Snow Mold

Snow mold is apparent on many lawns through Ohio. The snow mold fungi are most severe under a protective blanket of snow. Now that the snow has melted symptoms are apparent. Circular bleached patches a few inches to a foot in diameter become obvious. These patches sometimes overlap and cause large irregular areas of browning.

Problems commonly occur in years with prolonged snow cover. Snow molds get an early start when a wet, deep snow falls on unfrozen ground, and especially on lush juvenile turfgrass. The winter and spring weather this season was favorable for snow mold fungi in many areas.

image1 Two different types of snow mold diseases may develop, pink snow mold and gray snow mold. When wet, the bleached patches of grass caused by the pink snow mold fungus may show a light pink fluffy growth, especially at the outer edge of the patch. Patches caused by the gray snow mold fungus tend to be covered by whitish gray strands of fungus that glue the grass blades together.


The gray snow mold fungus produces survival structures called sclerotia. They are about the size of a pinhead and tend to be an orange-brown color. The sclerotia are embedded in the leaf tissue. A hand lens or magnifying glass is helpful when looking for sclerotia. The pink snow mold fungus does not produce sclerotia.

If a snow mold problem appears on turf this spring, several cultural practices can help manage the disease. Injury usually can be repaired by lightly raking the affected areas to encourage new growth. An excessive layer of thatch (more than 1/2 inch) should be controlled because it provides an ideal place for the fungus to survive during the hot summer months. Also improve drainage if necessary, because areas that stay wet can provide favorable conditions for snow molds and a number of disease organisms.

To reduce snow mold damage in the future keep grass mowed until growth has stopped in the fall to avoid long lush turfgrass going into the winter. Avoid excessive fall fertilizer applications. Snow fences can be used to prevent drifting in key lawn areas. Fungicides labeled for snow molds sometimes are applied on high-value areas and on areas where snow mold is a problem year after year.

As a compliment to this posting, a Microdochium patch turf podcast is available.
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Authors: Joseph Rimelspach