Pythium symptoms will first appear as small, irregularly shaped spots that are 1/2" to 4" inches in diameter and will join to form large patches that will often be long streaks.
[2] Pythium often develops into these streaks because it is the direction of water movement (drainage) most often ruts from golf carts and mowing equipment.
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.
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.
Creating an environment that includes adequate drainage, good air movement, and balanced fertility will help prevent the disease.
Improve air circulation (Installing fans, removing trees or shrubs) and avoid irrigation practices that will leave moisture on the grass blades for extended periods of time.
Most balanced fertility programs for Kentucky Bluegrass lawns will consist of applying 2–5 pounds (0.91–2.27 kg) of nitrogen per 1,000 square feet (93 m2) a year.
Timing is critical to prevent or stop the spread of Pythium, if continued hot, wet weather is expected, apply fungicides at the first sign of symptoms.