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57Pesticide Safety Education Program, Ohio State University Extension

Fruit andVegetable

Crops

CATEGORY 3

60 Pesticide Safety Education Program, Ohio State University Extension

New products:• Omega 500F (fluazinam) is primarily a fungicide but it also kills spider mites, for use on apples (28-day

PHI). Made by Syngenta.Products with re-established registration:

• Closer SC (sulfoxaflor, in IRAC group 4C, the sulfoximines): registration reestablished 10/14/2016. Was registered May 2013, use was suspended in Sept. 2015, all uses cancelled on 11/12/2015. Now for use on pome fruit, stone fruit, grapes, brassica vegetables, fruiting vegetables, leafy vegetables, leaves of root and tuber crops, for control of plant bugs, aphids, leafhoppers, whiteflies. Former label had strawberries and cucurbits but these are not on the new label. Can not be used until after petal-fall on fruit crops. Made by Dow.

• Transform WG (sulfoxaflor): registration reestablished 10/14/2016. Had been registered May 2013, but use was suspended in Sept. 2015, then all uses cancelled on 11/12/2015. For use on potatoes, root and tuber crops (radish, celeriac, beet, carrot), and beans, for control of aphids, leafhoppers, plant bugs, whiteflies. Made by Dow.

Products with registration expanded to additional crops:• Sivanto Prime (flupyradifurone, in IRAC group 4D; 1.67 lb AI/gal): foliar use will be allowed on stone fruit

and caneberries. Soil application will be allowed on Brassica crops and leafy vegetables. From Bayer. Announced September 2016; new label not yet available but coming in 2017.

Product consolidations or renamings:• Sivanto Prime (flupyradifurone, in IRAC group 4D; 1.67 lb AI/gal) has replaced Sivanto 200SL (1.67 lb

AI/gal), for systemic control of leafhoppers, aphids, whiteflies, squash bug, potato beetle, thrips, pear psylla, San Jose scale, blueberry maggot, mealybug on apples, pears, grape, blueberry, strawberry, Brassicas, cucurbits, fruiting veg, leafy veg, legumes, root veg, tuber/corm veg, hops. From Bayer. Registered January 2015. Stone fruit and caneberries added Sept. 2016.

• Portal XLO (0.4EC) has replaced Portal (0.4EC). For control of two-spotted spider mite, European red mite, broad mite, cyclamen mite, tomato russet mite, pear rust mite, pear psylla, leafhoppers, whiteflies. Peaches, potato, beans, and cucumbers are now on main label, no longer on supplemental labels. Also for use on pome fruit, grapes, strawberries, hops, fruiting veg, melons, mint. Made by Nichino.

Registration cancellations or deletions:• Belt SC (flubendiamide) and the former Synapse WG (flubendiamide), made by Dow, and Tourismo

(flubendiamide + buprofezin), made by Nichino: cancelled August 2016. Distributors allowed to sell remaining inventory. Growers permitted to use product consistent with label use directions.

• Thionex, Thiodan (endosulfan): No longer for use on any crop; final use allowed was strawberries (perennial) which ended on 7/31/2016. Uses on all other crops have been phased out over the previous 4 years. Take all remaining product to ODA organized pesticide disposal collection site.

• Calypso 4F (thiacloprid): voluntary cancellation was announced by Bayer on 12/13/2013; State registrations are being phased out; is still registered in Ohio for 2017.

• Carzol SP (formetanate hydrochloride) is being deleted from our spray guides; its use now restricted to nectarines in the Pacific NW.

• Applaud (buprofezin), an insect growth regulator, is being deleted from our spray guide for grapes; it still exists but not registered in Ohio or most other northern States. Made by Nichino America.

• Courier SC (buprofezin), an insect growth regulator, is being deleted from our spray guides; it still exists and is registered in Ohio but not in most other northern States that share our spray guide. For use on strawberries, beans, Brassica, cucurbits, fruiting veg., leafy veg. Made by Nichino America.

New pests: no pests brand new to Ohio this year, but three continue to spread to new areas within Ohio:• Spotted wing drosophila: on raspberries, blackberries, blueberries. Small worms in ripening fruit.• Brown marmorated stink bug: on peach, apple, raspberry, sweet corn, pepper, tomato. Causes

blotches on surface of fruit and corky brown tissue beneath surface; deforms kernels, seeds.• Western bean cutworm: on sweet corn. Similar to corn earworm but with many worms per ear.

Old pests: • Two-spotted spider mite: causing problems on many crops. See summary of miticide choices.

Vegetable & Fruit Insecticide News for 2016-2017Celeste Welty

Department of Entomology, Ohio State University Extension


Summary of Vegetable & Fruit Insecticide Changes, 2011-2015 (not including pre-mixes)

NEW REGISTRATIONS:sweet corn

(none)tomato, pepper, & eggplant

Closer (5/2013; 10/2016)Sivanto (1/2015)Exirel (1/2014)Verimark (1/2014)

tomato onlyNealta (1/2014)

cucurbitsSivanto (1/2015)Exirel (1/2014)Verimark (1/2014)

Brassica head, stem & leafyCloser (5/2013; 10/2016)Hero (10/2015)Sivanto (1/2015)Exirel (1/2014)Verimark (1/2014)

beans & peasSivanto (1/2015)

beans onlyTransform (5/2013; 10/2016)

root veg (radish, beets, carrot) Transform (5/2013; 10/2016)Sivanto (1/2015)

potato Transform (5/2013; 10/2016)Sivanto (1/2015)Torac (1/2014)Verimark (1/2014)

onionsExirel (1/2014)Movento (2013)Scorpion (2013)Venom (2012)

lettuces, endive, spinach, parsley (leafy veg.)Closer (5/2013; 10/2016)Sivanto (1/2015)Torac (1/2014)Exirel (1/2014)Verimark (1/2014)

herbs and/or mints(none)

asparagus(none)

strawberries Sivanto (1/2015)Nealta (1/2014)Beleaf (2013)

brambles /caneberriesSivanto (9/2016)

blueberriesSivanto (1/2015)Exirel (1/2014)

grapesCloser (5/2013; 10/2016)Sivanto (1/2015)Nealta (1/2014)Scorpion (2013)

apples & pearsCloser (5/2013; 10/2016)Sivanto (1/2015)Nealta (1/2014)Exirel (1/2014)Madex HP (8/2013)

peach, plum, & cherryCloser (5/2013; 10/2016)Sivanto (9/2016)Apta (4/2014)Exirel (1/2014)Madex HP (4/2013)Portal (2013)Calypso (4/2013)Scorpion (2013)Venom (2012)

CANCELLATIONS:pome fruit, stone fruit, grape, strawberry, sweet corn, Brassica, fruiting veg, leafy veg, legume veg, cucurbits

Belt (8/2016)pome fruit, stone fruit, grape

Tourismo (8/2016)strawberry (perennial)

Endosulfan, Thionex (7/31/2016)

cucurbits, strawberriesCloser (11/2015)

apple, blueberry, pepper, potato, pumpkin, sweet corn, tomato, winter squash


apple, pear, cherry, parsleyGuthion (9/30/2013)

pear Endosulfan, Thionex (7/31/2013)

peach, plum, cherry, strawberry (annual), cabbage, kale, cukes, melons, summer squash, lettuce



Summary of products for control of spider mites. Table 1: fruit crops and hops. Table 2: vegetable crops.

