tomato fruit diseases disorders

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Tomato Leaf and Fruit Diseases and DisordersMegan Kennelly, Plant Pathologist

Kansas State University Agricultural Experiment Station and Cooperative Extension Service

Plant Pathology L-721

Septoria Leaf Spot and Early Blighthe fungal diseases Septoria leaf spot and early blight

are two of the most common tomatodiseases. Both diseases can occuranytime during the growing season,but they generally become more severeafter blossom-set. hese diseases resultin the formation of leaf spots that typ-ically develop first on the older leavesnearest the ground. During favorableconditions for disease development,these diseases can cause extensivedefoliation, resulting in sunscalding offruit and reduction in yield.

Septoria leaf spot and early blighthave similarities, but they can be distin-guished from one another in the field.

In Kansas, Septoria tends to bemore common than early blight.Symptoms of Septoria leaf spot firstappear as small, water-soaked spotson the lower leaves. Infection movesup the plant as the season progresses.

he leaf spots (lesions) generally aresmaller and more numerous than spotsresulting from early blight. Eventuallythe center portion of the Septorialesion turns light tan or gray, whilethe margin remains dark. Small black

fruiting structures (pycnidia) of thefungus, readily visible with a 10X handlens, form in the center portion of thelesion (Figure 1). Heavily infectedleaves may scorch and wilt, giving theplant the appearance of a wilt disease.

Early blight causes irregular, brownleaf spots (lesions) that range in sizeup to inch in diameter. he mostimportant diagnostic feature of early

blight is the formation of dark, concentric rings within thelesion, giving the spots a targetlike appearance (Figure 2).

Often, several lesions coalesce,causing the leaf to turn yellow,dry up, and fall off the plant.Defoliation weakens the plant

and exposes the fruit to sunscaldinjury. Although early blight isprimarily a foliage disease, lesionsmay develop on both stems andfruit. Fruit lesions are tan to brownleathery, and typically originate atthe stem end of the fruit.

CauseSeptoria Leaf Spot: Septoria

lycopersiciEarly Blight:Alternaria solani

Both fungi survive the winterin plant debris, on seeds, or on

weeds such as nightshade andhorse nettle. In the spring andsummer, spores of these fungi canbe splashed or blown to tomatoleaves. Relatively warm tempera-tures, abundant rainfall, and highrelative humidity favor diseasedevelopment.

ControlSanitation measures in the fall

reduce the amount of inoculumavailable for infection the follow-ing year. In the fall, deep plowtomato plots to bury tomato debrisor remove and destroy dead plants.

Avoid planting tomatoes in thesame area of the garden year after

Several tomato diseases and disorders cause leaf spots and fruit rots. ypically, these diseases do not kill the plants,but they can lead to significant yield and quality losses. Many disease-causing microorganisms can survive in plant debris,on seed, or in the soil. Proper sanitation is one of the best ways to prevent or reduce losses. Gardeners should remove all

tomato debris in the fall and avoid planting tomatoes in the same area year after year. his publication discusses some ofthe major leaf spot and fruit diseases and physiological disorders in Kansas. he first section describes fungal diseases, thesecond section describes bacterial diseases, and the third section describes physiological disorders.

Figure 1.Septoria leaf spot lesions often have

small black specks (fungal spore-producingstructures). Photo courtesy Wendy Johnson,Kansas State University.

Figure 2.Early blight lesions on tomatoleaves usually have a target-like appearance.Photo courtesy Clemson University - USDACooperative Extension Slide Series, Bugwood.org.

Fungal Diseases


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year. Clean seed and healthy transplants in the spring helpcontrol the disease. o reduce humidity and leaf wetness,avoid overhead irrigation. o improve airflow, use stakingand appropriate plant spacing. o prevent rain splash, usemulch. Avoid composting diseased plant material.

Start with the cultural practices described above. However,there are control materials available. For best results, beginapplications as soon as the symptoms become apparent.

Homeowners can refer to able 1. Commercial growersshould consult theMidwest Vegetable Production Guide forCommercial Growers; a management guide published every

year. Contact your local K-State Research and ExtensionOffice or the K-State Plant Diagnostic Lab for orderinginformation.

