Pinkish or reddish patches typically 3 to 15 inches in diameter. In the presence of rain or dew, the fungal growth is visible in the morning and red or pink mycelium may be present. As the grass dries, the red to pale pink hairs or strands, called tendrils, can be seen extending from grass blades. Red thread kills only the leaves of the plant, so grass will recover under less favorable conditions, such as summertime temperatures.
Susceptible species: Fine leaf fescues, perennial ryegrass, Kentucky bluegrass, and bentgrasses.
Favorable conditions: Red thread typically appears as grass comes out of dormancy in the spring, preferring wet weather and springtime temperatures (60 to 70 degrees F). It can also occur during periods of prolonged overcast and wet weather in the summer and in areas with mild winters.
Fungicides are available for control of red thread but are usually not necessary if proper cultural practices are implemented.
Photo credit: John Kaminski, Penn State