Plant Disease Clinic -- Highlights

Red Thread - Turf

Red thread on turf was diagnosed in the Plant Disease Clinic last week. The disease is caused by the fungus Laetisaria fuciformis and primarily affects perennial ryegrass, red fescue, and Kentucky bluegrass. The name of this disease describes the primary symptom very well. Red, thread-like structures (fungal mycelium) are visible on the tips of grass blades or leaf sheaths. The structures are described as "antlerlike" appendages.

Red thread occurs during periods of cool, wet weather and is associated with periods of slow growth. Diseased areas appear blighted and range from a few inches to several feet in diameter. Grass blades at first appear water soaked. The tissue eventually collapses and turns a tan color. Red thread does not progress into crown or root rot stages, and seldom kills plants.

Since slow growing and poorly nourished turfs are most severely attacked, applications of nitrogen are helpful, but excessive rates should be avoided. Selective pruning of trees and shrubs to increase light penetration and air circulation is recommended. Collecting grass clippings when the disease is active may reduce the number of red threads that fall back into the turf. Where red thread has been a severe problem, labeled fungicides may be applied at 10-14 day intervals during prolonged, moist weather.

This article originally appeared in the July 21, 1993 issue, p. 122.

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