AnthracnoseAnthracnose is a frequent problem in the latter part of

the growing season on ripening tomato fruit. he diseaseresults in a fruit rot that reduces the quality and yield oftomatoes. Symptoms of anthracnose appear first as small,circular, slightly sunken lesions on the surface of ripeningfruits. he spots quickly enlarge, become bruiselike depres-sions, and develop a water-soaked appearance directlybeneath the skin (epidermis) of the fruit. Black, concentricrings form in the center of the lesions. he rings consist ofnumerous small fruiting structures (acervuli) of the disease-causing fungus (Figure 3).

During humid weather, masses of buff-colored fungalspores (conidia) are extruded from the fruiting structure.Several lesions coalesce, causing extensive decay of the fruit.Eventually, secondary microorganisms invade the lesions andcause a complete rotting of the fruit.

CauseAnthracnose is caused by several fungal species in the

genus Colletotrichum, including C. coccodes, C. dematium, andC. gloeosporioides.

he fungus can survive in infected plant debris andin the soil. Duringrainy weather, fungalspores are splashedonto the fruit. Mostinfection takes placeon ripe or overripe

fruit. Green fruitalso can be infected,although symptomsdo not develop untilthe tomatoes beginto mature. Diseasedevelopment isfavored by frequentrainfall temperaturesaround 80 degreesFahrenheit.

ControlSeveral cultural practices help reduce the incidence of

anthracnose. Mulching around the tomato plants preventssplashing of spores from the soil onto the fruits. Stakingtomatoes increases air movement and decreases the likeli-hood of favorable environmental conditions for infection.

Avoid overhead watering and remove infected or rottingfruits from the plant.

Start with the cultural practices described above.However, there are control materials available.Homeowners can refer to able 1. Commercial growers

should consult theMidwest Vegetable Production Guide forCommercial Growers; a management guide published every

year. Contact your local K-State Research and ExtensionOffice or the K-State Plant Diagnostic Lab for orderinginformation.

Table 1.Homeowner fungicides labeled for Septoria leaf spot, early blight and anthracnose of tomato.

Active ingredient Example products* Notes

Bacillus subtilis(biological controlorganism)

Serenade Garden DiseaseControl

Te bacterial species Bacillus subtilis has hadefficacy in trials for some fungi, but not in others.Little data available for tomato diseases.

chlorothalonil Fertilome Broad SpectrumFungicide, Ortho GardenDisease Control, Garden echDaconil Fungicide Concentrate

In trials with commercial formulations ofchlorothalonil, fungicides have reduced diseasecompared to untreated controls.

copper Natural Guard Copper SoapLiquid Fungicide

Performance of copper materials has been goodin several trials for Septoria and early blight, butpoor in several others.

maneb Hi-Yield Maneb GardenFungicide

In trials with commercial formulations of arelated material called mancozeb, fungicides havereduced disease compared to untreated controls.

*Labels change frequently, and it is the responsibility of the user to follow all label instructions.

Figure 3.Anthracnose causes circular, sunken areason ripening fruit which later support numerous fungalspore-producing structures (black specks). Photo courtesyClemson University - USDA Cooperative ExtensionSlide Series, Bugwood.org


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Bacterial Speck and SpotIn average Kansas summers, bacterial speck and bacte-

rial spot of tomato are not common, but they can causeserious damage during wet growing seasons. On tomatoes,

both diseases result in spot formation on the leaves andfruit. Heavy infection can cause defoliation, but the maineffect of these diseases is the reduction of fruit quality.

Leaf symptoms of bacterial speck and bacterial spotare similar. Both diseases cause small ( to inch) blacklesions on leaves. hese spots usually are surrounded bya yellow halo. he lesions of bacterial spottend to have agreasy appearance; those of bacterial speckdo not. he twodiseases are more easily distinguished by symptoms on thefruit. Bacterial spotresults in small, black, slightly raised,

water-soaked spots. hese spots may enlarge to inch indiameter and become very rough and cracked. Bacterial

specklesions also are slightly raised, but typically are muchsmaller ( inch) than those of bacterial spot. Bacterialspeck lesions do not crack or become scaly as in bacterialspot (Figures 4 and 5).

