Infection may spread through root contact from plant to plant within the row, resulting in 6-12 infected plants in a row. The basal canker is light brown at first, then becomes bleached to white. The tissues in the canker develop a soft rot and eventually only the vascular bundles are left. Many sclerotia form inside the stalk. Infections of Sclerotinia wilt occur any time that sunflower is planted in a field that is infested with sclerotia.
Infection can occur at almost any soil moisture capable of supporting growth of sunflower.
Thus, Sclerotinia wilt is independent of environmental conditions and crop rotation is of utmost concern. By contrast, Sclerotinia head rot as well as Sclerotinia infections in canola, dry beans and soybeans develop from airborne spores. These infections need a wet soil surface for the sclerotia to germinate and form the mushroom-like bodies that liberate the spores. Continued wet weather is required for the spores to infect dead flower parts of susceptible crops. Thus, Sclerotinia head rot and Sclerotinia on other susceptible crops is highly dependent on wet environmental conditions before and at flowering.