The fungus which causes red thread infects the grass blades and leaf sheaths of fine-Ieaved fescues (red and chewings), perennial ryegrass, Kentucky and annual bluegrasses, and bentgrass during warm, damp weather in the spring and autumn. Fine-leaved fescue and perennial ryegrass are very susceptible. Less susceptible grasses include bermudagrass, sheep fescue, tall fescue, hard fescue, and zoysiagrass.
Irregular to circular, ragged, light-tan to pinkish patches, usually 2 to 24 inches wide, develop during prolonged warm (65-75 F), very humid weather. The spots may merge to form large tan, "scorched" areas with a reddish brown cast. Field symptoms are often confused with dollar spot. A diagnostic feature for red thread is the gelatinous pink threads which protrude from the leaf tips and sheaths and later become dry, brittle, and dark red. Affected leaves are generally interspersed with unaffected leaves, giving the patch an overall diffuse, scorched, or ragged appearance.
This disease was formerly known as Corticum red thread, a name which may still be found in the older literature and on some fungicide labels. Most fungicides labeled for red thread also mention a disease called pink patch. Of the two diseases, red thread is more important and since the symptoms, biology and management of both diseases are sufficiently similar, only red thread is discussed here.
Red thread is an important disease, especially on slow growing, nitrogen-deficient turf during rainy or very humid weather in the spring and autumn. Other factors that favor disease development include excess thatch, low calcium levels in the soil, water stress, a sudden drop in temperature, misused herbicides, and attack by other pathogens. Although red thread rarely kills turfgrass plants outright, it does weaken them and contributes to their decline and death from subsequent stresses or diseases.
Maintain adequate fertility, especially nitrogen. Varieties of the major turfgrass species vary in susceptibility. Where necessary, fungicide applications applied at 7- to 21-day intervals during moist weather in the spring and autumn are effective.