Tomato Production Guide for Florida: Disease Control ( Publisher's URL )

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Tomato Production Guide for Florida: Disease Control
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Fact sheet
Pernezny, K.
University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
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Gainesville, Fla.
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Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
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"August 1997"
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"SP 214"

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University of Florida Institutional Repository
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University of Florida
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1.This document is a chapter of SP 214, last printed in 1990 as Circular 98 C. SP 214 ,Tomato Production Guide for Florida, l ast printed in 1990 as Circular 98 C, is a publication of the Commercial Vegetable Guide Series, Florida Cooperative Extension Service, Institute of Food and AgriculturalSciences, University of Florida. Publication date: August 1997. For more information about how to order the complete print document, SP 214, call UF/IFAS Distribution at (352) 392-1764. Please visit the FAIRS Website at The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Servi ce office. Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / Christine Taylor Waddill, Dean. 2.K. Pernezny, professor, Everglades-REC, Belle Glade, Cooperative Extension Service, Institute of Food and Agricultural Scienc es (IFAS), University of Florida, Gainesville FL 32611. The Tomato Production Guide for Florida is edited by G.J. Hochmuth, professor, Horticultural Sciences Department, IFAS. SP-214Tomato Production Guide for Florida: Disease Control1K. Pernezny2Tomatoes are subject to attack from many disease-causing organisms including fungi, bacteria, and viruses. In addition many physiological disorders can cause serious losses in tomato crops. Below is a general description of the major tomato diseases. For specific chemical control measures, consult the tomato disease control chart in the Disease Control Guide. This information is available in hard copy or electronic format through the County Extension Office; the Florida Cooperative Extension Service; Extension Circular SP-170, Commercial Vegetable Production Guide for Florida; and the Tomato Scouting Handbook.Major Tomato DiseasesBacterial Soft Rot. This disease is caused by a bacterium, Erwinia carotovora subsp. carotovora which infects stems, petioles, and fruits. On the fruit, small water-soaked spots appear which enlarge rapidly, converting the fruit into a soft, watery mass. The disease is particularly troublesome in storage or shipping. Control of the disease involves procedures which minimize wounding of fruit during harvesting and packing. Follow correct washing procedures using chlorinated water.Bacterial Speck. Caused by Pseudomonas syringae pv. tomato this disease is often difficult to distinguish from bacterial spot since both diseases can occur simultaneously. Bacterial speck lesions appear as numerous, tiny, dark brown spots less than one-sixteenth of an inch in diameter and usually do not penetrate deeper than the fruit epidermis. Speck lesions are usually smaller than spot lesions and do not exhibit the raised, scab appearance of spot lesions. Since this disease is seed borne, control of speck begins with disease-free seed and transplants. Control of speck in the field is difficult. Destroy tomato plant residues and avoid double-cropping.Bacterial spot. This disease is caused by Xanthomonas campestris pv. vesicatoria This disease is one of the most devastating diseases in Florida and can often be confused with young early blight or gray leaf spot lesions. Bacterial spot lesions on leaves are brown, irregularly shaped, and greasy in appearance. They are rarely more than 1/8 inch in diameter. Spots lack the concentric ring appearance of early blight and are less uniformly distributed than gray leaf spot. Small, watersoaked spots appear on fruit which are slightly raised and 1/8 to 1/4 inch in diameter. There may be a slight halo around the spot which eventually disappears leaving a scabby lesion.


