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

Control

  • 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.

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