The stage that gives the infection its name is characterised by very thin, red, needle-like strands extending from the grass blade.
[1] The other stage is visible as small, pink, cotton wool-like mycelium, found where the blades meet.
Environment Laetisaria fuciformis, the fungus that causes red thread disease develops more often in cool (59–77 °F (15–25 °C)) and wet conditions.1 These conditions are more present in the spring and fall when rainfall is higher and temperatures are slightly lower.
Over 77 °F (25 °C), the growth rate of the fungus decreases significantly, and it ceases at 85 °F (29 °C).8 Turf grass that is poor in nutrition and are slow growing are areas that are more susceptible to red thread disease.2 The fungus grows from the thread like red webbing structures called sclerotia.1 The sclerotia can survive in leaf blades, thatch, and soil for months to years.
Having a balanced and adequate nitrogen fertilization program helps suppress the disease.3 A light application of quick release nitrogen reduces disease severity and is generally the only treatment necessary on residential lawns.8 This includes applying mild to substantial amounts of phosphorus and potassium to the turf.
Some of these turf grass species include annual bluegrass, creeping bentgrass, Kentucky bluegrass, perennial ryegrass, fine fescue, and bermudagrass.5 These species of grass are not the only types of turf that can be diagnosed with red thread disease but are the most common hosts.5 Noticeable symptoms of red thread disease are irregular yellow patches on the turf that are 2 to 24 inches in diameter.6 Affected areas are diagnosed with faintly pinkish web like sclerotia on the leaf blades.6 This sclerotia is the fungus growing on the leaf blades.6 This sclerotia has a reddish to pink spider web look to it.
[3] The infection will rarely kill the grass, usually only affecting the blades and not the roots, and the lawn should recover in time.