Red Thread caused by the fungus Laetisaria fuciformis, is favored by cool, humid weather. Red Thread may become more common on lawns with fescue and ryegrass blends. Red Thread causes the lawn to have a bleached patchy appearance. Irregular areas, from several inches to several feet across, develop a whitish to pinkish color. Leaf blades and sheaths are attacked; at first they develop water-soaked or greasy green areas, then the affected parts dry out and become tan-colored. In wet weather the affected leaves are covered with a gelatinous pink fungus which then forms bright red threadlike strands near the tips of the leaves and from leaf to leaf.
The best temperatures for Red Thread development are 68-75 F. Red Thread can be quite severe on red fescue (a component of many shade-tolerant lawn grass mixtures) and may occasionally be severe on bluegrass.
Control with fungicides is not usually required for Red Thread. If soil nitrogen levels are low, fertilizing the lawn may help it to recover more rapidly. Deep watering and avoiding frequent light waterings, especially in late afternoon, may help to reduce damage. Collect grass clippings when the disease is active.