Hot, humid weather with occasional showers is favorable for cottony blight, caused by various Pythium species. This disease, also known as Pythium blight, can be very destructive in swards of creeping bentgrass and perennial ryegrass in a high-maintenance setting, such as golf courses, croquet courts, etc. Cottony blight can occasionally be found on other cool-season turfgrasses, though very infrequently.