All turfgrass species
Pythium blight infestations start out as small, circular spots of
dead grass that run together as the infection spreads. When it is
hot and conditions are favorable, this disease can spread rapidly
in a 24-hour period. Infected leaf blades blacken and rapidly wither
and later turn reddish-brown. Leaves lie flat, stick together, and
appear greasy. Masses of white, cottony mycelia may appear. Pythium
blight occurs in parts of the lawn where it is wet and often runs
with the pattern of water drainage.
Conditions favoring disease
Pythium blight tends to develop in low spots that remain wet. Temperatures
between 80° and 90°F favor disease development. High nitrogen
levels also contribute to the disease.
Prevention and management
The key to preventing and managing Pythium blight is proper irrigation.
Avoid overwatering and improve soil aeration and
drainage. Do not mow when the leaf blades are wet and avoid applying excess
nitrogen during hot, humid weather. Reduce shading. Fungicides
are available but are usually not warranted in home lawns.
For more information on lawn diseases, refer to:
Pest Notes: Lawn Diseases:
Prevention and Management