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Management Updates: May 16, 2019

Red Thread
May 16, 2019

Red thread is caused by the fungus Laetisaria fuciformis. This fungus overwinters in soil and becomes active in spring. Its spores are dispersed by wind, splashing water, and human activity. The fungus penetrates grass blades through stomata and through wounds.

Red thread occurs in the cooler (60-75° F), wet weather of spring and fall. It is often seen in the spring before grass growth really takes off. The fungus produces reddish structures on the tips of infected grass blades, and dark pink patches appear in lawns. Red thread is largely a cosmetic issue. Patches eventually become pale and bleached out, and turf can take on a ragged appearance. It will not kill turf crowns or roots, but chronic, severe cases may eventually weaken turf. All turfgrass species are susceptible, though in general perennial ryegrass and fescues are more severely affected. Cultivars vary in susceptibility; resistant cultivars are available. Red thread is exacerbated by low nitrogen fertility, low soil calcium, water stress, and any other condition that slows turf growth.

If you’re a plant pathologist like me, you might think red thread is rather beautiful; turf managers and homeowners, however, may not agree with me. Fortunately for these non-believers, red thread is relatively easy to manage. Fungal growth slows significantly when the temperature exceeds 75°F, so the disease will disappear when summer heat arrives. Application of 0.2 lbs/1000 ft2 of quick release nitrogen in mid to late spring will help the turf recover. Have a soil test done and ensure that there is adequate calcium, potassium, and phosphorus available. Maintain a soil pH of 6.0-7.0. Ensure that mower blades are sharp to minimize wounding of grass blades. Collection and removal of clippings may be warranted with severe infestations. Manage thatch, which serves as a nice place for pathogens to hide out. Overseed with resistant cultivars.

Active red thread on lawn turf (J. Lanier)








Submitted by: Dr. Angela Madeiras