Table 1. Products for spider mite control on specified fruit crops and hops.Product name & common name

Use Pre-harvest interval, by cropHops Straw-

berryBrambles Blueber-

ryGrape Apple Peach

Acramite 50WS or 4SC (bifenazate)

general 14 days 1 day 1 day not registered

14 days 7 days 3 days

Apollo (clofentezine) general not registered

not registered

not registered

not registered


Envidor (spirodiclofen) general 14 days not registered

not registered

not registered


Kanemite (acequinocyl) general 7 days not registered

not registered

not registered

not registered

14 days not registered

Nealta (cyflumetofen) general not registered

1 day not registered

not registered

14 days 7 days not registered

Nexter (pyridaben) general not registered

not registered

not registered

not registered


Onager (hexythiazox) general not registered

not registered

not registered

not registered


Portal 0.4EC or FujiMite 5EC (fenpyroximate)

general 15 days 1 day not registered

not registered


Savey (hexythiazox) general up to burr 3 days 3 days not registered

not registered

28 days 28 days

Zeal 72WDG or 72WSP (etoxazole)

general 7 days 1 day 0 days not registered


Agri-Mek 0.7 SC or 0.15EC (abamectin)

restricted 28 days 3 days 7 days not registered


MSR (Metasystox-R) 2EC (oxydemeton-methyl)

restricted not registered

not registered

not registered

not registered

non-bearing only

non-bearing only

non-bearing only

Vydate L 2WSL (oxamyl) restricted not registered

not registered

not registered

not registered

not registered

14 days non-bearing only

- Celeste Welty, Extension Entomologist, Ohio State University, 7/28/2016.


Table 2. Products for spider mite control on specified vegetable crops.

Product name & common name

Use Pre-harvest interval, by cropBeans Melons Cucum-

bersSquash, pump-kins

Tomato Pepper Egg-plant

Sweet corn

Acramite 50WS or 4SC (bifenazate)

general 3 days 3 days 3 days 3 days 3 days 3 days 3 days not registered

Dimethoate 4EC (dimethoate)

general; not in green-house

0 days 3 daysa not registered

not registered

7 daysa 0 daysa not registered

not registered

Dicofol 4E (dicofol) general 21 days not registered

2 days 2 days 2 days 2 days not registered

not registered

Oberon 2SC (spi-romesifen)

general not registered

7 days 7 days 7 days 1 day 1 day 1 day 5 days

Onager (hexythiazox) general not registered

not registered

not registered

not registered

1 day (green-house)

1 day 1 day not registered

Portal 0.4EC or FujiMite 5EC (fenpy-roximate)

general 1 day 3 days 1 day not registered

1 day 1 day 1 day not registered

Zeal 72WDG or 72WSP (etoxazole)

general not registered

7 days 7 days 7 days not registered

not registered

not registered

not registered

Agri-Mek 0.7 SC or 0.15EC (abamectin)

restricted 7 days 7 days 7 days 7 days 7 daysb 7 days 7 days 7 days

MSR (Meta-systox-R) 2EC (oxydemeton-methyl)


14 days 14 days 14 days not registered

not registered

not registered

not registered

Vydate L 2WSL (oxamyl)


1 daya 1 daya 1 daya 3 daysa 7 daysa 1 day not registered

a Product registered for use on this crop but mites not on list of target pests for this crop, however mites listed as target pest on other crops.b 7 days outdoors, or 1 day for commercial greenhouse tomatoes.

- Celeste Welty, Extension Entomologist, Ohio State University, 7/28/2016.


Scab of AppleMelanie L. Lewis Ivey, Michael A. Ellis

Department of Plant Pathology, Ohio State University Extension

SCAB OF APPLE PLPATH-FRU-23

ohioline.osu.edu/factsheet/plpath-fru-23

College of Food, Agricultural, and Environmental Sciences, Department of Plant Pathology

Scab of AppleMelanie L. Lewis Ivey, Assistant Professor, Department of Plant Pathology, The Ohio State University-Ohio Agricultural Research and Development Center, Wooster, OH.Michael A. Ellis, Professor Emeritus, Department of Plant Pathology, The Ohio State University-Ohio Agricultural Research and Development Center, Wooster, OH.

DiseaseDevelopmentandSymptomsDiseasedevelopmentisfavoredbywet,coolweatherthatgenerallyoccursinspringandearlysummer.Thefungussurvivesthewinterondiseasedleavesthathavefallenunderthetreethepreviousyear.Inthespring,whenbudsarebeginningtodevelop,thefungusproducesmillionsofspores(ascospores).ThesesporesarereleasedintotheairduringrainyperiodsinApril,MayandJune.Theyarethencarriedbythewindtoyoungleaves,flowerpartsandfruitsandinfectionisinitiated.

Applescabisoneofthemostseriousdiseasesofappleworldwide.Inadditiontoapples,crabapplesandmountainasharealsosusceptibletoapplescabdisease.Applescabiscausedbythefungus,Venturia inaequalis.Boththeleavesandfruitcanbeaffected.Infectedleavesmaydropprematurelyresultinginunsightlytrees,withpoorfruitproduction.Thisearlydefoliationmayweakentreesandmakethemmoresusceptibletowinterinjuryorotherpests.Diseasedfruitsareblemishedandoftenseverelydeformedandmayalsodropearly.

Symptomsfirstappearasspots(lesions)onthelowerleafsurface,thesideoftheleafthatisfirstexposedtothefungalsporesasthebudsopen.Atfirst,thelesionsaresmall,velvety,olivegreenincolor,andhaveunclearmargins(Figure1-left).Onsomecrabapples,infectionsmaybereddishincolor. Thefungusproducesasecondtypeofspore(conidium)intheselesions. Thesesporesarecarriedandspreadbysplashingraintootherleavesandfruitsandnewinfectionsoccur. Asthespotsage,theinfectionsbecomedarkerwithmoredistinctmargins(Figure1-right).Lesionsmayappearmorenumerousclosertothemid-veinoftheleaf.Ifheavilyinfected,theleafbecomesdistortedanddropsearlyinthesummer.Treesofhighlysusceptiblevarietiesmaybeseverelydefoliatedbymidtolatesummer.

Figure1.Applescablesionsonappleleaves.

Figure2.Applescablesionsonfruit.


Scab of Apple—page 2

Apple Scab ManagementApplescabcanbesuccessfullymanagedbyintegratingresistantvarieties,culturalpractices,andchemicalorbiologicalcontrol.

Fruitsymptomsaresimilartothosefoundonleaves.However,themarginsofthespotsareoftenmoredistinctonthefruit(Figure2)thanontheleaves.Fruitmayalsobedeformed.

Applevarietieswithcompleteresistancetoscab

CrimsonCrispCrimsonGoldEnterpriseFreedomGalarinaGoldrushJonafreeLibertyNovaEasygro

NovamacPriscillaPristineRedfreeScarletPrimaSirPrizeSundanceWilliamsPride

Applevarietieswithmoderateresistancetoscab

Adam’sPermainAshmead’sKernelHaralsonHoney Crisp

NJ90SuncrispYellowTransparent

Applevarietieswithlowresistancetoscab

AkaneBelmacBritegoldFlorina(Querina)GrimesGoldenHoneyGoldMacfreeMoira

MurrayNovaSpyPaularedPinova (Corrail)RedfreeRunkelWolfRiver

Table1.Varietieswithresistancetoapplescab.


VarietyselectionPlantingresistantorscabimmuneapplevarietiesistheidealmethodformanagingscab.Backyardandorganicgrowersarestronglyencouragedtoplantresistantvarietiesinordertoreduceoreliminatetheneedforfungicideapplications.Therearenumerousapplevarietieswithcompleteresistanceormoderateresistancetoapplescab(Table1).Allothervarieties,includingmostcommerciallygrownvarietiesaresusceptibletoscab;however,theydifferintheirdegreeofsusceptibility.Scabresistantvarietiesvaryinsusceptibilitytoearly-seasondiseasesandallaresusceptibletosummerdiseases(J.Beckerman,BP-132-W).

