Red Thread on Turfgrass

Photos of red thread can be viewed at the Plant Disease Clinic website under "Plant Diseases".

Predisposing Conditions:

  • water-saturated environment associated with rainy weather
  • slow shoot growth caused by nitrogen deficiency or water stress (although the disease also may develop in well-fertilized turf)

Symptoms and Signs:

  • tufts of pink or reddish web-like fungal growth can be seen on leaves, sometimes binding leaves together
  • infected leaves may appear water-soaked
  • leaves eventually become blighted, appearing a bleached tan color
  • bright red fungal structures, called "red threads" (approx. 1/4 inch or less long), can be observed extending from leaf surfaces, particularly the cut ends of the grass blades
  • affected areas initially are 1-2 inches, but may coalesce and form irregular shapes
  • dead leaves often are interspersed with green leaves

Biology of the Disease

  • caused by Laetisaria fuciformis, a fungus
  • infection occurs on the leaf and stem parts, not the roots
  • rarely kills plants, but does weaken turfgrass, contributing to decline from other stresses
  • spread by water splash, wind, mowers, shoes, and other mechanical means
  • red threads, when dry, function as survival structures (sclerotia), allowing the fungus to survive from season to season


  • maintain adequate fertility
  • raise the mowing height, if possible
  • avoid mowing early in the morning when the turf is wet with dew
  • avoid frequent sprinkling in the late afternoon
  • collect grass clippings when red thread is active to reduce the number of red threads that fall back into the turf
  • a fungicide program may be necessary on turf with a history of red thread
  • labeled products include Banner, Cavalier, Chipco 26019, Cleary's 3336, Compass, Dithane, Fore, Heritage, Junction, Mancozeb, Pentathlon, Protect T/O, Rubigan, and others

This article originally appeared in the July 14, 2000 issue, p. 86.


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 14, 2000. The information contained within may not be the most current and accurate depending on when it is accessed.