Tomato Production Guide for Florida: Disease Control Page 2 February 1998Leaf infection occurs through natural openings while wounds are common entries for fruit infection. Bacterial spot is difficult to control in the field, so care must be taken to avoid purchase of infected transplants. Destroy the old crop residue once harvest is complete, and keep volunteer tomato plants out of fallow land. Preventative copper and maneb sprays are used to control mild outbreaks in the field. Avoid excessive use of copper, since it can be toxic to plants and can build up to toxic levels in the soil. Consult Plant Pathology Fact Sheet No. 3 for more information.Bacterial wilt. Caused by Pseudomonas solancearum this disease is distinguished from fusarium and verticillium wilts by the rapid wilt, lack of foliage yellowing, and hollowness of stems. Stems cut from plants with bacterial wilt exude a graybrown, flowing material from the cut. The bacteria enters the plant from various types of wounds to the roots. To control bacterial wilt, avoid planting in low, wet areas or on land with a history of bacterial wilt. Rotate fields to nonsolanaceous crops. Fumigation of seedbed and field may help where the disease is anticipated. Avoid movement of machinery or water from infested fields to noninfested areas.Black shoulder. On fruit approaching maturity, dark gray-to-black areas appear on the shoulders. These areas become leathery and often sunken. The cause of the problem is not known but is worse in cool, rainy weather, and affects some cultivars more than others. The only practical method of control is to use cultivars which are tolerant of this problem.Blossom-end rot. This disorder is a physiological problem caused by calcium deficiency and water stress. The blossom-end of the fruit collapses and shrivels to a leathery, dark, dry rot. Conditions which limit calcium availability to the fruit lead to blossom-end rot. These include acidic soils, droughty soils, and flooded soils. Calcium moves in the water stream, in the plant, so it does not move preferentially to fruit, but to leaves. Excessive N can lead to excessive vegetation and encourage low calcium transport to fruits. To control the problem avoid those conditions listed above. Follow a program of soil testing and careful water management. Foliar fertilization with calcium is difficult because it requires many applications of calcium, each in small amounts, to provide enough calcium to youngest plant parts and usually will not cure blossom-end-rot.Buckeye rot. A disease caused by Phytopthora parasitica, affects fruits which are on or near the ground. Infected spots enlarge in a series of irregular, concentric bands. To control buckeye rot, provide good field drainage, and grow the crop using stakes and plastic mulched beds which reduce fruit contact with soil.Damping-off. Caused by several fungi, this disease affects young seedlings in the transplant bed or shortly after setting in the field. Seedlings wilt, fall over, and usually cause damage to the stem. Direct-seeded crop stands also can be reduced by direct attack to the germinating seeds especially in cool, damp soils. To control the disease, start with fungicidetreated seed and soil fumigation. Maximize soil drainage and use plastic mulch to increase soil temperature. For more information, see Plant Pathology Fact Sheet No. 1.Early blight. The causal organism, Alternaria solani can infect all above ground portions of the plant. On the leaves, small, brown lesions enlarge to irregular spots which consist of a series of concentric rings. Similar lesions can develop on stems. Fruit is usually infected near the calyx in the green or ripe stage. Lesions are black, sunken, irregular in shape and have a characteristic concentric ring appearance. The most effective control measure is to follow a fungicide application schedule in the seedbed and field. For more information, consult Plant Pathology Fact Sheet No. 7.Fusarium wilt. Two f. sp. of the organism Fusarium oxysporum f. lycopersici have been found in Florida. The disease first appears in the field as yellowing of older leaves. This occurs on one side of the leaves and on one side of the plant. Eventually


Tomato Production Guide for Florida: Disease Control Page 3 February 1998the whole plant wilts and dies. The vascular tissue of diseased plants is dark brown in color, especially near petiole scars. To control wilt, use resistant varieties where possible. Maintaining a soil pH near 6.5 will reduce the severity of fusarium disease.Fusarium crown rot. This disease is caused by the fungus Fusarium oxysporum f. sp. radicislycoperici. The symptoms are distinct from the classic Fusarium wilt. Marginal chlorosis occurs on oldest leaves at about the time of maturity of the first hands of fruit. Wilting follows. Vascular discoloration is evident in lower stems and/or roots. The pith is necrotic at the soil line, often with external cankers or lesions on the stem from the soil line upward. Adventitious roots may develop on lower stems of infected plants. There may be an aerial phase to this particular Fusarium disease. Fumigation seems to provide some control of Fusarium crown rot. Rotation away from tomatoes may be necessary on fields with a recurring crown rot problem.Gray leaf spot. The lesions from Stemphylium solani begin as small brown-black specks on lower leaves and enlarge to about 1/12 inch in diameter. They become lighter in color and shiny in appearance, with yellow borders. Eventually leaves become yellow and drop. To control, carefully destroy old crop refuse, especially if gray leaf spot was a problem the preceding year. Most cultivars presently used in Florida have resistance to gray leaf spot. The disease is usually observed on cherry tomatoes where resistance is less common.Gray mold. This disease, caused by Botrytis cinerea is characterized by large, water-soaked lesions which are usually covered with grayish mycelium. This organism can enter leaves and fruits through any opening or wound. On fruit, a watery lesion with a tan center appears and eventually leads to a soft rot. Occasional aborted fruit infections will appear on the fruit. These lesions, called ghost spots, consist of a cloudy white ring 1/16 of an inch in diameter with a dark speck in the center. Gray mold does not develop where soil pH is 6.5, or on naturally calcareous soils. Fungicides can be used as needed.Gray wall and blotchy ripening. The exact cause of these diseases, which are considered by some to be different disorders, is not fully understood. Dark-colored tissue sometimes develops in the fruit wall, and areas of the fruit fail to develop proper color, often remaining gray or yellow. In laboratory studies, symptoms similar to those of gray wall were duplicated by bacteria infiltration of the fruit, but under field conditions, bacteria cannot be isolated from affected fruits. Both disorders seem to increase in severity with K deficiency and seem to be worse under high N in the winter.Late blight. Caused by Phythopthora infestans this disease results in large, irregular, greenish watersoaked areas on fruits. The lesions enlarge rapidly, become brown, and have a wrinkled surface. Stem lesions can girdle the plant, causing death. The disease is most prevalent during cool and moist weather conditions. To control late blight, apply fungicides based on scouting reports. Avoid rotating tomatoes with potatoes. For more information, consult Plant Pathology Fact Sheet No. 6.Leaf mold. This disease caused by Cladosporium fulvum is favored by moist conditions and reduced aeration. Leaf mold can be severe in greenhouses. Symptoms appearing first on the lower leaves consist of yellowing in spots on the upper leaf surface with olive-green mold on the corresponding area on the underside of the leaf. To control leaf mold, provide adequate aeration with proper plant spacing and choose resistant varieties. Apply fungicides when needed.Phoma rot. This causal organism, Phoma destructiva can infect most above-ground portions of the plant. On leaves and stems, small black lesions enlarge to spots which are irregular in shape, slightly sunken, and zonate as in early blight. The fruiting bodies of the fungus can be observed in the lesions with a hand lens. On fruit, lesions are associated with