CulturalpracticesRakeanddestroyfallenleavesbelowappleandcrabappletreesinthefall(Figure3).Thiswilldramaticallyreducethenumberofsporesthatcanstartthediseasecycle(Figure4)overagainthefollowingspring.Leavescanalsobechoppedwithamulchinglawnmowerorflailmowerbutthispracticeshouldbecoupledwithtwoorthreeapplicationsof5%ureatofallfoliage.Ureaapplicationsincreaseleafdecomposition.

Fornewplantings,selectasitethatgetsdirectsunforatleasteighthoursandspacetreessothataircanmoveeasilythroughthetreecanopiesandorchard.Treespacingwilldependonthetypeofappletree(dwarfvs.standard)andtrellisingsystem.Prunetreesyearlytoopenthecanopyandpromoteleafdrying.

Figure3.Fallenleavesshouldberakedandinthefalltoreducenewinfectionsinthespring.


ChemicalandbiologicalcontrolWhereresistancetoscabisnotpresent,theapplicationoffungicidesistheprimarymethodtomanageapplescab.Organicandbackyardgrowerscanusebiocontrolproductstosuppressdiseasedevelopmentbuttheseproductsshouldbeusedincombinationwithresistantvarietiestoachievemaximumcontrol.

Propertimingoffungicidesiscriticalforeffectivecontrolofapplescab.Applicationsshouldbeginearlyintheseasonwhenthefirstgreentipsbegintoemergeandcontinueona7- to10-dayschedulethroughouttheseason.Earlyapplicationswillreducethenumberofseasonalspraysneededtomanageapplescabandwillincreasefruitproductionandquality.CommercialgrowerscanconsulttheMidwestFruitPestManagementGuide (Bulletin506)forcurrentfungiciderecommendationsandsprayschedules.

Backyardgrowersarelimitedinthenumberofhighlyeffectivefungicidesavailableforapplescabmanagement.Mostoftheavailablefungicidesareprotectantsandwillneedtobeappliedafterheavyrains.ForcurrentfungiciderecommendationsbackyardgrowerscanconsulttheControllingDiseasesandInsectsinHomeFruitPlantings (Bulletin780)guide.BothguidescanbeobtainedfromyourcountyextensionofficeortheCFAESPublicationsonlinebookstoreatestore.osu-extension.org.

The College of Food, Agricultural, and Environmental Sciences and its academic and research departments including, Ohio Agricultural Research and Development Center (OARDC), Agricultural Technical Institute (ATI) and Ohio State University Extension embraces human diversity and is committed to ensuring that all research and related educational programs are available to clientele on a nondiscriminatory basis without regard to age, ancestry, color, disability, gender identity or expression, genetic information, HIV/AIDS status, military status, national origin, race, religion, sex, sexual orientation, or veteran status. This statement is in accordance with United States Civil Rights Laws and the USDA.

Bruce McPheron, Ph.D., Vice President for Agricultural Administration & Dean

For Deaf and Hard of Hearing, please contact the College of Food, Agricultural, and Environmental Sciences using your preferred communication (e-mail, relay services, or video relay services). Phone 1-800-750-0750 between 8 a.m. and 5 p.m. EST Monday through Friday. Inform the operator to dial 614-292-6891.

Copyright © 2014, The Ohio State University

Scab of Apple—page 3

Useful ReferencesBeckerman,J., Disease Susceptibility of Common Apple

Cultivars. Purdue Extension, BP-132-W

Figure4.Applescabdiseasecycle.ImagecourtesyofW.Wilcox,CornellUniversity,NYSAES,Geneva,NY.


Bitter Rot of AppleMelanie L. Lewis Ivey, Michael A. Ellis


PLPATH-FRU-20

DEPARTMENT OF PLANT PATHOLOGY

Bitter Rot of AppleMelanie L. Lewis Ivey, Assistant Professor, Department of Plant Pathology, The Ohio State University-Ohio Agricultural Research and Development Center, Wooster, OH.Michael A. Ellis, Professor Emeritus, Department of Plant Pathology, The Ohio State University-Ohio Agricultural Research and Development Center, Wooster, OH.

DiseaseDevelopmentandSymptomsDiseasedevelopmentisfavoredbyhightemperatures(80-90degreesF)andhighrelativehumidity(80-100%);thusthediseaseismostcommoninthesoutheasternUnitedStates.Thefungisurvivethewinterindeadwoodormummifiedfruitthatwereinfectedduringthepreviousseason.Inthespring,spores(conidiaand/orascospores)fromtheseoverwinteringsitesserveastheprimaryinoculumsourcefornewinfections.Conidiaarespreadbysplashingandwind-blownrain,insectsandbirdswhileascospores arereleasedintotheairduringrainyperiods.Fruitsaresusceptibletoinfectionsfrompetalfallthroughharvest.

Bitterrotisacommonfruitrottingdiseaseofapple(andpear)thatoccursinallstateswhereapplesandpearsaregrown(Figure1).Bitterrotiscausedbythefungi,Colletotrichum gloeosporiodes,C.acutatum andGlomerella cingulata.Colletotrichumgloeosporioides andC.acutatum arethesamepathogenicfungithatcauseanthracnosefruitrotonstrawberryandblueberry,riperotongrapeandanthracnosediseaseonpeach.Glomerella cingulatacanalsocausealeafspotandcankeronapple,althoughtheseformsofthediseasearenotcommoninOhio.

Symptomsfirstappearassmall,slightlysunkencircularareasthatarelighttodarkbrownincolor.Onmaturefruittheseareasmaybesurroundedbyaredhalo.Whenenvironmentalconditionsareoptimal,thespotscanenlargerapidlyandcovertheentirefruitsurface.Asthespotsenlarge,thefruitrotsymptomscanvarydependingonthefungalisolateandthetypeofsporethatinitiatesinfection.Spotsinitiatedfrombyisolatesthatonlyproduceconidia(referredtoasconidialisolates)aresunkenandcircularwithconcentricrings.Withintherings,copiousamountsofconidiaareproducedinfruitingbodiescalledacervuli (Figure2-Top).Undermoist,humidconditions,thesporemassesappearcreamyandaresalmontopinkincolor. Spotsinitiatedbyisolatesthatproduceconidiaandascospores (referredtoasperithecial isolates)areusuallynotsunkenandaredarkerbrownincolorthanspotsproducedbyconidialisolates(Figure2-Bottom).Withinthespots,structuresthatcontainascopsores (perithecia)forminblackclumpsoverthesurface.Figure1.Bitterrotonapplefruit.

Figure2.Close-upsofbitterrotonapplefruit.

Top- Sunkenlesioncontainingconcentricringsofacervuli.PhotocourtesyofJonClements,UmassAmherst.

Bottom- Darkcircularlesionwithbrownacervuliscatteredonthesurface.


Bitter Rot of Apple—page 2

Bitter Rot ManagementBitterrotcanbesuccessfullymanagedbyintegratinggoodsanitationpractices,culturalpracticesandchemicalcontrol.Therearenovarietiesthatareresistanttobitterrot.

SanitationandculturalpracticesBitterrotcontrolisdependentongoodorchardandtreesanitation.Deadwood,includingshootsinfectedwithfireblight,isanimportantsourceofinoculumandshouldberemovedfromtheorchardandburned.

Asspotsenlarge,therotprogressesinwardtowardsthecore.Aftermakingacross-sectionoftheinfectedfruitaV-shaped,brownwaterylesioncanbeobserved(Figure3).Thisisakeydiagnosticfeatureofbitterrot,whichdistinguishesitfromothersummerfruitrots(i.e.whiterotandblackrot).

LeaflesionsandcankersareuncommoninOhio.Leaflesionsbeginassmall,redflecks,whichenlargetoirregularbrownspotsthatare1/16to1/2inchindiameter.Severelyaffectedleavesmaydropoffthetree.Cankersareoval,sunken,andoftenmarkedwithzones(zonate).

