Pythium blight

Small (2–5 cm) greasy, water-soaked, dark patches that may streak along drainage or mower paths. Fluffy white "cottony" mycelium appears under high humidity.

The symptoms of Pythium blight can include small, dead spots on the turfgrass, which can enlarge and coalesce into patches or widespread blighting. The leaves may appear dark or water-soaked and have a greasy feeling between fingers.

White cotton-like mycelium is often present, especially after periods of high humidity. The pathogen also produces oospores (double-walled sexual spores) and zoospores (asexual spores with flagella-like structures). These spores can be spread by water movement, mowers, and traffic.

Pythium aphanidermatum is a fungus-like organism that causes Pythium blight in turfgrass. It is a facultative parasite which can infect a wide range of plant species and grow as a saprophyte in soil. It reproduces asexually by means of sporangia and zoospores, and can also reproduce sexually by means of oospores. The pathogen thrives in warm, moist conditions and can cause severe damage to turfgrass in these conditions. It is important to note that it is not a true fungus, but a member of the kingdom Chromista.

Pythium blight is most active during the summer months, from June to August, and is often associated with hot days (85-95F) and hot nights (>68F), as well as high humidity and prolonged leaf wetness. The disease may start as small, dead spots that enlarge and coalesce into patches or widespread blighting and may follow drainage patterns.