Pythium blight

Pythium Blight

Pythium blight first appears as small reddish brown spots of blighted grass. Especially in the early morning, these spots may appear slimy and dark. Morning dew will also often highlight the mycelium growth where it occurs. Over time, the grass in these infected areas will shrivel and fade. The disease will often follow drainage patterns. The symptoms of pythium blight can be easily mistaken for those of leaf spot.  

Susceptible species & Favorable conditions

Susceptible species: All cool season grasses and Bermuda grass. Bentgrass, annual bluegrass, tall fescue, and perennial ryegrass have greater susceptibility.

Favorable conditions: Pythium blight can become quickly established during hot (80°-95°F), very humid weather. It can sometimes also occur at lower temperatures during cool, wet weather. It is one of the worst turf diseases, and can kill a plant in 24 hours in ideal conditions.

Recommended cultural practices

  • Avoid overwatering, and don’t water late in the day during periods of hot and humid weather. 
  • Ensure adequate drainage. 
  • Avoid mowing wet lawns. 
  • Avoid excessive rates of nitrogen fertilization to prevent lush growth, which is very susceptible to Pythium blight.
  • Aerate to reduce thatch levels and relieve soil compaction. 
  • Mow high

Chemical control: Multiple applications of fungicides as part of a preventative treatment program may be warranted to avoid spread of pythium blight.  

Photo credit: Lee Miller, University of Missouri,