The grass turns light tan to pink in areas 2 inches to 3 feet in diameter. Pink webs bind the grass blades together. As the blades dry, pink threads, 1/4 to 3/4 inch long, protrude from the diseased leaf tips. Red thread is most serious on fine fescue and ryegrass lawns, but bentgrass, bluegrass, and bermudagrass are also susceptible. Red thread is most active in cool, wet weather.
Lawns that are growing slowly because of a lack of nitrogen are most severely affected by red thread. Mildly diseased lawns may improve if the nitrogen content of the soil is increased. Red thread is seldom serious enough to kill the lawn.