Red thread is a cool-season turfgrass disease caused by the fungal pathogen Laetisaria fuciformis. Red thread is a foliar disease that usually occurs on taller mown lawns that are under stress due to low fertility, soil compaction and/or low temperatures. Cool (40-70 F), drizzly days and mornings with heavy dew are ideal for disease development. The pathogen spreads from plant to plant by growth on the fungal threads and by wind and human activities (mowing, weeding, playing). The pathogen survives the winter as specialized structures called sclerotia.
Symptoms: Red thread affects the leaves of Kentucky bluegrass, perennial ryegrass and tall fescue. Although the appearance of the grass is undesirable, the disease does not kill the plants. From a distance, disease symptoms appear as tan or pink-colored circular patches. Upon closer examination, tufts of pink threads can be seen on the tips of the grass blades.
Management: Red thread disease is mostly cosmetic, so fungicides are not recommended for residential lawns. The most important nonchemical management strategy is to implement an adequate nitrogen fertility program and promote healthy turf growth through soil compaction and water management. For non-residential turfs or high-value properties, a fungicide spray program can be implemented. Spray programs should begin prior to the formation of fungal overwintering structures (sclerotia). Information on the use of fungicides to manage red thread disease can be found in in the LSU AgCenter Disease Management Guide.
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The LSU AgCenter and the LSU College of Agriculture