Cottony mycelium on turf located where water drains is likely due to an infection by which pathogen?

The presence of cottony mycelium on turf, particularly in areas where water drains, is indicative of an infection by Pythium blight. This pathogen, Pythium aphanidermatum, thrives in warm, moist conditions and is commonly associated with poorly drained areas of the lawn. The cottony appearance of the mycelium is a characteristic sign of Pythium infections, as the fungal growth tends to be fluffy and white, resembling cotton.

Pythium blight usually manifests when there is excess moisture, especially after irrigation or heavy rainfall, and is often found in low-lying areas where water collects. Understanding the environmental conditions that favor this pathogen is crucial for effective management and control. The identification of cottony mycelium specifically points to Pythium due to its unique growth habit, which differs from the other pathogens listed.