The key components to outbreaks of red thread, caused by the fungus Laetisaria fuciformis, are cool moist conditions couples with slow grass growth. It is especially damaging to turf whose growth has been slowed because of low temperatures or low fertility. Red thread has become a serious problem on golf greens and fairways with the recent trend toward lower nitrogen rates on bentgrass. The application of growth regulators that retard plant growth also may increase the incidence of red thread. Weakened turf will continue to decline until corrective measures are taken to control the disease.
Drizzly days with temperatures between 65° to 75°F are most conducive to the development of red thread. Disease activity ceases during hot, dry weather but may resume in the fall. L. fuciformis survives the summer and winter as sclerotia and dormant mycelium in infected host tissue. The disease is spread by equipment contaminated with the casual fungus. Mowing turf in early morning when it is wet with dew contributes to the spread. Fungal structures also can be spread by wind or carried by running water. Individual diseased patches enlarge as the pathogen grows from leaf to leaf. When moisture droplets collect on the leaves, the fungal mycelium penetrates and cut leaf tips. Leaf death can occur within two days after infection.
Symptom patterns are circular to irregular patches with a pinkish to tan cast. The presence of uninfected leaves gives the patch a scorched or ragged appearance, and from a distance the turf may appear to be suffering from drought. Infected leaves die from the tip downward, but infection is confined to leaves and leaf sheaths.
During wet weather, affected leaves may become covered with pink gelatinous flocks of mycelium that sometimes bind the leaves together. When wet the patches not only appear pink but feel slimy to the touch. Pink to coral, threadlike fungal structures (sclerotia) protrude from the tips of infected leaves as branched, antlerlike appendages (red threads). The presence of these appendages distinguishes red thread from pink patch. They can be seen without the aid of magnification.
Maintaining an adequate and balanced fertility program can help prevent severe infection. When the disease is active, collect grass clippings. On turf with a history of red thread, start a preventive fungicide program when day temperatures are 60° to 70°F. Treatments should be repeated every 10 to 14 days as long as wet weather persists. For a curative program treat the turf every 4 to 5 days until it recovers.
J. E. Watkins. (1997). Diseases of Cool Season Turfgrass. In F. Baxendale, Ph.D., & R. Gaussoin, Ph.D., Integrated Turfgrass Management for the Northern Great Plains (pp. 122 – 123). Location: Nebraska
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