insect and disease problems of tomatovirtual.chapingo.mx/dona/paginacbasicos/enfermtomato.pdf ·...

Insect and Disease Problems of TomatoTo use the Master Gardener Online Disorder Identification Guide, first select the plantproblem groupings below. Then match the symptoms of the sample or the verbal descriptionof the sample to the image or images in the composites presented that most closely resemblethe problem.

Click once on an image to see a larger view of that problem and a description of thesymptoms. If you are unsure of the diagnosis, go back to the composite and view otherrelated images.

If the image and description match the problem you aretrying to diagnose, click on the button to go to the TexasPlant Disease Handbook to view recommended controls.

Disorders of GreenTomato Fruits

MORE Disorders ofGreen Tomato Fruits

Disorders of RipeTomato Fruits

Disorders of TomatoLeaves

MORE Disorders ofTomato Leaves

Disorders of TomatoStems

Disorders AffectingTomato Roots

Master Gardener Online

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/mgprob.html [05/07/2001 02:18:17 p.m.]

Disorders of Green Tomato Fruit. Click on the photo that best matches problem you're trying todiagnose.

Green Tomato Fruit Disorders

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomfruit/grnfruit/tomfruitg1.html [05/07/2001 02:18:30 p.m.]

BacterialSpeckCausal Agent:Pseudomonas syringaepv. tomato

Bacterial speck iswidely distributed.Symptoms may appearon any plant part.Leaves of infectedplants are covered by

small, dark brown, irregular patches of necrotic tissue that are surrounded by yellow halos. Diseaseseverity is increased by leaf wetness, from sprinkler irrigation, rain, or heavy dews.

Control: Minimize wetting of the leaves by using drip or furrow irrigation. Copper sprays provideeffective control.


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomfruit/grnfruit/5.2.html [05/07/2001 02:18:35 p.m.]

Bacterial SpotCausal Agent: Xanthomonas campestris pv. vesicatoria

Dark brown water soaked spots appear on the leaves; laterthese spots become blackish, and eventually the affectedtissue drops out leaving a hole in the leaf. Black, raisedspecks that later become scab-like spots appear at the sametime on fruit.

Control: Crop rotations and careful transplant selection areimportant. Copper sprays provide some control. Goodsanitation practices including prompt plow-down of stubbleand weed control help prevent the disease.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Bacterial Spot

AlternariaCanker(fruit symptoms)

Causal Agent: Alternaria alternata f.sp. lycopersici

Symptoms of Alternaria canker appearon stems, leaves and fruit. Brown orblack necrotic lesions are usually visibleon plants from which infected fruit are

picked. Fruit are infected when green, but symptoms persist into the ripening period. Sunken grayishlesions are present on fruit.

Control: Fungus overwinters in crop residue and is easily spead by wind. Wounding of young plants (bymechanical damage or pruning) provides an entry site for infection. Furrow or drip irrigation is preferredover sprinkler irrigation. Preventative fungicide sprays may be required if a "zero tolerance" for defectsproduction system is needed.



Tobacco MosaicVirus(fruit symptoms)

Causal Agent: Tobacco Mosaic Virus

Tobacco mosaic virus (TMV) infectedplants have a green/yellow mottledappearance and are usually stunted.Infected fruit may have necrotic brownpatches on them.

Control: The virus is most commonly transmitted by handling or mechanical damage. Workers whosmoke may infect plants with virus particles left on their hands after handling cigarettes. A variety ofinsects can also transmit the disease from infected weeds in the Solanaceae. Avoid planting in a fieldwhere infected tomato or tobacco plants were grown, and in greenhouse situations, all pruning equipmentshould be steam sterilized regularly. Use resistant varieties.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Tobacco Mosaic Virus

BacterialCankerCausal Agent: Corynebacteriummichiganense

Bacterial canker is characterized bywilting and eventual death of thelower leaves, with the leaves dryingup while still attached to the stem.Vascular tissue is discolored, brown,or brownish-yellow, and acharacteristic yellow slime can be

squeezed from affected stems. The bacterium that causes this disorder may be seed or soil born.

