WSU Extension

Hortsense

Lawn and Turf : Microdochium patch (Pink snow mold)
(revision date: 6/22/2015)


Biology
Fusarium patch is a fungal disease common in western Washington. It is typically most severe on bentgrass and annual bluegrass at low mowing heights in shaded areas. Fescues, Kentucky bluegrass, and perennial ryegrasses may also be infected. The disease develops most rapidly during periods of cool, wet weather in spring and fall. Symptoms include small, watersoaked patches which may be 2" in diameter initially, then enlarge to 6" or more. Reddish-brown margins often surround the spots, which become tan or light gray. White to pinkish fungal growth may be present on the advancing edges. Patches may appear ring-like if grasses regrow in the center. Symptoms are most noticeable on short grasses (1/4") and less noticeable on longer grasses (1" or more). The fungus survives in the soil and on diseased grass and debris. In areas with snow cover, the fungus can grow beneath the snow as the snow melts.
Management Options

Non-Chemical Management
  • Provide adequate, balanced fertilization to help prevent disease. Avoid excessive nitrogen in late fall. Fertilizers with moderate levels of nitrogen (preferably ammonium sulfate) are best for fall use. Do not use urea in the fall.
  • Mow regularly until growth stops in the fall. Remove clippings.
  • Good air circulation and good drainage help prevent disease.
  • Remove thatch and aerify as needed.
  • For more information on proper care of lawns see EB0482E, Home Lawns.
Select non-chemical management options as your first choice!

Chemical Management

Not recommended for home lawns because grass often recovers when the weather changes.

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Caption: Fusarium patch
Photo by: R.S. Byther
Caption: Fusarium patch
Photo by: R.S. Byther