With maturity, the center of the spot has a dark brown color. Infection occurs first on older foliage. High humidity and temperatures between 60 to 80 degrees F favor disease development. Varieties vary in their reaction to the fungus. The fungus causing this disease occurs in most fields but seldom does economic damage.
Infection requires high temperatures and presence of surface moisture.
The first symptom of the disease is small circular spots. As they mature they turn dark brown. Rotation and deep burial of stalks will help reduce losses to this fungus. Infected plants are chlorotic, stunted and have striped leaves. Infected leaves have a downy growth on the underside, toward the basal part.