RED THREAD FUNGUS ON TURF GRASS: Laetisaria fuciformis
Red thread occurs in the spring and fall during humid periods when the air temperatures are between 16°C and 24°C (60°F and 75°F). Fine-leaved fescues and some ryegrasses are particularly susceptible.
The first noticeable symptoms are water-soaked patches of grass in the spring. Infected grass blades soon die and fade to a bleach-tan color when dry. Infected leaf blades are often interspersed with healthy unaffected leaf blades giving the grass a ragged appearance. In severe cases, most leaf blades may be killed and diseased grass looks scorched or yellowed in irregularly-shaped or circular patches from 5 to 50 cm in diameter. The patches may be widely scattered or, if close together, may coalesce into larger spots.

In humid weather, the fungus Laetisaria fuciformis grows visibly on the infected grass blades and leaf sheaths. The fungus produces thread-like strands or web-like areas of coral-pink to blood-red hyphae on the tips of brown grass blades (Fig. 2). The strands can protrude up to 2 cm upward from the blade tips and are easily seen, hence the name "red thread disease".
The primary means of dispersal is the spread of infected tissue and bits of the "red thread” (sclerotia) to healthy areas of grass. Invasion by the fungus is quick, and leaves may begin to die 2 days after becoming infected. During dry conditions, the "threads" may be viable for up to 2 years.
Maintain adequate soil fertility. Where red thread has been a problem in the past, maintain a soil pH of 6.5 to 7.0. Avoid overwatering. Do not water the lawn in the late afternoon or evening. Provide good soil drainage. Do not allow thatch levels to accumulate. Where disease is severe, fungicide applications may be necessary. If it does become troublesome, a spring or fall fungicide application may be used to manage this disease.
Master Lawns has a fungicide treatment available for this Fungus Disease.