University of Wisconsin - Extension

Because of the extreme cold this winter, you may see evidence of snow mold in your lawn. Snow mold is a collective term for winter diseases caused by cold-loving fungal species.

?The snow molds are unique because of their ability to attack grass plants at low temperatures,? said University of Wisconsin-Madison/Extension turfgrass pathology specialist Geunhwa Jung,

Most home lawns are Kentucky bluegrass turf, which usually escapes all but the most extreme winters, such as this past winter, with only superficial injury. Lawns should be raked in early spring to dry the surface and encourage renewed growth. Severely damaged turf will require plugging or overseeding to hasten its recovery.

High-value turf areas that are likely to be damaged by snow mold?such as golf course greens and tees?should be treated in late fall each year with appropriate fungicides. Late fall (dormant) fertilization enhances the recovery of damaged turf the following spring. Good surface drainage can sometimes also help reduce the severity of winter damage.

The most common snow mold fungi species in Wisconsin are Typhula and Microdochium, according to Jung. Typhula blight includes both gray and speckled snow molds. Typhula blight appears as matted turf at the edge of receding snow and is covered with cobweb-like fungal mycelial growth. Tiny black or brown fungal bodies called sclerotia are often found in the mycelium or embedded in the turf tissue.

?The symptoms of Typhula blight can be seen as snow starts to melt,? Jung said. ?It is most severe when heavy snow falls on turf that is not yet frozen and the turf, particularly unclipped, remains covered for a long period such as happened this past winter.?

Pink snow mold, or Fusarium patch, is caused by the fungus Microdochium nivale. It produces circular or irregular dark gray patches of turf (4 to 15 inches in diameter) and the affected grass becomes matted together during cold, wet periods. Pink snow mold is most common from October through April during cold, wet periods. Sometimes, affected turf develops a pinkish cast to it after the spring snow melt. Pink snow mold is more likely than Typhula blight to occur in association with cold rains and can cause serious damage when it occurs.

Gray snow mold is more common than pink snow mold, but the two can occur together and may be difficult to distinguish. Typhula blight is more common in the north, where it damages golf courses whether they have been sprayed with fungicides or not.

For more information about turfgrass diseases and lawn care, contact your County UW-Extension Office or visit the web site of the Urban Agriculture/Horticulture Team at http://www.uwex.edu/ces/wihort. Publications on lawn care are also available for viewing on the Cooperative Extension Publications web site at http://www1.uwex.edu/ces/pubs/index.cfm"> http://www1.uwex.edu/ces/pubs/index.cfm.