Figure3.Crosssectionofbitterrotinfectedfruit.Notethe“V”shapedlesion.Thischaracteristicdistinguishesbitterrotfromwhiterotandblackrot.

ChemicalcontrolFungicidesappliedfromfirstcoveruntilharvestona10-14dayscheduleareeffectiveatcontrollingfruitrotifagoodsanitationprogramisimplemented.Fungicidesarenoteffectiveforcontrollingthecankerphaseofthediseaseonweakenedtrees.Forthemostcurrentfungiciderecommendations,commercialgrowersarereferredtotheMidwestFruitPestManagementGuide (previouslyBulletin780).BackyardgrowersarereferredtoBulletin780, ControllingDiseasesandInsectsinHomeFruitPlantings,whichisavailablefromyourcountyExtensionofficeortheCFAESPublicationsonlinebookstoreatestore.osu-extension.org.

Choppingdeadwoodonthegroundwithaflail-typemowerwillremovemostofthebarkandincreasetherateofdecomposition.Removingandburningmummifiedfruitfromtreesthroughoutthegrowingseasonwillreduceinoculumlevelsduringthecurrentandfollowingseason.

Anypracticethathelpstomaintaintreesinahealthyvigorousconditioniscriticalforcontrollingthecankerphaseofbitterrotdisease.Cankersgenerallydeveloponlyonstressedorweakenedtrees,especiallywinter-injuredtrees.Prunetreesannuallyandmaintainabalancedfertilityprogrambasedonsoilandfoliarnutrientanalyses.






Fire Blight of Apples and PearsMelanie L. Lewis Ivey, Michael A. Ellis


FIRE BLIGHT OF APPLES AND PEARS PLPATH-FRU-22


College of Food, Agricultural, and Environmental Sciences, Department of Plant Pathology

Fire Blight of Apples and PearsMelanie L. Lewis Ivey, Assistant Professor, Department of Plant Pathology, The Ohio State University-Ohio Agricultural Research and Development Center, Wooster, OH.Michael A. Ellis, Professor Emeritus, Department of Plant Pathology, The Ohio State University-Ohio Agricultural Research and Development Center, Wooster, OH.

Figure1.Fireblightdamageonanappletree.DiseaseDevelopmentFireblightfirstappearsinthespringwhentemperaturesgetabove65degreesF.Rain,heavydews,andhighhumidityfavorinfection.Preciseenvironmentalconditionsareneededforinfectiontooccurandasaresultdiseaseincidencevariesconsiderablyfromyeartoyear.

Fireblightbacteriaoverwinterascankersinlivingtissueonthetrunkandmainbranchesandonmummifiedfruit.Primaryinfections(Figure2)areinitiatedduringbloomwhenbacteriaarecarriedfromthecankerstoopenflowersbysplashingrain,pollinatinginsects(i.e.bees,pollenwasps,flies,ants)orduringproductionpracticessuchaspruning.Relativelyfewoverwinteringcankersbecomeactiveandproducebacteriainthespring,butasingleactivecankermayproducemillionsofbacteria,enoughto

Fireblightisacommonandverydestructivebacterialdiseaseofapplesandpears(Figure1).ThediseaseiscausedbythebacteriumErwiniaamylovora,whichcaninfectandcauseseveredamagetomanyplantsintherose(Rosaceae)family(Table1).Onapplesandpears,thediseasecankillblossoms,fruit,shoots,twigs,branchesandentiretrees.Whileyoungtreescanbekilledinasingleseason,oldertreescansurviveseveralyears,evenwithcontinuousdieback.

infectanentireorchard.Thesebacteriamultiplyrapidlyintheblossomnectar,andspreadtothespurs(blossombearingtwigs),newshootsandbranches,resultinginsecondaryinfections.Shootinfectionscanalsooccurthroughwoundscreatedbysuckinginsects(aphids,leafhoppersortarnishedplantbugs),freezeorfrostdamage,windwhipping,winddrivenrain,orhail.Onceashootisinfectedthefireblightbacteriamultiplyrapidlyanddropletsofoozecanbeseenwithin3days.Shootsremainhighlysusceptibletoinfectionuntilvegetativegrowthceasesandtheterminalbudisformed.

Table1.ListofcommonlygrownplantsinOhiothataresusceptibletofireblight.

AppleBlackberryCotoneasterCrabappleHawthorn

MountainAshPyracanthaQuinceRaspberrySpirea


Fire Blight of Apples and Pears—page 2

SymptomsFireblightsymptomsvarydependingonthetissueaffectedandcanalsovarybetweenpearandapple.


BlossomandSpurBlightBlossomandspursymptomsappearinthespring.Bacteriagainentryintothetreeviablossomsandnewshoots.Diseasedblossomsbecomewater-soaked,wiltandturnbrown.Bacteriaspreadrapidlyintootherflowersintheclusterandthenmovedownintothespur.Spursbecomeblighted,turningbrownonapplesandblackonpear(Figure3).

Figure2.Fireblightdiseasecycle.

Fruitblight

Blossominfection Blossom-to-blossom

transferbypollinators

Shootinfection

BlossomandspurblightShootand

twigblight

Infectionsextendintowoodandnewcankersareformed

Overwinteringcanker

Activecankerwithbacterialooze

Bacteriadisseminatedbyinsects,rainandpruning

ShootBlightShootblightstartsatthegrowingtipsofshootsandmovesrapidlydownintoolderportionsofthetwig.Blightedtwigsfirstappearwater-soaked,thenturndarkbrownorblack.Asblightedshootswiltthetwigsbendatthegrowingpointandresembleashepherd’scrookoranupsidedown“J”(Figure4). Blightedleavesremainattachedtothedeadbranchesthroughoutthesummer.Duringwarmandhumidweatherinfectedshootswilloozedropletsofcreamywhitebacteria.

StemCankersAsfireblightbacteriamovethroughblightedtwigsintothemainbranches,thebarksometimescracksalongthemarginoftheinfectedareacausingadistinctcanker(Figure5).Barkonyoungertreesbecomeswatersoakedandthecankershaveadarkbrowntopurplecolor.Sapwoodbeneathacankerhasareddishbrownappearance(Figure5)andmaybesofttothetouch.Cankerscangirdlethemainbranchesandtrunkcausingadditionaldieback.

RootstockSymptomsFireblightsymptomsonrootstocksusuallydevelopnearthegraftunion.Symptomsaresimilartothoseofstemcankers.Fireblightinfectionsinrootstockscanrapidlykillthetreebygirdlingtherootstock.

Figure3.Fireblightonappleblossomsandspurs.

FruitBlightBothappleandpearfruitmaybeblighted.Rottedareasturnbrowntoblackandbecomecoveredwithdropletsofwhitishtancoloredbacterialooze.Fruitremainfirmandeventuallydryoutandshrivelintomummies.



ManagementFireblightisoneofthemostdifficultdiseasesofappleandpeartomanage,andnooneprocedurewillgivecompletecontrol.Thoughmanagementisnotaneasytask,theuseofseveralpracticesinanintegratedmannershouldresultinminimaldamageandlossesfromfireblight.Commercialgrowersshouldconsiderfollowing

arecommendedchemicalsprayprogramforfireblight

Chemicalspraysforfireblightcontrolaregenerallynotrecommendedforbackyardgrowers.Instead,backyardgrowersareencouragedtoplantlesssusceptiblevarietiesanduseothernonchemicalcontrolmeasures,someofwhicharedescribedbelow.Forthemostcurrentsprayrecommendations,

commercialgrowersarereferredtoBulletin506,MidwestFruitPestManagementGuide,andbackyardgrowersarereferredtoBulletin780,ControllingDiseasesandInsectsinHomeFruitPlantings.ThesepublicationscanbeobtainedfromyourcountyExtensionofficeortheCFAESPublicationsonlinebookstoreatestore.osu-extension.org.

