The sudden appearance of large, irregular or circular patches probably are not symptoms of Pythium blight, but more likely those of brown patch, summer patch or necrotic ring spot. Pythium blight may occur in streaks conforming to surface drainage patterns, in localized low spots where water puddles, or in larger areas where the individual spots have coalesced. The spots developing on higher cut lawns or fairway turfgrass tend to be larger and more irregular in shape than those occurring on golf greens and tees where the turf is cut short. White fungal mycelium that resembles a cotton ball. In the morning dew, infected grass leaves appear water-soaked, slimy to the touch, and dark green.
Infected plants collapse and cause the grass in the blighted spots to appear matted.
Sometimes the infected area may give off a fishy odor. This odor can be detected by removing a plug of diseased turf and placing it into a plastic bag. Seal the bag, and put it in a warm spot. Within a few hours both the fishy smell and characteristic mycelium should be noticeable. The disease is most easily diagnosed when the infected area is observed in the early morning when the characteristic mycelium and greasy appearance of the blighted turf are present.