Tomato Production Guide for Florida: Disease Control Page 4 February 1998injuries and are distinguished by the black color and the small fruiting bodies. For control, use only fungicide-treated seed and employ a fungicide spray program in the seedbed and field.Pith necrosis. This disease is caused by the bacterium Pseudomonas corrugata The first symptoms noted are chlorosis of young leaves, followed by wilting of plants. Lower parts of infected stems may show brown lesions on the outside. The best diagnostic feature is the hollow or laddered pith revealed when a longitudinal cut is made in the lower stem. Profuse development of adventitious roots takes place in the area of moderate to severe pith degradation. The bacterium is probably soilborne. The disease usually is most severe in cool temperature, with rainy conditions.Potato Y virus. This disease causes young leaves to curl inward and downward giving the plant a drooping appearance. The tip leaflet usually contains dark brown dead areas. Stems often show a purple streaking but fruits do not have symptoms. Infected plants become stunted and yield is reduced. The virus is transmitted by aphids from various weed hosts, such as nightshades and ground cherry, and from infected potato fields. To control the virus, eradicate weed hosts and avoid planting tomatoes near potatoes. Application of stylet oils might help reduce the virus spread by aphids.Pseudo curly top. This is another virus disease, which is most prevalent on younger plants. The leaves curl upward with the veins becoming purple. Branches and stems become stiff and brittle. To control this disease, destroy nightshade and ragweed. Sometimes insecticide sprays of the field perimeter are needed to destroy tree hoppers which transmit the virus.Sclerotinia stem rot. The organism, Sclerotinia sclerotiorum can cause a damping-off seedling disease but more commonly attacks older plants in the field. The fungus attacks plants at the soil line producing a canker lesion on the stem which is covered with white mycelium. The plants wilt and die. Stems reveal cavities filled with black sclerotia or resting bodies of the fungus when cut open. Control can be achieved through flooding but this action carries with it the risk of spreading other diseases such as bacterial wilt. Use well drained fields, sanitation, and crop rotation. Avoid following crops, such as beans, celery, lettuce, or other crops that have been infected with this organism. Proper fungicides applied to the seedbed or field may be used. For more information, consult Plant Pathology Fact Sheet No. 22.Soil rot. This disease, caused by Rhizoctonia solani causes fruit rot by penetrating wounds or undamaged epidermis wherever the fruit contact the soil. The lesions are similar to buckeye rot. However, soil rot lesions develop slowly and do not lead to soft rot as in buckeye rot. To control soil rot, grow the tomato crop on stakes using plastic-covered beds. Apply fungicides when needed and prevent losses in transit by careful grading.Solar yellows. This physiological disorder results in fruits with shoulders that remain bright yellow. It is caused by high fruit temperatures and high light intensity which prevent proper red coloration of the fruit. It can be serious during extended hot and dry periods. To control this disorder, maintain proper foliage coverage of fruit by good disease management, fertility levels, and irrigation. Where plant foliage coverage is not satisfactory, some success in control has obtained by spraying clay suspensions on the fruits in the field which then washes off in the packing house. This practice has not been fully researched so it should be tried only on a trial basis.Southern blight. This causal fungus, Sclerotium rolfsii attacks mature plants just below the soil surface completely girdling the stem causing rapid wilting and death. The mycelium grows over the diseased areas and the soil surface forming a mat with tan, mustard-seed-sized sclerotia. Fruit near the ground are often attacked.


