=266

10.4 Symptomsofalternariablightinleaves(n.d.).InInformationforCommercialVegetableProductioninOntario,Retrievedhttp://onvegetables.com/2012/07/06/update-on-stemphylium-leaf-blight-of-onions-in-ontario/

10.5 Symptomsofneckrotinonion(n.d.).InWikiGardner,Retrievedhttp://gardener.wikia.com/wiki/OnionNeck_rot

10.6 Symptomsofonionsmut(n.d.).InWikiGardner,retrievedhttp://gardener.wikia.com/wiki/Onion_Smut

10.7 Symptomsoffusariumwiltononion(n.d.)InWikiGardner,Retrievedhttp://gardener.wikia.com/wiki/Fusarium_basal_rot

10.8 Symptomsofwhiterotofonion(n.d).InWikiGardener,retrievedhttp://gardener.wikia.com/wiki/white

10.9 Symptomofblackmoldofonion(n.d.).AuthorPaulCowan,Retrievedhttp://www.123rf.com/photo_832375_an-onion-with-a-severe-infestation-of-black-mold-aspergillus-niger-a-fungal-disease-most-commonly-th.html

10.10 Onionmosaicvirus(n.d.).AuthorPaulCowan.Retrievedhttp://www.123rf.com/photo_832375_an-onion-with-a-severe-infestation-ofMosaicvirus.html

10.11 Symptoms of bacterial soft rot in onion (n.d.). In Keith Foster Blog, Retrieved https://keithfoster.wordpress.com/2011/05/24/ian-paton-onions-update/

11.1 Symptomsofwhitemoldonwatermelon(n.d.).InUniversityofDelaware,Retrievedhttp://extension.udel.edu/weeklycropupdate/

11.2 Symptomsofanthracnoselesionsonwatermelonfruit(n.d.).InPurdueUniversity,Retrievedhttps://ag.purdue.edu/arp/swpap/VeggieDiseasesBlog/Lists/Posts/Post.aspx?ID=19

11.3 Symptomsofdowneymildewinwatermelonfruitandleaves(n.d.).InBrooksCountryAgConnection,Retrievedhttps://blog.extension.uga.edu/brooksag/2014/06/vegetable-alerts/

11.4 Symptomsof powderypildewon leaves (n.d.). InTélédétection et SIG en agriculture, Retrievedhttp://www.seos-project.eu/modules/agriculture/agriculture-c08-p01.fr.html

11.5 SymptomsofWwatermelonmosaicvirus(n.d.).InEphytiaInra,Retrievedhttp://ephytia.inra.fr/fr/D/1668

11.6 SymptomsofCMVonwatermelonnewgrowth(n.d.).AuthorGBrust,Retrievedhttp://agdev.anr.udel.edu/week-lycropupdate/?p=2239

11.7 Symptomofbacterialfruitblotchinwatermelonfruit(n.d.).AuthorE.Lookabaugh.Retrievedhttp://ncsupdic-blog.blogspot.com/2012/07/bacterial-fruit-blotch-of-watermelon.html

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11.8 Symptomsofblossomendrotofwatermelon(n.d.).InMinnesotaMinistryofAgriculture,Retrievedhttp://www.omafra.gov.on.ca/IPM/images/cucurbit/disorders/blossom-end-rot/blossom-end-rot-1_zoom.jpg

12.1 Symptomsofpowderymildewinmelons(n.d.).InSpecialtyCropportunities,Retrievedhttp://www.omafra.gov.on.ca/CropOp/en/spec_veg/cucurbits/mouse.html

12.2 Symptomsoffusariumwilt(n.d.).InSpecialtyCropportunities,Retrievedhttp://www.omafra.gov.on.ca/IPM/en-glish/cucurbits/diseases-and-disorders/fusarium-wilt.html

12.3 Symptomsofanthracnoseinmelons(n.d.).AuthorThomas.A.Zitter,Retrievedhttp://vegetablemdonline.ppath.cornell.edu/DiagnosticKeys/CucurLeaf/Anthrac/Anth_mel.htm

