Vegetables - Disease Management Pat Donald, MU (573) 882-2716 Om Sehgal, MU (573) 882-7060 KEY 1 = Symptoms 2 = Control TOMATO Seed decay and damping off (several fungi) 1. Pre-emergence death of seed & post-emergence death of seedlings. 2. Use hot water seed treatment: Soak seed at 122 degrees F for 25 minutes. Dry and apply Thiram (75WP) 1 teaspoon per pound of seed. Treatment also helps to control seed- borne bacterial spot, anthracnose and early blight. Damping off in seed bed or flats (several fungi) 1. Pre- or post-emergence death of seedlings. 2. Chlorothalonil (Bravo 720 or 90 DG). Foliar/Fruit Diseases of Tomato Anthracnose (fungus) Colletotrichum coccodes 1. Water soaked, sunken and circular spots on fruit, often with concentric rings. Spots vary from 1/4 - 1/2 inch in diameter. Infection begins on green fruit, but symptoms most apparent after ripening. 1. Apply fungicide spray at 7-10 day intervals throughout season, starting early when fruits of first cluster appear. Under severe disease conditions shorten spray interval. Use chlorothalonil (Bravo 720 2 pt./A or 90 DG 1 1/8-1 3/4 lb./A, or C/M 4-6 lb./A) or mancozeb (Dithane DF 1 1/2 lb./A, Dithane F-45 1.2-1.6 qt./A, Dithane M-45, Maneb 80 1 1/2 lb./A, Maneb + Zinc F4 1.2 qt./A, Manzate 200 DF 1 1/2 lb./A, Penncozeb and Penncozeb DF 1 1/2-2 lb./A, Maneb 75 1 1/2 lb./A, Ridomil/Bravo 81W 2 lb./A) or Kocide DF. Bacterial spot and speck (bacteria) Xanthomonas vesicatoria or X. campestris 1. Small, angular greasy spots on leaves and stems. On fruit, water-soaked spots are often surrounded by white holes in early stages. Later turn brown & are slightly sunken and scabby. 2. Plant clean seed and treat seed before planting (hot water soak 122 degrees F for two minutes). Dry and dust with Thiram at 1 tsp/lb. Use a three to four year crop rotation. Destroy diseased plant residues. Apply foliar sprays containing copper: fixed or neutral copper, copper hydroxide (Kocide DF) or fixed copper + streptomycin, Bravo C/M 4-6 lb./A, Ridomil/Copper 70W 1 1/2 lb./A. Early blight (fungus) Alternaria solani 1. Dark brown, circular spots with concentric rings on leaves. Spots on stem near ground line may cause girdling of young plants. Fruit spots are dark brown or black and leathery. Rots develop. 2. Rotate crops. Use disease-free plants. Use foliar fungicide applications every 7-10 days throughout season. Under severe disease conditions, shorten interval. Use fungicides under Anthracnose. Observe before harvest cut-offs, as specified on labels. Gray leaf spot or Stemphylium spot (fungus) Stemphylium solani 1. Small, brown spots with gray centers. Spot becomes shiny and usually remains small. Oldest leaves affected first and may drop off. 2. Use disease-free plants. Remove crop residues after harvest to reduce sources of infection for next year. Use fungicide program under Anthracnose. Bravo 500 2-3 pt./A. Late blight (fungus) Phytophthora infestans 1. Most serious in cool, wet weather. Large water-soaked brown to purplish irregular spots on leaves, petioles, and stems. A pale-yellow zone surrounds spots. Undersides leaves develop white mold growth in wet conditions. Fruit develop gray-green to dark brown water-soaked spots often near stem end. 2. Rotate crops. Remove plant residues. Use foliar fungicide program for Anthracnose, or Bravo 500 2-3 pt./A, Ridomil/Bravo 81 1 1/2 lb./A, Ridomil/Copper 70W 1 1/2 lb./A, Ridomil MA 58 1 1/2 lb./A. Be especially vigilant during periods of cool, wet weather. Reduce interval to four to five days. Septoria leaf spot (fungus) Septoria lycopersici 1. Small, water-soaked circular spots on leaves and stems. Spots have dark brown borders and gray center with small black fruiting structures. Leaves may die and drop off if heavily infected. 2. Rotate crops. Remove plant residues. Use foliar fungicide program as for anthracnose, early blight or late blight or Bravo 500 2-3 pt./A. Wilt Diseases/Disorders of Tomato Fusarium wilt (fungus) Fusarium oxysporum f.sp. lycopersicae 1. Leaves roll upward and wilt during hot part of day. Lower leaves turn yellow & drop off, progressing upward on stem until entire plant dies. Inner stem tissues have dark discoloration. 2. Use disease-free transplants. Use 5 year crop rotation, if possible. Use Fusarium wilt resistant varieties. Grower should consult seed catalogs for current information on resistant varieties. See statement on resistance classification at end of this section. Verticillium wilt (fungus) Verticillium spp. 1. Symptoms are similar to Fusarium wilt. Plants turn yellow and die quite rapidly. Vascular tissues have discoloration. Usually found under cool growing conditions, while Fusarium is more likely under hot growing conditions. 