CauseBacterial SpeckPseudomonas syringae pv. tomatoBacterial SpotXanthomonas campestris pv. vesicatoria

Both bacteria can survive the winter on plant debris oron other weedy hosts. he bacteria also can be introducedinto a field on contaminated seed or infected transplants.Driving rain and mechanical injury to plants caused by hailand high winds increase the severity of these diseases. hedevelopment of bacterial speck is favored by relatively cool(65 to 75 degree Fahrenheit), wet conditions, while bacte-rial spot becomes more severe during periods of warmertemperatures (75 to 85 degree Fahrenheit), heavy rainfall,and high relative humidity.

ControlControl measures for the two diseases are similar.

Removing plant debris in the fall, cultivation of weeds,rotation, and the use of clean (noninfested) seed and trans-plants reduces the severity of or prevents these diseases. oreduce humidity and leaf wetness, avoid overhead irriga-tion. Use staking and appropriate plant spacing to improveairflow. Use mulch to prevent rain splash. Do not work inthe tomato planting when plants are wet.

Start with the cultural practices described above.here are several copper-based compounds available forhomeowners, but chemical control of bacterial diseasesis inconsistent. Bacteria have extremely fast reproductivetimes, and it is difficult to manage an epidemic once it is

underway. If you use a chemical, read and follow all labelinstructions.

Commercial growers should consult theMidwestVegetable Production Guide for Commercial Growers; a

management guide published every year. Contact your localK-State Research and Extension Office or the K-StatePlant Diagnostic Lab for ordering information.

Bacterial CankerBacterial canker, a third bacterial disease, can be a

serious problem in commercial and small garden tomatoplantings. his disease can cause lesions or cankers on anyportion of the plant, including the fruit, or it can result ina general wilt or decline of the plant. Diseased tomatoesfirst exhibit yellowing and wilting of leaves on a portion of


BACTERIAL DISEASES

Figure 4.Bacterial speck causes tiny black lesions on fruit.Photo courtesy Christine Smart, Cornell University.

Figure 5.Bacterial spot causes lesions up to inch that areoften rough or cracked in appearance. Photo courtesy Mary

Ann Hansen, Virginia Polytechnic Institute and StateUniversity, Bugwood.org.

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the plant. he leaves eventually become brittle and dry, anddrop from the plant. Yellowish streaks may develop on leafpetioles, stems, and also internally in the water-conductingtissue of the main stem. Rotting in the stem may be visible

when stems are cut (Figure 6). In addition, small circulardepressed areas called cankers may form on the stem.

he most diagnostic feature of bacterial canker is theformation of fruit spots. hese spots may be confused withthose caused by bacterial speck or spot. However, fruitlesions caused by bacterial canker are bordered by a distinct

white halo (Figure 7). hese white halos may disappear asthe fruit ripens.

CauseClavibacter michiganensis subsp. michiganensis

he bacterium can be introduced into fields on con-taminated seed or on infected transplants. he bacteriumalso can survive in soil on infested plant material for atleast 1 year. During the growing season, the small bacteriaare dispersed by water (irrigation or rain) and infect plants

through wounds or natural openings. Once inside the plant,the organism can invade the water-conducting tissue andbe carried systemically throughout the plant.

Figure 6.Bacterial canker can cause a rotting in the stem,visible as discoloration when the stem is cut. Photo courtesyPaul Bachi, University of Kentucky Research & EducationCenter, Bugwood.org.

Figure 7.Bacterial canker lesions on fruit usually have awhite halo. Photo courtesy Mary Ann Hansen, VirginiaPolytechnic Institute and State University, Bugwood.org.

Disease development is favored by moderately hightemperatures (75 to 85 degrees Fahrenheit) and wet, humidconditions.

Controlhe most important means of controlling bacterial

canker is using clean seed from a reputable firm and trans-planting into disease-free soil. If you have an outbreak ofbacterial canker, do not plant tomatoes or other crops in the

tomato family (pepper, eggplant, potatoes) into that bed forat least 3 years. Avoid overhead irrigation, which spreadsbacteria and allows infection to occur. Avoid working withplants under wet conditions. Sanitize tools such as pruningshears. Use mulch to prevent rain splash.

Start with the cultural practices described above.Copper materials are available but are generally noteffective.

Commercial growers should consult theMidwestVegetable Production Guide for Commercial Growers; amanagement guide published every year. Contact your localK-State Research and Extension Office or the K-StatePlant Diagnostic Lab for ordering information.


