Anthracnose of Tomato
The fungus, Colletotrichum phomoides
Anthracnose is a common and widespread rot of ripe or overripe tomato fruit. Symptoms are rare on green fruit. Symptoms on ripe fruit are small, sunken, circular spots that may increase in size up to 1/2 inch in diameter. The center of older spots later become blackish. Spots may become numerous in severe cases and secondary rotting organisms may invade anthracnose lesions to completely rot infected fruit. The fungus forms small, dark survival structures called sclerotia in the centers of fruit spots. These sclerotia survive in soil for up to three years and cause infections either directly or by producing secondary spores. Green fruit are infected but do not show symptoms until ripening. The fungus then spreads from infected to healthy fruit as spores are splashed by rain or overhead irrigation, or by pickers working wet plants. Anthracnose is favored by warm rainy weather, overhead irrigation, and heavy defoliation caused by early blight.
Harvest fruit as soon as possible after ripening. Avoid excessive overhead irrigation or use drip irrigation to reduce moisture levels on fruit and humidity in the plant canopy. Fungicide sprays used to control leaf diseases reduce losses from anthracnose when applied on a regular schedule and in a manner to achieve thorough fruit coverage. A three-year rotation may also reduce chances for infection. Please contact your local county extension office for current information.