Red Thread

Laetisaria fuciformis

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  • Red thread is caused by the fungus Laetisaria fuciformis. Fine-leaved fescues and perennial ryegrasses are very susceptible. Although red thread rarely kills turfgrass plants outright, it does weaken them and contributes to their decline and death from subsequent stress diseases. Red thread is favored by slow-growing, nitrogen-deficient turfgrass, excess thatch, low calcium levels in the soil, water stress, a sudden drop in temperature and misused herbicides. The fungus forms conspicuous, coral pink, orange or red mycelial masses on the grass blades and leaf sheaths. In moisture-saturated air, the gelatinous masses may completely cover the leaves and mat the blades and leaf sheaths together. Where infection is severe, diseased turf is bleached tan or yellowed in roughly circular- to irregular-shaped patches, varying from an inch to more than 1 foot in diameter. Spreading occurs by splashing or flowing water and by wind, shoes, mowers, and other turfgrass equipment. Infection and disease development are favored by air temperatures of 60 to 75° F coupled with prolonged periods of overcast weather, light rains, heavy dews, fog, and moisture-saturated air.


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