Tomato Diseases Fungal Bacterial Viral Fruit Anthracnose - Colletotrichum spp. Fusarium Wilt - Fusarium oxysporum Verticillium Wilt - Verticillium dahliae, V. albo-atrum Early Blight - Alternaria solani Late Blight - Phytophthora infestans Septoria Leaf Blight - Septoria lycopersici Soil Rot of Fruit - Rhizoctonia Bacterial Bacterial Spot - Xanthomonas campestris pv. vesicatoria Bacterial Speck - Pseudomonas syringae pv. tomato Viral Cucumber Mosaic Virus

Fusarium Wilt Fusarium is a soil-inhabiting fungus that invades the vascular system of the plant and interrupts the passage of nutrients and water to the above-ground parts, causing wilting symptoms.

Fusarium Wilt The vascular tissue in this slide is discolored due to infection by the Fusarium fungus. Healthy vascular tissue is white to light green.

Fusarium Wilt This slide shows the Fusarium fungus growing out of the infected stem tissue in a laboratory test.

Verticillium Wilt Verticillium is another soil-inhabiting fungus that causes a wilt in tomato. Symptoms are quite similar to those of Fusarium wilt. A laboratory test is necessary for positive diagnosis.

Tomato Diseases - Fusarium and Verticillium Wilts - Key Points Pathogens: Fusarium oxysporum, Verticillium dahliae, V. albo-atrum Soil-borne pathogens Survive in soil for several years Plants generally infected through roots

Tomato Diseases - Fusarium and Verticillium Wilts - Control Strategies Rotation (at least 2-3 years) VF or VFN resistance

Septoria Leaf Spot This is an extremely destructive foliage disease of tomato. Symptoms begin on the foliage closest to the ground and then move on up the plant. Wet, humid weather increases the severity of the disease that can progress to the point where all the foliage is killed and all that is left are green or ripe fruit exposed to the sun.

Septoria Leaf Spot Leaf spots tend to be circular, with dark borders and gray or tan centers. With the use of a hand lens one can see the small black pycnidia in the center of these lesions. These pycnidia produce the fungal spores, that serve as inoculum that attack new leaves.

Tomato Diseases - Septoria Leaf Blight Key Points Pathogen: Septoria lycopersici Survives over winter on infected plant debris, and also on equipment, stakes and cages Spores dispersed by splashing water (rain, irrigation), workers or equipment moving through wet plants Favored by moist, warm weather Symptoms generally appear first on lower leaves

Tomato Diseases - Septoria Leaf Blight Control Strategies Rotation (at least 1-2 years) Thorough sanitation of equipment, stakes, etc. Stake plants Plastic mulches Fungicide sprays Several effective fungicides available Apply at least weekly when weather favorable for disease Good coverage, especially of lower leaves, crucial Carefully read label directions

Early Blight This disease is similar to Septoria blight but is caused by the fungus Alternaria. It too starts on the lower foliage and can completely defoliate the plant.

Early Blight The leaf lesions of this blight are more uniformly brown without the light center as found with Septoria. Yellowing of the leaf tissues surrounding the lesions is due to a toxin produced by the pathogen.

Early Blight A closer look at the lesions show the characteristic target-like pattern. The fungus sporulates on all the parts of the necrotic tissue. Lesions generally do not cross over major veins, but may coalesce to form larger dead areas on leaflets.

Tomato Diseases - Early Blight Key Points Pathogen: Alternaria solani Survives on infected plant debris - partially buried debris is an excellent source of inoculum Spores wind dispersed, can be carried long distances Greatest threat of infection: Fields with short rotations Planting adjacent to fields infected previous year where debris not completely buried Infection occurs first on oldest leaves

Tomato Diseases - Early Blight Control Strategies Plant rotation - minimum of at least 2-3 years between solanaceous crops Potato, tomato, weeds in nightshade family excellent hosts Completely bury plant debris after harvest Fungicide applications Several effective fungicides available Carefully read label directions Provide adequate nitrogen Avoid excessive irrigation

Late Blight This disease is caused by the same pathogen that causes late blight in potato; Phytophthora infestans. Leaf infections are manifested by irregular lesions that initially appear water-soaked, becoming darkly necrotic and spread rapidly to cover large areas. During humid weather, one can observe the cottony mass of fungal hyphae extruding out of the stomates on the lower surface of the leaflet along the edge of the lesion margin when necrotic tissue meets healthy tissue.

Late Blight Tomato fruit infected with the late blight fungus exhibit dark greasy and roughened areas of the fruit skin (epidermis).