ManagementTacticsforFireBlightSelectandplantresistantvarieties. Plantinghighlysusceptiblevarietiesmakesfireblightmanagementextremelydifficult.Whenestablishinganorchardselectandplantappleandpearrootstocks(Table2)andvarieties(Table3)thatarelesssusceptibletofireblight.

Pruneoutfireblightcankersandblightedtwigs.Dormantseason(winter)pruningofblightedtwigsandcankersremovesfireblightbacteriafromtheorchardsothatthebacteriawillnotbetheretostartnewinfectionsinthespring.Eveninorchardswithoutaknownhistoryoffireblight,itisimportanttolookforblightedtwigsandcankersandremovethem.Toremoveblightedtwigs,makeacleancutintohealthytissuethatisatleast4inchesbelowvisiblydeadwood.Cankerscanbecutoutoftrunksorlargebranchesbyremovingdeadtissueuntilhealthytissueisobserved.


Minimizesummerpruningofblightedshoots.Summerpruningofblightedshootscanslowthemovementofbacteriaintheorchardifdonecarefullyandcorrectly.However,ifpropersanitationpracticesarenotused,bacteriacanbeinadvertentlyspreadtohealthytissueandexacerbatethedisease.Pruningofblightedshootsshouldonlybedoneindryweather,cutsshouldonlybemadeintohealthytissuethatisatleast12to15inchesbelowdiseasedwood,andpruningtoolsmustbesanitizedaftereachcut.Toolscanbesanitizedbydippingthemintoa10percentbleachsolution(1volumeofbleachto9volumesofwater)containingafewdropsofliquidsoap.Anewbleachsolutionshouldbepreparedwhenthesolutionappearsdirty.Infectedplanttissueshouldbetakenoutoftheorchardandburnedorplacedintothetrash.

Figure4.Fireblightonanappletwig.Notethecurved“Shepherd’sCrook”atthetipofthediseasedtwigs.ImagecourtesyofMarcusMcCartney,OSUExtensionWashingtonCounty

Infectedplanttissueshouldbetakenoutoftheorchardandburnedorplacedintothetrash.



Followproperpruningandfertilizationpractices.Excessivenitrogenfertilizerandheavypruningwillpromotevigorousgrowthofsucculenttissue,whichisverysusceptibletofireblight.Makefertilizerapplicationsinearlyspringorlatefallaftergrowthhasceased.Neverconductroutinepruning(i.e.pruningtostimulategrowthorshapethetree)atthesametimeaspruningtoremoveblighted,twigs,shootsorcankers.

streptomycinisappliedwhiletheflowersareopen.Forthisreason,streptomycinmayneedtobeappliedmultipletimesuntilpetalfall.Streptomycincanalsobeappliedasarescuetreatmentfollowingasevereweathereventsuchashail,winddrivenrainorhighwinds.

Streptomycinisavailabletobackyardgardenersbutisnotrecommendedduetotheriskofthebacteriabecomingresistanttotheantibioticifitisnotusedproperly.Toreducetheriskofantibioticresistance:


Useful References

Figure5.Fireblightcankersonyoungappletreetrunks(top)andmaturetreebranch(left).Notethereddishbrownappearanceofthesapwoodbeneaththecankeronthematuretreebranch.

Table2.LeveloffireblightresistanceinappleandpearrootstocksS=susceptible; MR=moderatelyresistantand;R=resistantAppleRootstocks ResistanceLevelBud.9* SBud.118 MRGeneva11 RGeneva16 RM.7 RM.9* SM.26 SMM.106 MRMM.111 MRPearRootstocksBartlettseedling SOldHome(OH) ROldHomexFarmingdale(exceptOHxF51)

R

Quinceseedling S*AlthoughBud.9andM.9aresusceptibletofireblight,observationsinOhioindicatethatBud.9islesssusceptibletorootstockinfectionbyfireblightbacteriathanM.9.

• Usetherecommendedrateonthestreptomycinlabel

• Makenomorethanthreetofourapplicationsperseason

• Donotusestreptomycinaftersymptomshavedeveloped

• Donotusestreptomycinforshootblightorcankercontrol

Makeanearlyseasonapplicationofcopper. Treeswithahistoryoffireblightshouldbesprayedwithacopperbasedpesticidetoreducethebuild-upofbacteriaonbudsandbark.Coppershouldbeappliedatsilvertip(whenbudsarejustbeginningtoswell)togreentipandnolaterthanhalf-inchgreen(Figure6).

Spraystreptomycinatbloom.Streptomycinisanantibioticthatcankillfireblightbacteriabeforetheyentertheappletree.Thenectaries oftheflowersarewherebacteriaenterappletrees,soitiscriticalthat







Controlsuckinginsects. Suckinginsectscreatewoundsthroughwhichfireblightbacteriacanenter.Thesepestsshouldbecontrolledthroughoutthegrowingseason.Toprotectbees,donotapplyinsecticidesduringbloom.

Table3.Relativesusceptibilityofcommonappleandpearcultivarstofireblight

HighlySusceptible

ModeratelySusceptible

ModeratelyResistant

AppleBeacon Dutchess JonafreeCortland Empire Melrose

Fuji GoldenDelicious NorthwesternGreening

Gala Haralson NovaEasygroGrannySmith Jonagold PrimaIdared Jonamac PriscillaJonathan Jerseymac QuinteLodi Liberty RedDeliciousMonroe McIntosh RedFreeMutsu(Crispin) Minjon SirPrize

Paulared NorthernSpy PristineRomeBeauty Novamac LibertyWayne Spartan GoldrushWealthy Honeycrisp EnterprizeYellowTransparent Braeburn Sundance

Gingergold Winsap/Staymenstrains

WilliamsPride

Pear

Aurora Maxine Kieffer

Bartlett Seckel Magness

Bosc BeurreD’Anjou MoonglowClapp’sFavorite

HarrowDelight

RedBartlett Honeysweet

ReimerRed Blake’sPride

Starkrimson

ApplytheplantgrowthregulatorApogee. Apogee(prohexadione-calcium)isagrowthinhibitorthatcanreduceshootblightwhenappliedpreventativelyat1to3inchesofnewshootgrowth.Apogeewillnotcontrolblossomorspurblight.OrchardswithahistoryoffireblightorplantedwithfireblightsusceptiblevarietiesorrootstockswillbenefitthemostfromanApogeetreatment.CommercialgrowersshouldcontacttheircountyExtensionEducatororfruittreespecialistforguidanceondeterminingifApogeeshouldbeappliedintheirorchard.Apogeeisnotrecommendedforbackyardgrowers.

Figure6.Applebudsatthesilvertip(left)andearlygreentipstage(right).ImagescourtesyofMarkLongstroth,MichiganStateUniversityExtensionandDaveSchmitt,RutgersCooperativeExtension.

ThebiologicalcontrolproductSerenadeGardenDefense,whichcontainsbeneficialantibioticproducingbacteria(Bacillussubtilis),canbeusedbybackyardgardenersinplaceofstreptomycin.Likestreptomycin,SerenadeGardenDefenseshouldbeappliedtoopenflowersthroughbloom.


