Regular irrigation greatly reduces charcoal rot and is the single most important control measure. White mold, Sclerotinia sclerotiorum , is most severe during prolonged cool, wet weather in the spring or fall. The fungus is not host specific, so spores produced on one crop will easily infect others. The most obvious symptom of white mold is a white, cottony mycelium produced at the base of plants. Sunflowers infected with white mold wilt and die.
Sclerotinia also causes a head rot.
Black sclerotia, about the size of a small lumpy sunflower seed, may be found on the surface of stem cankers, on blighted heads, and inside the pith of stems. These sclerotia are the overwintering structures for the fungus and provide the infective spores for the next disease cycle. Southern blight, Sclerotium rolfsii , can be a troublesome disease during hot summers. The first symptoms are the wilt and death of plants following several weeks of hot weather. Upon close inspection, growers will find a white cottony mycelium on the base of the plant and small, round, tan sclerotia that resemble mustard seeds on blighted tissue and at the soil surface.