2. If possible, use long rotation once identified. Avoid planting tomatoes after peppers, potatoes, eggplant or raspberries. Verticillium is less likely than Fusarium, except in northern MO. Verticillium-resistant varieties are available. See resistance classification at end of this section. Walnut wilt (toxin-juglone-naphth-quinone) 1. Found in tomatoes grown in proximity to walnut trees. Plants wilt and die before mature, as a result of root contact with walnut roots or husks. 2. Do not plant tomatoes in root area of walnut trees. Plant other shallow rooted plant species in these areas. TOMATO NEMATODES Root-knot (nematode) Meloidogyne spp 1. Plant stunted and appear deficient in nutrients and water. Small to large galls on roots. 2. The homeowner may wish to relocate the garden or solarize the soil. Use a long crop rotation and plant resistant varieties. Consult seed catalogs for current information on resistant varieties. Select variety with "N" in designation. See statement on resistance classification below. Commercial growers may use Telone C-17. Root Lesion Nematode Pratylenchus spp. 1. For above-ground symptoms, see root-knot nematode. Reduced root growth. Lesions on roots. 2. Rotate crops. TOMATO VIRUSES Tobacco Mosaic Virus (TMV), Tomato mosaic virus (TMV, tomato strain) 1. Leaves mottled with light and dark green areas. May have distorted, narrow leaves. Other symptoms depending upon virus and/or virus combinations. 2. Use sanitation as a general virus control. Destroy infected plants. Destroy weeds that may harbor viruses. Avoid use of tobacco while working with young plants. Use TMV-resistant varieties. Consult the Plant Disease Clinic for more information on serological testing provided by Dr. Om Sehgal. Tomato spotted wilt virus (TSWV) 1. Caused by a virus that usually is spread by thrips. Foliage symptoms are similar to phenoxyl herbicide damage (thickened and malformed leaves). Fruit spots are about 1/2 inch wide, with numerous concentric rings. 2. Spotted wilt virus can overwinter in several weeds and ornamental plants. This virus is potentially very damaging. Great care should be exercised to avoid infection. Be very careful in avoiding bringing in the virus on transplants or ornamentals. Consult the Plant Disease Clinic for more information on serological testing provided by Dr. Om Sehgal. TOMATO NON-PARASITIC DISORDERS Blossom-End Rot (Ca-deficiency) 1. Caused by insufficient calcium and water stress when fruit are forming. Large dry brown to black, and often depressed, leathery areas at blossom end of fruit. 2. Usually, calcium deficiency results from low calcium level in soil, excessive nitrogen fertilization, rapid plant growth and drastic fluctuation in moisture. Add lime to soil and regulate soil moisture. Physiological and chemical injuries (herbicides) 1. Curling of growing tips, distortion of leaves. Veins close together. Can be confused with virus infections. 2. Determine whether herbicides were used in area. Tomatoes are very susceptible to 2,4-D herbicide. Plants may recover, depending upon material and exposure. Catface 1. Symptoms are extremely malformation and scarring, often associated with the blossom end. 2. Cool weather during fruit set and injury from 2,4-D herbicide may be involved with catface. Sunscald 1. Caused by sudden exposure of fruit to direct sunlight, particularly in hot dry weather. Most prevalent on green fruit. Whitish or yellowish patch on the side of fruit toward the sun. 2. Reduce the effects of defoliation by foliar diseases with appropriate fungicides. Internal Browning and Graywall (Blotchy ripening) 1. Affected green fruit has grayish brown blotches on the shoulders. Interal wall tissues are brownish. As fruit ripens, discolored blotches are yellowish on otherwise red fruit. 2. Causes of these disorders are not well established. Low light intensity, low temperature, excessive soil moisture, excessive soil compation, high nitrogen levels and low potassium levels have been suggested. A great deal of disease prevention with tomatoes can be achieved by planting VFN, VFNT, VFNTA, etc. disease-resistant varieties: V = Verticillium wilt resistance, F = Fusarium wilt resistance, N = Root-knot nematode resistance, T = tobacco mosaic virus resistance, and A = Alternaria or early blight resistance.