Pythium disease, also known as "Pythium blight," "cottony blight," or "grease spot," is a highly destructive turfgrass disease caused by several different Pythium species. All naturally cultivated cool-season turfgrasses are susceptible to Pythium and if conditions are favorable to Pythium it can destroy a whole turfgrass stand in a few days or less. Pythium favors hot and very humid weather and will usually develop in low areas or swales in the turfgrass. Symptoms Pythium symptoms will first appear as small, irregularly shaped spots that are 1/2" to 4" inches in diameter and will join together to form large patches that will often be long streaks. Pythium often develops into these streaks because it is the direction of water movement (drainage) most often ruts from golf carts and mowing equipment. The turfgrass leaves will at first look and feel water-soaked, greasy, or slimy. Once dew or moisture dries up the blade will shrivel up and collapse, often causing a matted brown turf. The turfgrass will begin to develop patches that fade to a light brown or gray color. With high humidity in early morning or throughout the day, diseased leaves may be covered with the white, cobwebby, mold like growth of the causal fungus, known as mycelium. Disease cycle Pythium may survive in the soil for extended periods of time, often coming from debris from past infected plants or spores living in the soil. Pythium spreads by the movement and growth of mycelium and spores from plant to plant. Pythium thrives in hot and humid weather typically day temperatures of 80°F to 95°F in areas that have little air movement but high moisture content. In lower temperatures of 55°F to 65°F and extended periods of wet weather Pythium is still prevalent. Pythium will most commonly appear during the "150 rule", which is when day + night temperatures are over . Pythium is most common when dew remains on the grass blade for 14 hours or more. Turf stands that have excess nitrogen and lush growth are very vulnerable to Pythiuum and will spread rapidly due to high nitrogen levels. Alkaline soils (above a pH of 7) and calcium deficient soils also tend to favor Pythium. Pythium survives over winter as oospores found in the soil. The pathogen therefore is easily spread with the movement of diseased plants, soil movement, surface water, or even from shoes. Pythium also causes "Damping off", "seed