Control: Crop rotations and careful seed source selection are primary considerations. Seed beds ininfected areas should be sterilized. Mechanical damage to the transplants (such as topping) spreads thedisease.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Bacterial Canker

BuckeyeRotBuckeye rot is one ofa number of fruitrotting diseases thatattacks both green andripe fruit, especiallywhere the fruittouches the soil. The

lesion is rounded with alternating bands of light and dark brown in concentric circles. The lesion appearswater-soaked at first, but later may become leathery on the surface.

Causal Agent: Phytophthora parasitica

Control: Staking or plastic mulch to prevent fruit from contacting the soil is an effective control. Thedisease is worse in hot, wet weather. Fungicides offer little control to soil-contact type diseases.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Buckeye Rot

Late BlightCausal Agent: Phytophthora infestans

Lesions on leaves appear as largewatersoaked areas, that eventually turnbrown and papery. Fruit lesions are largeirregular greenish-brown patches having agreasy rough appearance. Green to blackirregular lesions are also present on thestems.

Control: The fungus develops duringperiods of cool wet weather. Fungicidesprays as a preventative measure during

these periods may be needed if the crop is being grown near large areas of tomato relatives (Solanaceousweeds, potatoes).

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Late Blight

More Disorders of Green Tomato Fruit. Click on the photo that best matches problem you're trying todiagnose.

More Green Tomato Fruit Disorders

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomfruit/grnfruit/tomfruitg2.html [05/07/2001 02:19:18 p.m.]

Blossom End RotBlossom end rot can affect fruit at all stagesof development. The characteristicsymptom is a progressive deterioration ofthe blossom end of the fruit, from awater-soaked appearance to a sunken, black,leathery lesion. While secondary fungalinfections may occur, blossom end rot is aphysiological disorder caused by calciumdeficiency induced by water stress.

Causal Agent: Physiological Disorder

Control: Careful water managementpractices are a key. Irrigation and/or

mulching are important. Application of lime or calcium prior to planting may help. Liquid fertilizationusing calcium nitrate can be used for small plots.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Blossom End Rot

Spotted WiltFruit are malformed, with raised yellow, red,and green mottled bull's eye rings. Plants fromwhich fruit are harvested are stunted, witholder leaves turning yellow. The virus iscarried by flower and onion thrips that havecarried the virus from infected weeds andornamentals.

Causal Agent: Tomato Spotted Wilt Virus

Control: Elimination of plants that serve as hosts to thrips is the most important control measure. Cleancultivation, with special attention to border strips is important. Locate production away from large grainfields.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Spotted Wilt

Sun ScaldFruit have yellowish orwhitish patches on sideexposed to sunlight. Thesepatches turn leathery and dryout. They may becomeinfected with various types ofmold as secondary infectionsin the wounded tissue. Fruitprotected by shade from leafcover or shading material areunaffected.

Causal Factor: Lack of LeafCover

Control: Select varietiesnoted to retain leaf coverthroughout season. Use goodfungicide/insecticide programto prevent leaf loss due toinsects and disease. On smallscale, can cover fruit withstraw or shade plants with rowcover.


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomfruit/grnfruit/43.html [05/07/2001 02:19:29 p.m.]

PinwormDamageBlackened cavities are presentnear the stem scar of greentomato fruit, and someexcrement may be presentaround the cavities. If fruit is cutopen, a tunnel will be presentthroughout the fruit cavity. Thelarvae (the worm) may or maynot ve present.

Causal Agent: Pinworm

Control:


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomfruit/grnfruit/pworm.html [05/07/2001 02:19:33 p.m.]

RadialCrackingFruit develop large cracksradiating out from the stemscar. Cracking may occur ongreen fruit. Cracks appearweathered and corky if theyoccur in green fruit. Fruit maydevelop any of a number offungal fruit rots at the point ofcracking.