12.4 Symptomsofdowneymildew inmelons (n.d.). InOntarioMinistryofAgriculture,FoodandRuralAffairs,Re-trievedhttp://www.omafra.gov.on.ca/english/crops/facts/10-065.htm

12.5 Symptomsofcucumbermosaicvirus(n.d.).AuthorThomasA.Zitter,Retrievedhttp://www.apsnet.org/edcenter/intropp/lessons/viruses/Pages/Cucumbermosaic.aspx

12.6 Symptomsofwatermelonmosaicvirus(n.d.). InCaliforniaAgriculture,Retrievedhttp://ucce.ucdavis.edu/files/repository/calag/img4903p22a.jpg

12.7 Symptomsofbacterialfruitblotch(n.d.).AuthorDavidB.Langston,Retrievedhttp://wiki.bugwood.org/Acidovo-rax_avenae_pv._citrulli

12.8 Symptomsofangularleafspot(n.d.).InMinistryofAgricultureBarbados,Retrievedhttp://www.agriculture.gov.bb/agri/index.php?option=com_content&view=article&id=431:angular-leaf-spot&catid=148:plant-protection&Itemid=99

13.1 Molecricket(n.d.).InWikipedia,Retrievedhttps://en.wikipedia.org/wiki/Mole_cricket#/media/File:Mole_cricket02.jpg

13.2 Pictureofclickbeetles(n.d.).InCornInsectandDiseaseGuide,Retrievedhttps://www.pioneer.com/home/site/us/agronomy/crop-management/corn-insect-disease/wireworm/

13.3 Root-knot nematode (n.d.). In Edible San Marcos, Retrieved https://ediblesanmarcos.wordpress.com/root-knot-nematode/

13.4 Potatorotnematode(n.d.).InTheResourcefortheGlobalPotatoIndustry,Retrievedhttp://www.potatopro.com/news/2011/potato-rot-nematode-confirmed-ontario

13.5 Coloradopotatobeetle (n.d.) InWikipedia,Retrievedhttps://en.wikipedia.org/wiki/Colorado_potato_beetle#/media/File:Colorado_potato_beetle.jpg

13.6 Aphisgossypii(n.d.).InGestiónIntegradadePlagasyEnfermedadesenCítricos,Retrievedhttp://gipcitricos.ivia.es/area/plagas-principales/pulgones/pulgon-del-algodon

13.7 Blackbeanaphid(n.d.).InWikipedia,Retrievedhttps://en.wikipedia.org/wiki/Black_bean_aphid

13.8 Cabbageaphidsoncurlykale(2007).AuthorRasbak,Retrievedhttps://commons.wikimedia.org/wiki/File:Brevic-oryne_brassicae_on_curley_kale_(Melige_koolluis_op_boerenkool).jpg

13.9 Pictureofredcabbagebug(2007).AuthorLuisFernandezGarcia,Retrievedhttps://commons.wikimedia.org/wiki/File:Eurydema-ornatum-Madrid.jpg

13.10 Pictureofcarminemite(n.d.).InTurbosQuid,Retrievedhttp://www.turbosquid.com/3d-models/tetranychus-tel-arius-3ds/568746

13.11 Dry bulbmite (n.d.) InWeekly CropUpdate, Retrieved http://agdev.anr.udel.edu/weeklycropupdate/wp-con-tent/uploads/2012/05/bulbmite1b.jpg

13.12 Bulbmite(n.d.).InMacroid.ru,Retrievedhttp://macroid.ru/showphoto.php?photo=62142

13.13 Picture of red spider mite (n.d.). In PROGilles San Martin, Retrieved https://www.flickr.com/photos/sanmar-tin/4883560779

13.14 Tomato(andhemp)russetmite(n.d.).InEverwoodfarm,Retrievedhttp://www.everwoodfarm.com/Pest_Insect_Cross_Listing/Help_with_Russet_Cyclamen_and_Broad_Mites

