What pathogen causes cottony mycelium on turf where water drains?

Pythium blight is associated with the development of cottony mycelium in turf areas where water tends to drain or accumulate. This pathogen thrives in warm, moist conditions, which is often the environment created in areas that retain excess water, making turf susceptible to its effects. The mycelium appears as white to grayish fluffy growth on the grass blades and can quickly spread under ideal conditions of moisture and temperature.

Fusarium typically affects plants in a different manner, often leading to vascular wilt symptoms rather than the cottony appearance associated with Pythium. Rhizoctonia, known for causing brown patch, also does not produce the same type of mycelial growth and thrives in different conditions. Botrytis, while capable of affecting a variety of plants, typically presents in different forms and is not a primary pathogen of turf areas. Understanding the specific conditions and characteristics associated with each of these pathogens helps clarify why Pythium blight is the correct answer regarding cottony mycelium on turf.