Causal Factor: Environmental Stress

Control: Select varieties that have less cracking under your growing conditions. Prevent wide swings inmoisture by even irrigation or mulching.



Tomato Fruit Disorders. Click on the photo that best matches problem you're trying to diagnose.

Tomato Fruit Disorders

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomfruit/tomfruit.html [05/07/2001 02:19:43 p.m.]

AnthracnoseAnthracnose is a common fruit disorder affectingprimarily ripe fruits. Lesions appear first as sunken,circular spots that deepen and become dark in themiddle. The lesion often takes on a "bull's eye"appearance due to the concentric ring effect of theenlarging lesion. Water splashed on the fruit duringrains or irrigation carry the fungal spores to the fruit.

Causal Agent: Colletotrichum coccodes and otherColletotrichum species.

Control: Crop rotations, fungicide sprays.

See


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomfruit/ripefruit/9.1.html [05/07/2001 02:19:46 p.m.]

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Anthracnose

Early BlightFruit damage caused by early blight is theappearance of sunken, leathery, dark lesionsnear the stem scar. Fruit become infectedwhen green. This disorder is morecommonly known as a foliar or stemdisorder. Leaf infection is notable first on

older leaves with the appearance of irregular brown necrotic lesions surrounded by an area of yellowingtissue. Early season damp rainy weather encourages infection, and the symptoms become noticeablerapidly with increasing temperatures in mid-season. Heavy dews and overhead irrigation can contributeto disease spread.

Causal Agent: Alternaria solani

Control: Crop rotations, fungicide sprays.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Early Blight

Blossom End RotBlossom end rot can affect fruit at all stages ofdevelopment. The characteristic symptom is a progressivedeterioration of the blossom end of the fruit, from awater-soaked appearance to a sunken, black, leatherylesion. While secondary fungal infections may occur,blossom end rot is a physiological disorder caused bycalcium deficiency induced by water stress.

Causal Agent: Physiological Disorder

Control: Careful water management practices are a key. Irrigation and/or mulching are important.Application of lime or calcium prior to planting may help. Liquid fertilization using calcium nitrate canbe used for small plots.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Blossom End Rot

Black MoldNumerous fungi cause fruit rots on tomato.Lesions may be superficial, or black or brownsunken areas that extend into the internal fruittissue. Lesions often occur near the stem endscar.

Causal Agent: Any of a number of speciesincluding Pythium, Phytophtora, Rhizoctonia,and Alternaria.

Control: Fruit should be kept off the soil (ifpossible), and surface wetting should beminimized. Furrow or drip irrigation ispreferred over sprinkler irrigation.Preventative fungicide sprays may be required

if a "zero tolerance" for defects production system is needed.



Sour RotNumerous fungi cause fruit rots on tomato.Lesions are water-soaked, and may have awhite scummy growth in the cracks. Lesionsoften occur near the stem end scar.


Control: Fruit should be kept off the soil (ifpossible), and surface wetting should beminimized. Furrow or drip irrigation ispreferred over sprinkler irrigation.Preventative fungicide sprays may be requiredif a "zero tolerance" for defects production

system is needed.



Cloudy SpotFruit are covered with white or yellowflecks and patches that occur in the tissuejust beneath the skin. Peeling fruit in theaffected areas reveals white corky (not red)tissue.

Causal Agent: Stink bug feeding.

Control: Stink bugs often attack tomatoesfrom surrounding weeds. Feeding on youngfruit is barely noticeable, but improperripening and blemishes develop as fruitmatures. Use a recommended insecticidalprogram to control stink bugs.



Cottony LeakNumerous fungi cause fruit rots on tomato.Large areas of the fruit appear water-soaked,with off color darker or lighter patches. Fruitmay appear intact until touched. Handlingusually punctures skin and internal waterytissue escapes.


Control: Fruit should be kept off the soil (ifpossible), and surface wetting should be

minimized. Furrow or drip irrigation is preferred over sprinkler irrigation. Preventative fungicide spraysmay be required if a "zero tolerance" for defects production system is needed.