13.15 Greenhousewhitefly (n.d.). InWeißeFliege,Retrievedhttps://www.google.com/search?q=Trialeurodes+vapo-rariorum&client=opera&hs=4IR&tbm=isch&source=lnt&tbs=isz:l&sa=X&ved=0CBMQpwVqFQoTCIiWns3yt8c-CFUUKLAodKRMKlw&dpr=1&biw=1366&bih=669#imgrc=2H-fUmdZn8a-sM%3A


13.16 Onionthrips(n.d.).InCenterforInsectBioinformatics,Retrievedhttp://www.nabg-nbaii.res.in/insectinfo/details.php?nbaiiuid=INI078A

13.17 Crucifer flea beetle (n.d.). In Crucifer Flea Beetle, Retrieved http://fieldcropnews.com/wp-content/up-loads/2013/06/Crucifer-Flea-beetle.jpg

13.18 Turnipsawfly-Athaliarosae(n.d.).InNatureSpot,Retrievedhttp://www.naturespot.org.uk/species/turnip-saw-fly

13.19 Diamond-back moth (n.d.). InWikimedia Commons, Retrieved https://upload.wikimedia.org/wikipedia/com-mons/2/29/Plutella.maculipennis.mounted.jpg

13.20 Cabbagewhite(Cabbagebutterfly)(n.d.). InWikimediaCommons,Retrievedhttps://commons.wikimedia.org/wiki/Pieris_brassicae#/media/File:Pieris.brassicae.caterpillar.jpg

13.21 Cabbage moth. Author Olaf Lenninger. Retrieved https://commons.wikimedia.org/wiki/File:Mamestra.brassi-cae.7460.jpg

13.22 Cabbage maggot—Delia radicum (n.d.) In Maine. Gov, Retrieved http://www.maine.gov/dacf/php/gotpests/bugs/images/cabbage-maggot/cm-larva-big.jpg

13.23 Cabbagestemweevil(n.d.).AuthorDavid’yanG.E,Retrievedhttp://www.agroatlas.ru/en/content/pests/Ceuto-rhynchus_pallidactylus/

13.24 Onionmaggot (n.d.). In Plantvillage, Retrievedhttps://www.plantvillage.com/en/topics/onion/infos/diseases_and_pests_description_uses_propagation

13.25 Carrotrustfly(n.d.).InAgroatlas,Retrievedhttp://www.agroatlas.ru/en/content/pests/Psila_rosae/

13.26 Carrot psyllid (n.d.). Author Joe Botting, Retrieved http://www.britishbugs.org.uk/homoptera/Psylloidea/Trio-za_apicalis.html

13.27 Beetweevil(n.d.).InZin.Ru,Retrievedhttp://www.zin.ru/Animalia/Coleoptera/images/w_800/IMG_4959.JPG

13.28 Beet leafminer (n.d.). In Wikipedia, Retrieved https://en.wikipedia.org/wiki/Pegomya_hyoscyami#/media/File:Spinach_leafminer_(adult).jpg

13.29 Beetcaspidbug(n.d.).InAgroatlas,Retrievedhttp://www.agroatlas.ru/en/content/pests/Polymerus_cognatus/

13.30 Beet tortoise (tortoisebeetle) (n.d.). InWikipedia,Retrievedhttps://en.wikipedia.org/wiki/Cassida_nebulosa#/media/File:Chrysomelidae_-_Cassida_nebulosa.JPG

13.31 Potato tubermoth (n.d.). InMicrolepidoptera on Solanaceae, Retrieved http://idtools.org/id/leps/micro/fact-sheet.php?name=<em>Phthorimaea+operculella<%2Fem

206 ბოსტნეული და ბაღჩეული კულტურების ძირითადი მავნებელ-დაავადებები და მათ წინააღმდეგ ბრძოლა საქართველოში

identification and control of€¦ · remain the same genetically. during sexual reproduction,...

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