Snow Mold is a disease that may affect all cool-season turfgrasses, but tends to be most damaging to creeping Bentgrass and annual Bluegrass. The fungus blights the grass leaves, but typically doesn’t affect the roots or crown. On lawns and professional landscapes Snow Mold is most prevalent on turf that is maintained at heights too high (3”+) for the time of year (late fall – early spring).
On short-mown turf, snow mold symptoms appear as well-defined circular patches. During cool, wet conditions, white-pink Mycelium may be seen on infected leaf blades. Patches of dead, matted leaf blades can also occur on taller-mown grass, but often lack the circular pattern. Gray snow mold requires snow cover for infection and patch development, but pink snow mold does not need snow cover for extensive infections. Matted turf and snow acting as an insulator, will extend the duration of the temperatures that are favorable for both types of snow mold disease development.
Pink snow mold favors wet conditions, and can develop in a broad temperature range (30-60 degrees F). The pink snow mold pathogen survives with infested leaf residue in the thatch and decaying turf debris. Growth of Mycelium from initial infection sites results in distinct round patches. The pathogen will produce abundant spores at the patch margins. Rain can dislodge the spores and disperse them along the drainage pattern, which will start new infections.
Gray snow mold favors wet conditions and develops in colder temperatures (32-36 degrees F). Gray snow pathogen activity occurs in the fall during periods of cool, wet weather. Extended periods of snow cover provide ideal conditions for establishment and spread of gray snow mold. Although matted grass blades may provide an insulating environment, outbreaks normally are not sever without prolonged snow cover.
The best method to control snow mold is proper cultural practices. Cut the lawn short in the late fall, and rake up any fallen leaves to prevent your turf from becoming matted down. Also lightly raking the lawn in the spring will allow air to circulate around grass blades, and recover as temperatures rise. Fungicide applications are not recommended for home lawns. Fungicides are expensive, and with correct cultural practices you will be able to prevent snow mold, in most cases, from becoming an issue.