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OHIO STATE UNIVERSITY EXTENSION

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Reducing 2,4-D and Dicamba Drift Risk to Fruits, Vegetables and Landscape PlantsDouglas J. Doohan and Roger A. Downer, Horticulture and Crop Science

2,4-D and dicamba are common examples of a class of herbicides known as synthetic auxins. Auxins are naturally occurring plant hormones. Synthetic auxins can be used to kill weeds by inducing hormonal effects on sprayed plants. These effects are usually characterized by severe distortion of stems and leaves. Unintentional application of a synthetic auxin herbicide to a sensitive plant, either through direct application or spray drift, often causes severe injury, loss of yield, and even death of the non-target plants. Not all fruits, vegetables and landscape plants are highly sensitive to synthetic auxins, but most will react to exposure in characteristic ways (Figures 1–3).

Why should you be concerned about synthetic auxin herbicides? Simply because 2,4-D and dicamba are likely to be used much more extensively and intensively throughout the Midwest, starting in the near future. A little history will help to put the elevated risk in perspective. 2,4-D is considered to be the first modern herbicide and has been in con-tinuous use on farms, roadsides and lawns since the late 1940s. Dicamba was first released as a commercial product in the 1960s and continues to be used for weed control in corn, wheat, pastures and lawns. Unfortunately, some older 2,4-D and dicamba formulations were notoriously prone to spray drift and to post-application volatilization. This caused unintentional damage to, and even death of, sensitive crops and other plants present in nearby fields and homesteads. Over time, lawsuits and government regulations resulted in changes to the way these herbicides were used, and to physical/chemical characteristics of the formulations, to reduce the potential for off-site movement. Nevertheless, 2,4-D and dicamba have been among the most likely herbicides to be implicated in spray drift cases. For example, survey results of state pesticide control officials listed 2,4-D as the herbicide most often involved in pesticide drift incidents (crop damage) every year the survey has been taken (2005 AAPCO Pesticide Drift Enforcement Survey). The same survey lists dicamba as the 3rd most commonly involved in drift incidents for two years in a row.

This level of drift occurrence far outpaces the relative use of these herbicides: 2,4-D is the 7th most commonly applied conventional pes-ticide active ingredient and dicamba is not even among the top 25. This is because these active ingredients are toxic to many broadleaf plants at ultra-low concentrations; hence, drift damage symptoms develop readily and are easy to see and identify.

There are several reasons why these herbicides are being used more by grain farmers. The main reason is that proliferation of weed species with high levels of resistance to the most commonly used herbicide, glypho-sate, is making weed control with current methods ineffective (Figure 4).

In response, new approaches to managing resistant biotypes are being pursued. These new approaches currently center on the Figure 1.- 2,4-D damage on grapes.

Reducing 2,4-D and Dicamba Drift Risk to Fruits, Vegetables, and Landscape Plants

Douglas Doohan and Roger DownerDepartment of Horticulture and Crop Science The Ohio State University

AGRICULTURE AND NATURAL RESOURCES FACT SHEET

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OHIO STATE UNIVERSITY EXTENSION

HYG-6105-15

Reducing 2,4-D and Dicamba Drift Risk to Fruits, Vegetables and Landscape PlantsDouglas J. Doohan and Roger A. Downer, Horticulture and Crop Science

2,4-D and dicamba are common examples of a class of herbicides known as synthetic auxins. Auxins are naturally occurring plant hormones. Synthetic auxins can be used to kill weeds by inducing hormonal effects on sprayed plants. These effects are usually characterized by severe distortion of stems and leaves. Unintentional application of a synthetic auxin herbicide to a sensitive plant, either through direct application or spray drift, often causes severe injury, loss of yield, and even death of the non-target plants. Not all fruits, vegetables and landscape plants are highly sensitive to synthetic auxins, but most will react to exposure in characteristic ways (Figures 1–3).

Why should you be concerned about synthetic auxin herbicides? Simply because 2,4-D and dicamba are likely to be used much more extensively and intensively throughout the Midwest, starting in the near future. A little history will help to put the elevated risk in perspective. 2,4-D is considered to be the first modern herbicide and has been in con-tinuous use on farms, roadsides and lawns since the late 1940s. Dicamba was first released as a commercial product in the 1960s and continues to be used for weed control in corn, wheat, pastures and lawns. Unfortunately, some older 2,4-D and dicamba formulations were notoriously prone to spray drift and to post-application volatilization. This caused unintentional damage to, and even death of, sensitive crops and other plants present in nearby fields and homesteads. Over time, lawsuits and government regulations resulted in changes to the way these herbicides were used, and to physical/chemical characteristics of the formulations, to reduce the potential for off-site movement. Nevertheless, 2,4-D and dicamba have been among the most likely herbicides to be implicated in spray drift cases. For example, survey results of state pesticide control officials listed 2,4-D as the herbicide most often involved in pesticide drift incidents (crop damage) every year the survey has been taken (2005 AAPCO Pesticide Drift Enforcement Survey). The same survey lists dicamba as the 3rd most commonly involved in drift incidents for two years in a row.

This level of drift occurrence far outpaces the relative use of these herbicides: 2,4-D is the 7th most commonly applied conventional pes-ticide active ingredient and dicamba is not even among the top 25. This is because these active ingredients are toxic to many broadleaf plants at ultra-low concentrations; hence, drift damage symptoms develop readily and are easy to see and identify.

There are several reasons why these herbicides are being used more by grain farmers. The main reason is that proliferation of weed species with high levels of resistance to the most commonly used herbicide, glypho-sate, is making weed control with current methods ineffective (Figure 4).

In response, new approaches to managing resistant biotypes are being pursued. These new approaches currently center on the Figure 1.- 2,4-D damage on grapes.


Reducing 2,4-D and Dicamba Drift Risk to Fruits, Vegetables and Landscape Plants—page 2

2,4-D-based Dow AgroSciences’ EnlistTM Weed Control System and Monsanto’s dicamba-based Roundup Ready® Xtend Crop System. The EnlistTM system involves genetic modifications to corn and soybeans to produce tolerance to 2,4-D and glyphosate. The Xtend system will provide tolerance to dicamba and glyphosate in soybean.

How quickly can you expect increased use of 2,4-D or dicamba in fields near you? It’s difficult to say with certainty but on September 17, 2014, the U.S. Department of Agriculture issued its decision deregulating Dow AgroSciences’ EnlistTM corn and soybean traits in the United States. Following this action Dow AgroSciences’ 2,4-D containing Enlist DuoTM herbicide, the companion herbicide to the EnlistTM traits, was approved by the U.S. Environmental Protection Agency (EPA) on October 15, 2014. The Xtend system is awaiting regulatory approval.

So why should we be concerned?Ohio grain farmers grow more than 4 million acres of soybean and more than 3 million acres of corn, nearly all of which

are sprayed with herbicides to control weeds. A consequence of the new genetically modified (GM) crops is that many, perhaps nearly all, of these acres will be sprayed with 2,4-D or dicamba in the future. Not only is use of these herbicides likely to increase, but patterns of use will change as well. A stated benefit of the EnlistTM and the XtendTM weed control systems is they give extended application flexibility before planting, at planting, and after planting. This intended change in the use pattern increases the likelihood that applications to corn and soybeans will coincide with the more susceptible growth stages of sensitive crops and plants such as fruits, vegetables and landscape plants. Changing weather patterns may further impact application timing result-ing in applications coinciding with susceptible growth stages of sen-sitive plants. In 2013 an unprec-edented number of drift damage incidents involving vineyards occurred in Ohio due in part to weather conditions that resulted in burndown herbicide applica-tions coinciding with susceptible growth stages of grapes. Though

Figure 2. Grape response to simulated drift of dicamba. Figure 3. 2,4-D damage on tomato.

Figure 4. Glyphosate resistant horseweed in soybeans. (photo courtesy of Mark Loux.)



vineyard acreage is small compared to row-crop acreage, the fact that vines are a perennial crop, and grape harvests and products have high value, means that a little damage can have large economic consequences.