Alternaria StemCankerSymptoms of Alternaria canker appearon stems, leaves and fruit. Brown orblack necrotic lesions are usually visibleon plants from which infected fruit arepicked. Fruit are infected when green,but symptoms persist into the ripeningperiod. Sunken grayish lesions arepresent on fruit.

Causal Agent: Alternaria alternata.

Control: Fungus overwinters in crop residue and is easily spead by wind. Wounding of young plants (bymechanical damage or pruning) provides an entry site for infection. Fruit should be kept off the soil (ifpossible), and surface wetting should be minimized. Furrow or drip irrigation is preferred over sprinklerirrigation. Preventative fungicide sprays may be required if a "zero tolerance" for defects productionsystem is needed.



Tomato Leaf and Stem Disorders. Click on the photo that best matches problem you're trying todiagnose.

Tomato Leaf Disorders

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/tomleaf.html [05/07/2001 02:20:37 p.m.]

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/leafcomp1.map

BacterialCankerCausal Agent:Corynebacteriummichiganense

Bacterial canker ischaracterized by wiltingand eventual death of thelower leaves, with theleaves drying up while stillattached to the stem.Vascular tissue isdiscolored, brown, orbrownish-yellow, and acharacteristic yellow slimecan be squeezed from

affected stems. The bacterium that causes this disorder may be seed or soil born.

Control: Crop rotations and careful seed source selection are primary considerations. Seed beds ininfected areas should be sterilized. Mechanical damage to the transplants (such as topping) spreads thedisease.

See


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/4.1.html [05/07/2001 02:20:43 p.m.]

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Bacterial Canker

Bacterial SpotCausal Agent: Xanthomonas campestrispv. vesicatoria

Dark brown water soaked spots appearon the leaves; later these spots becomeblackish, and eventually the affectedtissue drops out leaving a hole in theleaf. Black, raised specks that laterbecome scab-like spots appear at thesame time on fruit.

Control: Crop rotations and carefultransplant selection are important.Copper sprays provide some control.Good sanitation practices includingprompt plow-down of stubble and weedcontrol help prevent the disease.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Bacterial Spot

Gray Leaf SpotCausal Agent: Stemphylium floridanum and S. botryosum

Small brownish-black specks first appear on undersides ofleaves. These later develop into larger necrotic areas, and thetissue often falls out, leaving a shot hole type appearance.Spots may be surrounded by a yellow halo. Yellowing, leafdrop, and defoliation may occur in severe cases.

Control: The fungus can survive from year to year onSolanaceous weeds, so weed control is important. Leafmoisture from rains or dew increases disease severity.Fungicides may be used as recommended. Many commercialvarieties are resistant.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Gray Leaf Spot


Lesions on leaves appear as large watersoaked areas, thateventually turn brown and papery. Lesions may besurrounded by a white ring of mold if leaf wetness is high.Green to black irregular lesions are also present on thestems.

Control: The fungus develops during periods of cool wetweather. Fungicide sprays as a preventative measure duringthese periods may be needed if the crop is being grownnear large areas of tomato relatives (Solanaceous weeds,potatoes).

See




Bacterial SpeckCausal Agent: Pseudomonas syringae pv. tomato

Bacterial speck is widely distributed. Symptoms mayappear on any plant part. Leaves of infected plants arecovered by small, dark brown, irregular patches of necrotictissue that are surrounded by yellow halos. Diseaseseverity is increased by leaf wetness, from sprinklerirrigation, rain, or heavy dews.

Control: Minimize wetting of the leaves by using drip orfurrow irrigation. Copper sprays provide effective control.



Alternaria Canker(leaf symptoms)

Causal Agent: Alternaria alternata f. sp. lycopersici

Symptoms of Alternaria canker appear on stems, leavesand fruit. Large areas of the leaf lamina between veins iskilled, leading to leaf curling and eventual death of theentire leaf.

