Pythium fungi can infest all commonly grown cool-season lawn grasses.
When Pythium attacks foliage, the disease is called cottony blight, grease spot, or Pythium blight. Outbreaks occur most often during hot, humid weather and can spread quickly. Pythium can also cause root and crown rots in cool, warm, or hot weather with high moisture.
Look for small patches up to 6 inches wide where the grass looks water-soaked and feels greasy or slimy. Patches often follow the direction of drainage or mowing.
To help prevent Pythium problems:
- Use low to moderate rates of balanced fertilizers. (High nitrogen favors the disease with some grasses.)
- Maintain soil pH in the neutral to slightly acid range.
- Avoid mowing when the grass is wet.
- Water early in the day so grass dries quickly.