How is the risk being reduced?Many specialty crop growers fear

that these new GM crop technolo-gies and their specialty crops cannot co-exist. However, the perceived risks may not be as high as many people fear. 2,4-D and dicamba have, after all, been used on millions of acres since the 1960s and while drift and volatility have been an issue (Figure 5), the approved use of these products has not resulted in widespread catastrophic dam-age. Dow AgroSciences, Monsanto and BASF have taken great care to minimize the known negative attri-butes of older 2,4-D and dicamba formulations. Dow AgroSciences has developed Enlist DuoTM that includes a new low-volatility for-mulation of 2,4-D with minimized drift potential, lower odor, and bet-ter handling characteristics than currently available 2,4-D amine or ester formulations. BASF plans to produce a “technologically advanced” dicamba formulation branded EngeniaTM for use on dicamba-tolerant crops, including soybeans and cotton, that has been formu-lated to provide increased weed control and reduced volatility. Educational and outreach programs to farmers, dealers and commercial applicators (EnlistTM Ahead) to promote and encourage good stewardship of the new system have also been initiated. Risks associated with dicamba will also be reduced through product formulation and stewardship programs. A premix of dicamba and glyphosate herbicide branded as Roundup XtendTM with VaporGripTM technology will be introduced upon regulatory approval of the Roundup Ready® Xtend Crop System. This low-volatility formulation will be labeled for use before, at and after planting.

What spray drift and volatilization are and how to prevent them from happening

Spray drift—The Environmental Protection Agency (EPA) defines spray drift as the movement of pesticide dust or droplets through the air at the time of application or soon thereafter, to any site other than the area intended.

As a result of extensive research, the causes and fixes of spray drift are well known and documented. For example, using nozzles and pressures that result in the creation of fine spray droplets, and/or spraying during windy conditions greatly increase the risk of drift. Pesticide labels routinely contain much information on steps that applicators should take to reduce the risk of drift occurring. The instructions on the pesticide label are given to ensure the safe and effec-tive use of pesticides with minimal risk to the environment. Many drift complaints result from application procedures that violate the label instructions.

Volatilization—Volatilization occurs when pesticide surface residues change from a solid or liquid to a gas or vapor after an application of a pesticide has occurred. Once airborne, volatile pesticides can move long distances off site.

The potential for a pesticide to volatilize is related to the vapor pressure of the chemicals involved. Pesticides with high vapor pressure are likely to be more volatile than those with low vapor pressure. Pesticides known to have the potential to vaporize carry label statements that warn users of this fact. While there are things that the applicator can control (e.g., nozzle tip, pressure, boom height) to reduce spray droplet or dust drift, vapor drift is dependent upon the weather conditions at the time of application since the likelihood of pesticide volatilization increases as temperature and wind speed increases and if relative humidity is low.

Figure 5. Schematic showing herbicide vapor drifting into sensitive non-target crop.



Despite an applicator’s best intentions, the risk of spray drift occurring is always present, most often as the result of the factors involved that are not under the applicator’s control, e.g., changing weather conditions. To reduce mis-understanding, we suggest an ongoing dialogue between specialty crop growers and their neighbors who grow corn and soybean and with commercial spray applicators who are likely to use 2,4-D and dicamba. Help these individuals better understand specialty (fruit, vegetable and nursery crops) production and the impact of it on the state’s economy. Promote awareness among agronomic crop producers that vineyards, extensive landscape plantings, or other suscep-tible crops are located in their neighborhood. Given the recent rapid growth in the number of vineyards, it is likely that some neighboring farms don’t even know grape growers exist in their vicinity, let alone the cost involved in establish-ing just one acre of wine grapes or the potential value of the crop. Creating and maintaining a heightened awareness of the industry is probably the most important way to reduce risk of future herbicide damage and the lawsuits that will inevitably follow.

The following steps may be useful to help the specialty crop industry develop a process for creating and maintaining awareness and reducing the risk of drift damage.

Step 1. Inform your neighbors.Develop and maintain a good relationship with your neighbors. A good relationship starts with open communication.

Offer a tour of your operation, explain how damaging drift of glyphosate, 2,4-D and dicamba can be to your crops. In the case of vineyards, make sure to point out the potential for herbicide drift to cause yield loss, poor grape quality, increased susceptibility to cold injury, and reduction in long-term profitability. Discuss the possibility of planting buffer vegetation between your crops and your neighbors’ crop(s) to reduce risk.

Step 2. Mark your farm or vineyard on an online database.Neighboring farmers and commercial spray applicators will need accurate information on where specialty crops are

being grown. The Ohio Department of Agriculture has launched a website designed to incorporate coordinates for fields planted to sensitive crops into Google Maps. This site is known as the Ohio Sensitive Crop Registry (Figure 6) (agri.ohio.gov/scr).

Applicators can check this website for proximity of sensitive crops to fields they are planning to spray. If you farm near roadways or other rights-of-way contact your county or state highway department, power company, etc., since hormone-type herbicides are likely used for weed control in those situations already.

Figure 6. Screenshot of the home page of the Ohio Sensitive Crop Registry website.



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Step 3. Manage drift of the herbicides used on your own farm or vineyard.Set an example of pesticide stewardship. Fruits and vegetables include the most intensively sprayed crops grown

in the United States. Consider the unspoken message you send to the community every time you apply pesticides, especially when using high pressure/high volume equipment. While many herbicides are registered for fruits and veg-etables, most have severe restrictions due to the inherent high sensitivity of most crops. In some cases the herbicide injury problem is caused by an application made by the owner, rather than by a neighbor. The likelihood of drift is a multiple of many factors, but some important ones are wind speed, droplet size (determined primarily by nozzle type), the height of the nozzle above the ground or canopy, and the operating pressure. Drift can be minimized by spraying on a morning or evening with low but not zero wind conditions (3–10 mph), keeping the spray boom and nozzles close to the ground, reducing pressure (less than 30 psi), and using low drift nozzles that generate large droplets.

What if drift damage occurs or is suspected?Know the symptoms of 2,4-D and dicamba injury on your crops and plan on scouting regularly during the time when

grain growers are spraying (Figures 1 and 2). Early symptom detection (within a few days of drift) is important if you hope to detect residues of the causal agent—a data point that may be of great value in obtaining compensation.

Prevention is better than cure. We encourage open and frank communication between all parties. Spell out the risk. Inform your neighbors about the high dollar value per acre of the crops you grow. Many specialty crops, and especially grapes, are relatively small in acreage but high in value, and are highly sensitive to trace amounts of 2,4-D and dicamba. Many are perennials and the consequences of drift damage can be dire and long-lasting.

Filing a drift complaintEven with the best of intentions drift incidents can happen. Before filing a drift complaint, talk to other people such

as an Extension Educator to gather additional information. It is also a good idea to inform the suspected pesticide applicator about your concerns and try to work out a satisfactory solution. Being proactive when problems are first observed is critical. Document when symptoms were first noted and any knowledge you may have of pesticide spraying on adjacent properties. Take lots of pictures of damaged and injury-free plants, including close-ups. While laboratory analysis is not always called for, taking samples of damaged tissues is a good idea. Take samples from several plants, seal them in a zip-close plastic bag, and place them immediately in a freezer. It is also a good idea to take a second sample of tissues from plants of the same cultivar that are not showing injury symptoms.

If you are convinced that your crops or landscape plants were damaged by herbicide drift, you can file a complaint with the office of Pesticide and Fertilizer Regulation at the Ohio Department of Agriculture. Call 1-800-282-1955, then select option 31 and tell the operator that you want to file a pesticide use complaint. It is also very helpful if you can provide the name and address of the pesticide applicator. This could initiate an investigation.

