In frog-eyes an apparently healthy green patch of grass is partially or completely surrounded by a ring of dead grass. Distinct streaks, crescents, and circular patterns are found in the affected lawn area. Leaf lesions are often, but not always, associated with these diseases. If present, they are variable in size, shape, and color. Many other fungal diseases can also cause leaf lesions.
Microscopic examination is often necessary to determine the cause of the problem.
The fungus, Leptosphaeria korrae , survives unfavorable conditions as dormant mycelium or sclerotia in infected plants and plant debris. The fungus infects plants and produces symptoms in early spring. Symptoms fade as the fungus become dormant as summer heat increases but the reappear, as the fungus becomes active again in early autumn. The pathogen may be spread through infected turf and mechanical equipment. The primary stresses that influence disease development include excesses of thatch, fertilizer, and turf canopy temperature, as well as incorrect timing of fertilizer applications, low mowing height and low soil pH. Each of these stresses can be reduced through appropriate culture as described below.