Control: Fungus overwinters in crop residue and is easilyspead by wind. Wounding of young plants (by mechanicaldamage or pruning) provides an entry site for infection.Furrow or drip irrigation is preferred over sprinklerirrigation. Preventative fungicide sprays may be required ifa "zero tolerance" for defects production system is needed.



Early BlightCausal Agent: Alternaria solani

Leaf symptoms of early blight are large irregularpatches of black, necrotic tissue surrounded by largeryellow areas. The leaf spots have a characteristic

concentric banding appearance (oyster-shell or bull's eye).

Control: Minimize wetting of the leaves by using drip or furrow irrigation. Infection occurs rapidlyduring periods of warm, wet weather. Fungicide sprays control the disease effectively.

See





Leaf symptoms of early blight are large irregular patches ofblack, necrotic tissue surrounded by larger yellow areas. Theleaf spots have a characteristic concentric banding appearance

(oyster-shell or bull's eye).


See




Leaf MoldCausal Agent: Cladosporium fulvum

Symptoms appear as light green patches on upper surfaces of older leaves. Underneath the leaves in theseareas, a purplish or olive-green patch of mold growth is visible. Infected leaves turn yellow and drop offthe plant.

Control: Fungus is spread is by wind currents. High humidity and warm temperatures encourage moldgrowth. The problem is especially severe in greenhouses, where adequate ventilation and air movementreduce disease severity by lowering moisture at the leaf surface. Fungicides are effective controls.

See


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/19.1,2.html [05/07/2001 02:21:20 p.m.]

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Leaf Mold

Tomato Leaf and Stem Disorders. Click on the photo that best matches problem you're trying todiagnose.

Tomato Leaf Disorders

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/tomleaf2.html [05/07/2001 02:21:30 p.m.]

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/leafcomp2.map

Leaf MinerDamageCausal Agent: Leaf Miner

Leaf miner larvae tunnelthrough the lamina of thetomato leaf eating thechlorophyll-rich mesophyllcells as they go. This leavesan irregular track of deadtissue that eventually causesthe leaf to stop functioning.

Control: Follow labelledrecommendations for thechemical control of leafminer.


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/lminer.html [05/07/2001 02:21:35 p.m.]

Salt DamageCausal Agent: Poor Water Quality

Excess salt accumulates in the tomatoplant in the older leaves. Leaves turnyellow, and will eventually fall off. Theplant is stunted and not vigorous, butother symptoms may be lacking.Tomatoes are relatively salt tolerant.

Control: Salt damage is rarelyencountered in field situations exceptunder very poor water quality situations.Salt damage may become a problem inpot culture or in hydroponics. Select salttolerant varieties.


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/salt.html [05/07/2001 02:21:44 p.m.]

Spotted WiltFruit are malformed, with raised yellow, red, andgreen mottled bull's eye rings. Plants from whichfruit are harvested are stunted, with older leavesturning yellow. Leaves show yellow speckling,with dark streaks along the petiole. Growing tips ofthe leaves may die. The virus is carried by flowerand onion thrips that have carried the virus frominfected weeds and ornamentals.

Causal Agent: Tomato Spotted Wilt Virus

Control: Elimination of plants that serve as hosts to thrips is the most important control measure. Cleancultivation, with special attention to border strips is important. Locate production away from large grainfields.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Spotted Wilt

Cucumber MosaicVirusVirus-infected plants are stunted, often with poorlyexpanded leaves. Plants are bushy in appearance.Leaves may be mottled, and often have a"shoestring" appearance. Fruit are small andmisshaped.

Causal Agent: Cucumber Mosaic Virus

Control: Aphids often are virus vectors, so anattempt to control the aphids is the first step.Eliminate weeds and remove infected plants fromthe field as soon as they are seen.


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/27.html [05/07/2001 02:21:55 p.m.]

PhosphorusDeficiencyPhosphorus deficiency is most oftenmanifested as purpling of the leaves,particularly the leaf veins. In severecases the whole plant may take on apurple hue. Tomato roots growing incold soil, either in the greenhouse or thefield, take up phosphorus poorly.Deficient plants lose vigor and yield

poorly.