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Blossom End RotFruits develop a sunken, water-soaked lesion near the

blossom end. he lesion expands rapidly, turns black, andresults in a flattening of the end of the fruit (Figure 8).

Secondary organisms frequently invade the lesions andcause a complete rotting of the fruit. he disorder com-monly occurs during periods of hot, dry weather.

Cause: PhysiologicalBlossom end rot is a physiological disorder (not an

infectious disease) resulting from a shortage of availablecalcium in rapidly developing fruit. his problem canoccur even though the soil has an abundance of calcium.

he disorder is associated with rapid plant growth andquick fluctuations in soil moisture. In Kansas, the diseaseis typically most severe during periods of hot daytime

temperatures, low humidity, and windy conditions. hedisease also is more serious when excess nitrogen fertilizerhas been applied.

ControlProviding even and adequate soil moisture, especially

during fruit set, can reduce the incidence of blossomend rot. More uniform soil moisture can be achieved bymulching and a balanced irrigation program. Avoid over-fertilization of the plant with nitrogen, especially of theammonia formulation. Select cultivars that are less prone toblossom end rot.

Leaf RollDuring mild spring weather, top growth is more

vigorous than root growth. When drier summer weatheroccurs, the abundant foliage transpires water faster than theroot system absorbs it. he plant compensates by rollingits leaves to reduce surface area (Fig. 9). he leaves maybecome thickened. he symptoms may occur after cultiva-tion, heavy rains, or a sudden change in weather.

Controlhe condition is temporary and the plant will recover

on its own. o prevent leaf roll, keep soil evenly moist (nottoo wet, not too dry) and avoid cultivation that damagesroots.

Growth CracksGrowth cracking occurs on tomato fruit that expand

too quickly. It is most common on nearly ripe fruit, but itcan occur on younger fruit. Cracks develop in concentriccircles around the stem scar (Figure 10). hey also can

PHYSIOLOGICAL DISORDERS

Figure 8.Blossom end rot causes sunken, water soakedlesions that eventually turn black. Photo courtesy David B.

Langston, University of Georgia, Bugwood.org.

Figure 9.Physiological leaf roll. Photo courtesy WardUpham, KSU Horticulture

Figure 10.Concentric growth cracks. Photo courtesy PaulBachi, University of Kentucky.


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L-721 May 2009

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Publications from Kansas State University are available on the World Wide Web at: www.ksre.ksu.edu

Contents of this publication may be freely reproduced for educational purposes. All other rights reserved. In each case,credit Megan Kennelly, Tomato Leaf and Fruit Diseases and Disorders, Kansas State University, May 2009.

occur as radial cracking that spreads in a starlike patternfrom the stem scar toward the blossom end (Figure 11).

Cause: PhysiologicalGrowth cracks occur when the fruit expands and

stretches the epidermis (skin) beyond its capacity (Figure10). Excessive moisture, fluctuations in temperature, and anoverabundance of nitrogen can cause cracking. In addi-tion, tomato fruits exposed to sunlight are more prone to

cracking.

ControlSelect cultivars less prone to cracking. Provide even

water and balanced nutrition to avoid overly lush growth.Limit fruit exposure to sun through proper staking or trel-lising, and by managing foliar diseases.

References:Caldwell, B., Rosen, E. B., Sideman, E., Shelton, A., and

Smart, C. 2005. Resource guide for organic insect anddisease management. New York State AgriculturalExperiment Station, Geneva NY.

Jones, J.B., Jones, J. P., Stall, R. E., and Zitter, . A. 1991.Compendium of omato Diseases. he AmericanPhytopathological Society, St. Paul MN.

Midwest Vegetable Production Guide for CommercialGrowers, 2008. Available online at: www.btny.purdue.edu/Pubs/ID-56

Raudales, R. E. and McSpadden-Gardener, B. B. 2008.Microbial biopesticides for the control of plant diseasesin organic farming. he Ohio State University, publica-tion HYG-3310-08. Available online at: ohioline.osu.edu/hyg-fact/3000/pdf/HYG_3310_08.pd

Figure 11.Radial growth cracks. Photo courtesy Meg

Williamson, Clemson University.

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