Red Thread

Predisposing Conditions for red thread

  • 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 of red thread  

Image of red thread on turf grass
Red thread on turf grass
  • 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. ¼ 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

Disease Cycle of red thread

  • 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

Type of Sample Needed for Diagnosis and Confirmation

The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if you plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states diagnostic laboratory for U.S. residents.  If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us

Management of red thread

  • 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

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