Causal Factors: Cold Root Zone, Poor Fertility

Control: While phosphorus deficiency due to improper fertility may be a problem in hydroponic, potculture, and some sandy soil conditions, it is most likely a result of cool root zone temperatures. Plasticmulch will alleviate the problem in early field plantings, and a balanced liquid feed fertilizer willalleviate the problem in greenhouse and pot culture.


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomleaf/pdef.html [05/07/2001 02:21:59 p.m.]

PowderyMildewPowdery mildew is firstnoticed on older leaves as ayellow spotted appearance,that upon closer inspectionhas a whitish-gray powder onthe surface. The leaves willeventually die, but usuallyremain attached to the stem.The disease is worse underwarm, dry conditions.

Causal Agent: Leveillulataurica

Control: Sulfur dusts or wettable sulfur sprays are effective preventative controls. The establisheddisease will require one of the labelled mildew fungicides.



Septoria Leaf SpotCircular water-soaked lesions occur first on olderleaves. These spots eventually turn brown with graycenters and die, and if infection is severe enough,the entire leaf will die.

Causal Agent: Septoria lycopersici

Control: The fungus can survive in the debris fromprevious crops and/or weeds. Clean cultivation isimportant. The disease can be controlled by labelledfungicides.



Verticillium WiltOlder leaves on verticillium wilt-infected plants begin wiltingat leaf margins and turn yellow, then brown. Plants are stuntedand wilting is not alleviated by watering. A light tandiscoloration of the stem can be seen in cross section.

Causal Agent: Verticillium dahliae and V. albo-atrum

Control: The disease develops more rapidly in cool weather.The most effective control is planting one of the widelyavailable resistant varieties.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Verticillium Wilt

Tomato Stem Disorders. Click on the photo that best matches problem you're trying to diagnose.

Tomato Stem Disorders

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomstem/tomstem.html [05/07/2001 02:22:58 p.m.]

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomstem/stemcomp1.map

Alternaria Canker(stem symptoms)

Causal Agent: Alternaria alternata f. sp. lycopersici

Symptoms of Alternaria canker appear on stems, leavesand fruit. Large dark brown cankers form on stems;cankers may dry and split. These cankers will girdle thestem as they enlarge, killing the entire plant.

Control: Fungus overwinters in crop residue and is easilyspead by wind. Wounding of young plants (by mechanicaldamage or pruning) provides an entry site for infection.Furrow or drip irrigation is preferred over sprinklerirrigation. Preventative fungicide sprays may be required ifa "zero tolerance" for defects production system is needed.


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomstem/8.2.html [05/07/2001 02:23:02 p.m.]


Stem symptoms of early blight are brown,elongated, sunken lesions. These lesionscan occur anywhere on the stem or petioles,but are particularly severe if located at the

base of the plant as they may girdle the stem and kill the whole plant.


See




FusariumCrown RotCausal Agent: Fusarium oxysporumf. sp. radicis-lycopersici

Plants infected with crown rot arestunted and yellow. Symptoms beginon older leaves and progress to theentire plant. The entire planteventually turns brown and dies. Theroots are brown and may rot awaydue to secondary pathogens. Thestems often have brown vascularstreaks and dark brown lesions oftenoccur on the stem near the soil line.

Control: Infection enters the plant through wounds, but it may also be seed born. Disease development isfaster in cool wet soils, and the problem is often severe in greenhouse crops. Fungicide drenches may beeffective in the greenhouse situation.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Greenhouse Diseases

Fusarium WiltCausal Agent: Fusarium oxysporum f. sp. lycopersici

Fusarium wilt is distributed world wide; severalbiological forms (or races) of the pathogen are known.Leaves or whole branches wilt, turn yellow, then brownand die still attached to the plant (described as ayellow-flagging appearance). Sometimes half of a leafor branch will be affected, with the other half seeminglyunaffected. The fungus can be observed as browndiscoloration in the vascular tissue of affected branches.

