Diseases Turfgrass Diseases Pythium blight, Pythium aphanidermatum Pythium blight, also known as grease spot and cottony blight, can be a highly destructive turfgrass disease, especially on bentgrasses and ryegrasses. Severe outbreaks can completely destroy the turfgrass within a few days if weather conditions favor disease development.
Leaves appear water-soaked in appearance at first, then shriveled.
Diseased patches fade to a light brown or gray color. Groups of spots frequently join together. At times, the shape of the affected areas may resemble elongated streaks. Both the presence and pattern of these streaks seem to be determined by the flow or presence of surface water. With high humidity in early morning or throughout the day, diseased leaves may be covered with the white, cobwebby, moldlike growth of the causal fungus.