The last couple of weeks I have been following the progress of Red Thread, a fungal disease of turfgrasses caused by Laetisaria fuciformis, on some research plots at the ISU Horticulture Research Station. The turf stand present is a mixture of perennial ryegrass and Kentucky bluegrass. The disease is named Red Thread because of the red threadlike structures that grow from the infected leaf tissue and are visible in the early morning hours, and the diseased area looks brown or tan from a distance. The disease started as small spots and can grow together to form larger areas of blighted turf. Typically red thread will be present on turfgrass that is growing slowly (under fertilized, drought stress, and high temperature stress to name a few stresses). Red Thread has a wide range of temperatures it can be active in, but it does best around 70 degrees Fahrenheit. The last several nights the lows have been in the 70's, making this perfect red thread weather. Two cultural options to help with control of red thread are to fertilize to speed up growth, and check to make sure the irrigation is running closer to sunrise to minimize the hours the leaf tissue is wet. Many fungicides are available if chemical control is necessary as well, make sure to follow instructions on the chemical label.
Red Thread turfgras disease on Kentucky bluegrass and perennial ryegrass.
Red Thread is named for the red threadlike structures that come out of the top of the infected leaf blades.
Red Thread spots look brown or tan from a distance.