Control: Infection enters the plant through the roots,and may be spread rapidly between plants in a field byirrigation. The best control in this case is prevention, byselecting varieties that are resistant to the disease.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Fusarium Wilt

Timber RotCausal Agent: Sclerotinia sclerotiorum and S. minor

Timber rot causes loss of plant vigor, followed by wilting andeventual death of the plant. Lesions on the stem show hollowpith when cut open, and white moldy growth is usually visibleat the edges of the lesions. Small black spherical fruitingbodies (sclerotia) are usually observed in or on the lesion.

Control: Sclerotinia occurs when tomatoes are planted aftersusceptible crops such as lettuce, cabbage, beans, peppers oreggplants. Soil sterilization is effective on a small plot basis,but good cultural practices and attention to sanitation and croprotation is important in the commercial setting.




Lesions on stems appear as large watersoaked areas, greento black in color, that eventually turn brown and dry up.Lesions may be surrounded by a white ring of mold if leafwetness is high.

Control: The fungus develops rapidly during periods ofcool wet weather. Fungicide sprays as a preventativemeasure during these periods may be needed if the crop isbeing grown near large areas of tomato relatives(Solanaceous weeds, potatoes).

See




Southern BlightCausal Agent: Sclerotium rolfsii

Southern blight causes a gradual wilting ofthe plant, and the plant eventually dieswithout changing color. The fungusgirdles the stem at the soil line and a largebrown irregular lesion is visible there. Thelesion is covered by a whitish mat offungus, and small, spherical, orange/tancolored fruiting bodies (scelerotia) arevisible on the lesion.

Control: High temperature and wet conditions promote the disease. Spores can survive in the soil forseveral years. Good sanitation (including removing and burning infected plants), extended crop rotations,and careful water management are key elements in controlling this disease.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Southern Blight

BroomrapeCausal Agent: Orobanche spp.

Broom rape is a parasitic flowering plantwith yellow/white stringy stems that usesthe tomato plant to produce its foodbecause it is not green and cannot conductphotosynthesis. Seeds germinate near thesoil line and the plant infects the rootsystem, gradually starving the tomato plant.This parasite is not widely distributed.

Control: Infected plants should beremoved from fields and destroyed.Fumigation of entire fields may benecessary to control severe infections.



Timber RotCausal Agent: Sclerotinia sclerotiorum and S. minor

Timber rot causes loss of plant vigor, followed by wilting andeventual death of the plant. Lesions on the stem show hollowpith when cut open, and white moldy growth is usually visibleat the edges of the lesions. Small black spherical fruitingbodies (sclerotia) are usually observed in or on the lesion.

Control: Sclerotinia occurs when tomatoes are planted aftersusceptible crops such as lettuce, cabbage, beans, peppers oreggplants. Soil sterilization is effective on a small plot basis,but good cultural practices and attention to sanitation and croprotation is important in the commercial setting.



Tomato Root Disorders. Click on the photo that best matches problem you're trying to diagnose.

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomroot/tomroot.html [05/07/2001 02:24:02 p.m.]

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomroot/rootcomp1.map

Damping OffCausal Agents: Pythium sp., Phytophthora sp.,Rhizoctonia sp. and others

Damping off is the term for a number of diseaseconditions that result in the infection and death ofyoung seedlings. A water soaked lesion is usuallyvisible on the stems near the soil line in the earlystage, but wilting and death of the seedling quicklyfollow.

Control: Seed germination in cool, damp soilpredisposes seedlings to infection. Overcrowdingand overwatering are complicating factors.Sterilization of seed beds, use of clean seedlinggermination medium, and careful attention towatering in the first two weeks of plant growthminimize losses. Fungicide-treated seeds mayreduce losses in the field.

See


http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tomroot/11.1.html [05/07/2001 02:24:07 p.m.]

http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Damping Off

Southern Bacterial WiltCausal Agent: Pseudomonas solanacearum

Rapid wilting of lower leaves, followed by wilting anddecline of the entire plant signals bacterial wilt. The leaves donot change color. A slimy, gray substance oozes from cutstems.