Tomato Diseases – Late Blight Key Points Pathogen: Phytophthora infestans Same fungus that causes late blight of potato Isolates may differ in ability to infect potato and tomato Both mating types (A1 and A2) are now found in WI Symptoms: Lesions on leaves initially water-soaked spots with irregular borders Lesions turn pale green, then brown to almost black White fungal growth appears on underside of leaves at border between necrotic and healthy tissue Petiole and stem symptoms similar – lead to rapid death of plant

Tomato Diseases – Late Blight Key Points Source of inoculum: Cull piles of infected potatoes or tomatoes Infected tomato transplants Infected plants in neighboring fields Hairy nightshade Favored by rain, high relative humidity Control Strategies Destroy cull piles, and weed hosts Plant disease-free tomato transplants Protectant fungicides – several effective fungicides available

Fruit Anthracnose While infection can occur while the fruit is still green, symptoms do not appear until the color change occurs and the fruit begin to soften. Fruit lesions are circular and slightly sunken, as if someone pressed one’s finger against the ripening fruit.

Fruit Anthracnose As the lesions enlarge, black microsclerotia form in the bottom of the lesion. Under moist conditions the lesions may be covered with masses of pink-colored spores. Secondary organisms can invade the tissue enhancing the breakdown of the fruit.

Tomato Diseases - Fruit Anthracnose Key Points Pathogen: Several species including Colletotrichum coccodes, C. dematium and C. gloeosporioides Favored by wet weather and warm temperatures Survives in soil and plant debris several years Spores splashed by rain or irrigation onto foliage and fruit Ripe or overripe fruit most susceptible, symptoms progress rapidly

Tomato Diseases - Fruit Anthracnose Control Strategies Rotation (at least 2 years) Weed control (eliminates alternate hosts) Stake plants Mulches Optimum plant spacing Remove and destroy infected fruit Fungicide sprays

Tomato Diseases - Fruit Anthracnose Control Strategies Fungicide sprays Several effective fungicides available Start when first fruit reaches size of a quarter Continue weekly until harvest Read labels carefully Examples of label requirements: rate of application seasonal use limitations - amount / acre / season pre-harvest intervals crops that can be grown in treated area next year

Bacterial Spot This disease is not common in Wisconsin, but a few incidents of it’s appearance are reported every year. Circular water-soaked spots up to 1/8 inch in diameter occur on the leaflets, eventually turn brown.

Bacterial Spot Xanthomonas campestris pv. vesicatoria infection on fruit begins with small, blister-like spots. As spots enlarge up to 1/8 inch in diameter, they assume a scab-like appearance.

Bacterial Speck Leaf lesions are small, round, dark brown to black dots and with time, display a halo. This bacterial disease is caused by Pseudomonas syringae pv. tomato.

Bacterial Speck On the fruit the lesions are very tiny and dark. The pathogen is seed-borne but can be spread from plant to plant by splashing rain or implements and machinery.

Tomato Diseases - Bacterial Spot and Speck Key Points Pathogens: Bacterial speck: Pseudomonas syringae pv. tomato Bacterial spot: Xanthomonas campestris pv. vesicatoria Favored by high humidity, rainfall/irrigation Pathogens seed borne Dispersal - wind driven rain, clipping plants, equipment moving between wet plants Optimum temperature: Bacterial speck: 65-75° F Bacterial Spot: 75-85° F

Tomato Diseases - Bacterial Spot and Speck Control Strategies Clean transplants, pathogen-free seed Plant rotation - at least 1-2 years between solanaceous crops Thoroughly incorporate plant debris after harvest Application of bactericides Fixed coppers - alone or in combination with fungicides Heavy rain, wind-driven rain, hail decrease efficacy

Buckeye Rot This rot usually occurs when the tomato fruit is in contact with the soil since the fungal pathogen, Phytophthora parasitica, is a soil inhabitant. Typical symptoms include concentric rings of light and dark brown tissue. Decay follows. Do not plant tomatoes in poorly drained soils. Mulch well around the base of the plants to protect the fruit from contact with the soil.

Soil Rot Alternating light and dark brown colored concentric rings characterize this disease. The soil fungus Rhizoctonia infects the fruit as it lies on the soil. As the fungus advances into the fruit, it causes a decay along with other secondary organisms. Mulch well around the plant to prevent fruit contact with the soil.

Tomato Diseases - Soil Rot of Fruit Key Points Pathogen: Rhizoctonia solani Symptoms: Rotted tissue showing concentric bands of alternating dark and light brown Initially, rotted area is firm but becomes mushy with invasion of soft rotting organisms Affected areas eventually turn black Overwinters in soil Fungus enters tomato where fruit contacts soil Symptoms may not be evident at harvest but can develop in storage or shipment

Tomato Diseases - Soil Rot of Fruit Control Strategies mulching around base of plants to avoid fruit contact with soil helps prevent infection mulches include straw, grass clippings, paper, plastic staking or caging of plants helps to avoid fruit contact with soil

Tobacco Mosaic Virus Contrasting light and dark green areas in a mosaic pattern are symptoms of this viral disease. Fruit symptoms are generally lacking, but yield reduction both in size and number may occur. Resistant cultivars are available.