Tomato Production Guide for Florida: Disease Control Page 5 February 1998Control begins with disposal of infected plants to prevent spread. Use staking culture practices to keep fruit off the ground and employ soil fumigants prior to planting. For more information, see Plant Pathology Fact Sheet No. 4.Target spot. This disease, caused by Corynespora cassicola begins on the leaf as small brown spots which become surrounded by a sunken, dull green area. The center of the spot may become white on older leaves. Fruit rot on the shoulder or sides of fruit begins as small white spots with a border and enlarge up to inch. To control target spot use approved fungicides.Tobacco etch. This virus disease is similar to potato Y virus except the plants with etch are more stunted and the virus spread is slower. Laboratory assays are needed for a definite diagnosis. To control tobacco etch, eradicate weed hosts, such as nightshades and ground cherry. Insecticides and stylet oil applications to reduce the aphid vector, might help.Tobacco mosaic. This virus, also called tomato mosaic, causes plant stunting if plants are infected early but usually little stunting is observed in later infections. The leaves are usually mottled and crinkled. The fruit can have symptoms consisting of mottling, rough surfaces, and occasional fruits with opening in the walls. The virus is highly infectious and readily transmitted by any physical contact with plants. Workers should wash hands in 70 percent alcohol or with strong soap to remove virus particles. This is especially important for workers who use tobacco products. Eliminate volunteer tomato plants and cleanse equipment that comes in contact with infected plants between seasons.Tomato mottle virus. Leaves show bright yellow mottling on upper leaves, upward cupping of middle and lower leaves, and reduction in leaflet size. Stunting of plants can be quite severe. This is the common gemini virus that has caused severe damage to the states tomato industry in recent years. The virus is vectored by the silverleaf whitefly. Plants left in the field act as a bridge supporting whiteflies and virus for subsequent crops. It is imperative that crops be destroyed promptly. Insecticides, especially systemics applied at planting, can be effective in management of whiteflies and the tomato mottle virus.Tomato spotted wilt. This is a virus disease. Very characteristic bronze discoloration of young leaves is seen. There is dieback of terminal branches and often a rather distinctive purple streaking of distal portions of stems and petioles. Plants may be stunted. Leaves may curl and drop downward, giving the plant a wilted appearance. An important diagnostic feature is the appearance of brownish, concentric rings on green fruit. The tomato spotted wilt virus is vectored by several species of thrips. It has traditionally been more of a problem in northern Florida.Tomato yellows. Plants infected with this virus have a general chlorotic appearance. Fruit do not show symptoms. The virus is spread by aphids from weed hosts such as nightshade, ground cherry, and Datura species. To control tomato yellows, maintain a careful weed control program and reduce aphid populations with insecticides.Verticillium wilt. This disease is caused by the fungus Verticillium albo-atrum The disease starts with wilting of the lower leaves. Eventually leaves develop yellow areas along the margins and die. The disease does not rapidly kill the plant but results in severely reduced yields. The interior of the stem, near the base of the plant, will reveal a tan discoloration of the vascular tissue which does not extend up the stem as far as fusarium wilt does. Also the stem cavity does not become hollow as in bacterial wilt. Control of verticillium wilt can be achieved with resistant varieties. In the seedbed and the field practice sanitation, rotation, and fumigation.Minor tomato diseases. Other diseases which can occasionally appear include black mold


Tomato Production Guide for Florida: Disease Control Page 6 February 1998Alternaria fasciculata nailhead spot Alternaria tomato anthracnose Colletotrichum phomoides bacterial canker Corynebacterium michiganense pv. michiganense, fruit rot Geotrichum candidum and septoria leafspot Septoria lycopersici.