Red thread on turf is one of my favorite disease. It is so easy to diagnose because of the pink to light reddish color on top of the grass. If you look closely, you will find reddish thread-like structures on the tips of infected blades. These are strands of mycelium that arises from infected leaf blades and sheaths.
The red thread fungus, Corticium fuciforme survives over the winter in diseased leaf tissues or debris as mycelium and as stroma. It becomes active during extended periods of cool, wet weather and in temperatures between 60 to 75 F. It is severe in slow growing turf due to low fertility and/or nutrient deficiency, or from drought stress. In affected areas, turf looks blighted and discolored and appears to have a roughly circular pattern. Some live shoots can emerge from infected areas. Wind, foot traffic, mower, and other equipment used in the lawn can move the fungus from one infection site to another. Usually red thread ceases when temperature rises and conditions favorable to good turf growth resumes. However, we recommend mowing the lawn at least once a week to remove infected leaf blades. Infrequent but deep watering will help specially during daytime to prevent drought stress as well as decrease leaf wetness.
Fungicide sprays registered for red thread include Daconil and Cleary's 3336. Kentucky bluegrass cultivars resistant to red thread are available in the market.
This article originally appeared in the July 10, 1998 issue, p. 91.