For more information contact:Dr. Doug DoohanProfessor of Horticulture and Crop ScienceOARDC1680 Madison AvenueWooster, OH 44691Email: [email protected]

79Pesticide Safety Education Program, Ohio State University ExtensionCopyright © 2009, The Ohio State University

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Managing Downy Mildew in Organic and Conventional Vine Crops

Downy mildew can be a serious disease on any vine crop, but may be especially devastating to

cucumbers where the appearance of initial symptoms and complete defoliation may be separated by only a few days.

SymptomsDowny mildew causes a variety of symptoms de-

pending on cucurbit type. On cucumber, water-soaked lesions on the underside of the leaf are often observed first. Yellow, irregularly shaped lesions confined by the small leaf veins appear soon after on the top of

the leaf. These lesions then turn brown and may drop out of the leaf. The “checkerboard” arrangement of lesions is characteristic of cucumber downy mildew. Symptoms normally appear 4–12 days after infection. On cantaloupe, the somewhat angular lesions tend to have a yellow halo around them. On watermelon, the spots may or may not be angular, normally turning brown or black with the leaf developing an upward curl. On pumpkins and winter squash, the symptoms may resemble powdery mildew, causing a yellow spot-ting that tends to brown out. As the lesions age, they usually become necrotic on all types of cucurbits and

Ron Becker OSU Extension, Wayne County

Sally A. MillerDepartment of Plant Pathology

Figure 1. Initial downy mildew symptoms on cucumber Figure 2. Advanced downy mildew symptoms on cucumber

Managing Downy Mildew in Organic and Conventional Vine CropsSally Miller



Managing Downy Mildew in Organic and Conventional Vine Crops—page 2


the leaves often senesce. This dieback is normally first noticed on the oldest leaves near the center of the plant.

Regardless of the variability in appearance of the leaf lesions among the different cucurbits, the one similarity and diagnostic sign is the presence of purplish-gray sporangia on the bottom side of the leaf within the lesions. These are most readily observed when conditions are cool and moist, with or without the aid of a hand lens. They may also appear when an infected leaf is placed in a closed plastic bag with a damp paper towel for 12–24 hours. The leaves are the only portion of the plant directly affected by downy mildew, though the resulting loss in leaf surface can cause loss of yield, misshapen fruit, and sunscald.

Causal OrganismDowny mildew is caused by Pseudoperonospora

cubensis, an oomycete pathogen more closely re-lated to water molds such as Phytophthora than to true fungi. There are multiple pathotypes of P. cubensis; watermelons, pumpkins, and squash are incompatible with several pathotypes, while cucumbers and cantaloupe are susceptible to them all. There are also several strains within each patho-type, to which various cultivars of each type of cucurbit show varying degrees of susceptibility. P. cubensis can survive and sporulate only on green (living) tissue of the host, and therefore cannot natu-rally overwinter north of Mexico or the southernmost extremes of the United States.

Figure 3. Downy mildew symptoms on cantaloupe Figure 4. Downy mildew symptoms on watermelon

Figure 5. Downy mildew symptoms on pumpkin Figure 6. Close-up of downy mildew on pumpkin



Sporangia are the reproductive structures and also spread the disease on wind currents. Sporangia are produced on the undersides of the leaves when conditions are humid and nighttime temperatures are between 55 and 75 degrees F. The transport and survival of these sporangia are highly dependent on weather conditions. Cloudiness is especially impor-tant as direct sunlight or excessive UV light can cause the sporangia to desiccate. Rainfall can also wash the sporangia out of the air if it occurs before the spo-rangia travel much of a distance from source area, or it may help to deposit them in production fields. Upon deposition of the sporangia on a leaf surface, the absence of free moisture on the leaf may prevent infection, though only 2–6 hours of free moisture are required. Likewise, temperatures outside of the acceptable range for infection (41–82 degrees F) may also inhibit infection.

For many years, downy mildew was not reported in Ohio cucurbit fields until late August or Septem-ber, being dependent on remnants of hurricanes to carry the spores northward. Presence of the disease was often considered inconsequential as many crops were considered mature, and the loss of leaf surface at that point did little to reduce the yield of crops such as pumpkins. For late cucumber or melon plantings, fungicides could be applied for control measures. More recently, cucurbit downy mildew has been reported as early as late June, possibly due to over-wintering of the disease in greenhouses in northern

North America or use of transplants produced in the southern United States or northern greenhouses. New strains of downy mildew have also developed that are resistant to commonly used fungicides, and have overcome the genetic resistance of some cul-tivars. These midseason infections have resulted in heavy yield losses where preventive measures have not been taken.

ManagementCultural Practices

The same cultural control measures are suggested as part of an IPM effort whether a crop is conventional or organic, in that they may help to reduce or delay the chances of an initial infection.1. Despite some strains of downy mildew overcom-

ing currently available genetic resistance, the use of disease-resistant or tolerant cultivars is still highly recommended as some degree of resistance remains. A list of these can be found at the North Carolina State University Cucurbit Breeding web site at http://cuke.hort.ncsu.edu/cucurbit/cuke/cukemain.html.

2. Select growing sites with good air drainage, full sunlight, and low humidity.

3. Avoid overhead irrigation to prevent leaf wet-ness.

4. Insure adequate, but not excessive fertility.5. Monitor the crop frequently, and make use of the

North American Plant Disease Forecast Center at http://www.ces.ncsu.edu/depts/pp/cucurbit to monitor reports of downy mildew throughout the country. Local updates are also available on VegNet (http://www.ag.ohio-state.edu/~vegnet/).

6. If early in a downy mildew epidemic, removal of infected plants may help to slow the spread of the disease. When doing this, make sure not to spread the disease by hand or infested equipment.

Chemical ControlFor conventional growers, it is suggested that pro-

tectant fungicides be applied on a 7–10 day schedule upon emergence of the seedling or transplanting. When downy mildew is detected in the area, a curative-type fungicide should be added to the spray mixture

Figure 7. Purplish-gray sporangia on the bottom side of a cucumber leaf




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Visit Ohio State University Extension’s web site “Ohioline” at: http://ohioline.osu.edu

and the spray schedule should be shortened to 5–7 days. Consult the Ohio Vegetable Production Guide (OSU Extension Bulletin 672) for recommendations and make sure to rotate fungicides with different modes of action.

For organic growers, there are several alternative fungicides labeled for cucurbit downy mildew, in-cluding copper-based fungicides. Growers should be cautious in applying copper, as it can be phytotoxic to cucurbits, and high levels in soil are toxic to earth-worms and other beneficial organisms. Phytotoxicity is most common during cool, moist conditions, which are also the most favorable for downy mildew. A list of the other alternative fungicides can be found at the National Sustainable Agriculture Information Services “Downy Mildew in Cucurbits” web page at http://attra.ncat.org/attra-pub/downymildew.html#ref4. Make sure to check with OMRI http://www.omri.org and your organic certifier to determine if the suggested products are currently considered acceptable for organic production.

Resources“Downy Mildew in Cucurbits,” National Sustainable

Agriculture Information Service, http://attra.ncat.org/attra-pub/downymildew.html#ref4

North Carolina State University Cucurbit Breeding Program, http://cuke.hort.ncsu.edu/cucurbit/cuke/cukemain.html

“Cucurbit Downy Mildew Forecast Home,” North American Plant Disease Forecast Center, http://www.ces.ncsu.edu/depts/pp/cucurbit

“Update on Managing Downy Mildew in Cucur-bits,” Vegetable MD Online, Cornell University, http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Cuc_Downy.htm

“Cucurbit Downy Mildew Caused by Pseu-doperonospora cubensis,” Extension Collab-orative Wiki, http://collaborate.extension.org/wiki/Cucurbit_Downy_Mildew_Caused_by_ Pseudoperonospora_cubensis

AcknowledgmentsAll photos by Sally A. Miller.


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