Control: Bacteria may infect plants from the soil or frominsect vectors. Proper field sanitation and crop rotation areeffective control measures. Use of disease-free transplants isimportant.



Corky RootCausal Agent: Pyrenochaeta lycopersici

Infected plants gradually decline and die when placed underthe stress of a fruit load. Growing points die back. Rootshave irregular, black, cracked lesions on them, and the rootsystem eventually dies.

Control: Corky root is most severe on greenhouse tomatoes,where the cool soil conditions favor its development andspread. Soil fumigation is the most effective control.

See




FusariumCrown RotCausal Agent: Fusarium oxysporumf. sp. radicis-lycopersici

Plants infected with crown rot arestunted and yellow. Symptoms beginon older leaves and progress to theentire plant. The entire planteventually turns brown and dies. Theroots are brown and may rot awaydue to secondary pathogens. Thestems often have brown vascularstreaks and dark brown lesions oftenoccur on the stem near the soil line.

Control: Infection enters the plant through wounds, but it may also be seed born. Disease development isfaster in cool wet soils, and the problem is often severe in greenhouse crops. Fungicide drenches may beeffective in the greenhouse situation.

See




Phytophthora Root RotCausal Agent: Phytophthora parasitica and P.capsici

Brown lesions develop on stems near the soil line.These lesions become brown and sunken, and willeventually girdle the plant resulting in wilting andrapid death. If the stem and tap root are cut lengthwise,a brown discoloration in the vascular tissue is evident.

Control: Water-logged or compacted soils promotethis disease. The best control is actually carefulattention to seedbed preparation. Avoid compactionand low spots that may accumulate water.



Southern BlightCausal Agent: Sclerotium rolfsii

Southern blight causes a gradual wilting ofthe plant, and the plant eventually dieswithout changing color. The fungusgirdles the stem at the soil line and a largebrown irregular lesion is visible there. Thelesion is covered by a whitish mat offungus, and small, spherical, orange/tancolored fruiting bodies (scelerotia) arevisible on the lesion.

Control: High temperature and wet conditions promote the disease. Spores can survive in the soil forseveral years. Good sanitation (including removing and burning infected plants), extended crop rotations,and careful water management are key elements in controlling this disease.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Southern Blight

Root KnotCausal Agent: Meloidogyne incognita, and otherMeloidogyne sp.

Infected plants are not vigorous, off color, andprogressively decline. The decline becomes rapidas the fruit load increases. Roots are swollen andcovered with galls.

Control: The root knot nematode is very difficultto control. Crop rotation with a non-susceptiblespecies is important, and avoiding plantingtomatoes after other highly susceptible species(cotton, okra) is a primary control. Many tomatovarieties are resistant, so variety selection is alsoimportant.

See



http://aggie-horticulture.tamu.edu/imagemap/mgmaps/tpdhveg6.html#Root Knot Nematodes

Southern BacterialWiltCausal Agent: Pseudomonas solanacearum

Rapid wilting of lower leaves, followed bywilting and decline of the entire plantsignals bacterial wilt. The leaves do notchange color. A slimy, gray substance oozesfrom cut stems.

Control: Bacteria may infect plants fromthe soil or from insect vectors. Proper fieldsanitation and crop rotation are effectivecontrol measures. Use of disease-free

transplants is important.



The Texas Plant Disease Handbook has moved.

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The Texas Plant Disease Diagnostic Laboratory hasmoved.

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Plant Pathology & Microbiology Home

Texas Plant Disease Handbook Has Moved

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The Texas Plant Disease Diagnostic Laboratory (TPDDL) was developed toassist clients in the identification of plant disease problems. The lab routinely workswith county Extension agents and specialists, homeowners, farmers, greenhouse andnursery producers, landscape contractors, interiorscapers, arborists, consultants, andany other group or individual needing accurate identification of plant diseaseproblems. The TPDDL strives to provide the most accurate and rapid plant diseasediagnosis together with recommendations for effective plant disease managementrecommendations.

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