Tomato Diseases – Tobacco Mosaic Virus (TMV) - Key Points: Pathogen: Tobacco Mosaic Virus Symptoms: Light and dark green mottled areas on leaves Necrosis of fruit with some strains Stunting of plants depending on growth stage at infection Virus easily transmitted by workers, machinery TMV may be present in tobacco products Virus survives on equipment, in plant debris

Tomato Diseases – Tobacco Mosaic Virus (TMV) - Control Strategies: Crop rotation – minimum of 3 years Workers should wash hands in detergent before handling plants Sanitize pruning equipment periodically Use cultivars with TMV resistance

Cucumber Mosaic Virus The mosaic pattern is similar to that caused by tobacco mosaic virus. With more severe infection stunting occurs and the leaflets take on a “shoestring” appearance. Severe infection causes a serious decrease in fruit production. Fruit that are produced are small in size and maturity is delayed.

Tomato Diseases – Cucumber Mosaic Virus (CMV) - Key Points: Pathogen: Cucumber Mosaic Virus Symptoms - foliar: Mosaic or mottle similar to symptoms produced by TMV “Shoestring” appearance of leaves (filiform or threadlike) General stunting of the plant Symptoms – fruit: Yield reduction – amount and size of fruit Fruit often misshapen Delay in maturity Numerous strains of the virus exist – many are specific to tomato Over 700 plant species are host to this virus Usually spread by aphids

Tomato Diseases – Cucumber Mosaic Virus (CMV) - Control Strategies: Eliminate weed hosts – such as Milkweed Chickweed Ragweed Clover White cockle Carpet weed Plant a non-host barrier (such as corn) around the tomato crop

Double Streak Virus When tobacco mosaic virus and potato virus X infect a tomato plant at the same time the disorder is called “Double Streak Virus”. Stem symptoms include necrotic streaks of various lengths and widths. Leaflets collapse and wilt.

Double Streak Virus Fruit symptoms of Double Streak consist of light brown spots. Sanitation is the most important means of preventing this disease. Workers who smoke should be directed to wash their hands well with soap and water. Any symptomatic plants should be removed and destroyed.

Blossom End Rot This is a physiological problem rather than a pathogenic one. A calcium deficiency in the blossom end of the fruit is responsible for this problem. Externally, tissue at the blossom end of the fruit collapse and turn black, usually giving the fruit a flattened black bottom. Affected tissues may be invaded by secondary fungi and bacterial leading to a soft rot of the fruit. Calcium deficiency in the fruit does not necessarily mean that the soil is deficient. Fluctuations in available water can cause this disorder. Mulch around the base of plants in order to keep the moisture supply constant. Irrigate when necessary.

Catface This problem can be caused by a number of factors. Frost or cold temperatures at the time of pollination resulting in partial fertilization is one of them. High nitrogen or extensive pruning or exposure to herbicides have also been implicated.

Growth Cracks Pictured here is “radial” cracking. Some cultivars are more susceptible to this phenomenon than others. It relates to the strength and stretch capacity of the skin (epidermis) of the fruit. Moisture amount and temperature fluctuations influence cracking. The cracks can be colonized by secondary rotting organisms. Less cracking occurs if the fruit is shaded from the hot sun by adequate foliage. Resistant cultivars are available.

2,4-D Injury The herbicide 2,4-D used in the area can be carried in on wind currents and cause distortion. This herbicide has growth regulating properties and can cause excessive cellular growth, twisting and distortion. Be mindful that spray drift can originate from as far away as several miles. Symptoms can be confused with those caused by virus infection.

Juglone Toxicity Walnut and butternut trees produce a toxin called juglone. Tomato plants are among plant species that are particularly susceptible. All the parts of the tree contain the toxin and when the roots of the tomato plant come in contact with the roots, stems, leaves, or nuts of the walnut tree, the toxin is taken up by the tomato and wilting results. Plant well away from the dripline of the walnut or butternut tree. Even if the tree has been cut down, the remaining roots continue to contain the toxin. The tomato plants in this slide are between the corn and beans. Note the trunks of the walnut trees in the upper center of the slide.

Juglone Toxicity This tomato plant is one from the row of plants from the previous slide. Wilting is apparent. Other symptoms can include growth stunting, yellowing and discoloration of vascular tissues similar to the Verticillium and Fusarium wilts described earlier.