The blades may twist and collapse at the lesion. Microscopic examination may allow for detection of oospores within the plant tissue. These circular spores can vary in diameter from 12 to 38 m but only those with oospores above 20 m in diameter are considered to be serious pathogens of turfgrass. This pathogen survives over winter and periods adverse to disease development as resistant oospores in the soil. It can be moved from one area to another by soil movement, by transporting diseased plants or plant parts, and by equipment, shoes, or surface water.
Diseased plants serve as infection centers from which the fungus spreads.
Spread from these areas can be rapid in wet or humid, hot weather. High nitrogen fertility favors the disease on many grass varieties. Alkaline soil and calcium deficient soil also tends to favor the disease. Maintain grass growth by low to moderate rates of balanced fertilizers, and maintain soil pH in the neutral to slightly acid range. Avoid mowing when the grass is wet.