Symptoms and Signs
Anthracnose of tomatoes is primarily a disease of ripe and overripe fruit. Depressed, circular lesions about 0.5 inch (1.2 cm) in diameter appear on ripe fruit. With age the lesions become tan and dotted with small black specks (microsclerotia). Dark, needle-like spines, called setae, surround the microsclerotia and acervuli, cushion-shaped fruiting bodies that erupt through the plant tissue. During moist weather, masses of salmon-colored sausage-shaped spores may form on the lesion surface.
Infection may also occur on stems, leaves, and roots. Root infections (called black dot root rot) become evident when fruit begin to ripen. Root lesions are brown and dotted with microsclerotia. The cortex of infected roots is often completely rotted.
Comments on the Disease
The fungus is a weak parasite and generally infects ripe or overripe fruit and roots of mature plants. In California, anthracnose on fruit occurs infrequently because of its dry weather. Root rot, however, is not uncommon, especially where tomatoes are grown year after year in the same soils. The effect of black dot root rot on yields is not known.
Rotate with nonsolanaceous crops at least every other year. Avoid sprinkler irrigation when fruit begin to ripen. Fungicides are generally not required. Fungicides for black mold are effective against anthracnose fruit rot.