In field-grown tomatoes the fungus attacks the stem near the soil, and in greenhouse tomatoes it attacks the stem at a node that is often 1 m above the ground. The fungus causes a brownish decay of the soft tissues of the stem. Eventually, the plant wilts and dies. As the disease progresses, a grayish white fungal growth may cover the surface of infected tissues. At a late stage of the disease the infected portion of the stem, when broken open, shows cavities filled with white cottony fungus in which hard black sclerotia are embedded.
The fungus can survive as sclerotia in plant refuse in the soil for several years. Under favorable conditions the sclerotia germinate and produce cup-shaped bodies, 1-5 mm in diameter, which release spores. These spores are ejected into the air and can cause infection similar to gray mold at the nodes along the stem. The sclerotia only germinate when they are within about 3 cm of the soil surface; deeper ones remain dormant until they are brought to the surface by cultivation.
