Principle snow molds of the central and northern Plains are Microdochium patch (pink snow mold) and Typhula blight (gray snow mold). Other snow molds, such as sclerotinia patch, also may occur in certain areas.
Microdochium patch, caused by Microdochium nivale, can injure turf any time from mid-October to April during prolonged cool, wet weather. Infection most often occurs with temperatures between 32°F and 50°F during cold fogs, or in light drizzle. Conditions that bring on severe damage are heavy, wet snows occurring on unfrozen turf. High nitrogen fertilization in early fall or heavy top dressing will also enhance pink snow mold development.
Symptoms of pink snow mold on bentgrass greens or tees are roughly circular, rusty brown patches that range from 6 inches to several feet in diameter. On Kentucky bluegrass, fine-leaved fescues, and ryegrasses symptoms are more or less circular spots, mostly in the 4- to 12-inch diameter range. Within these spots, the grass is bleached and matted. When wet, a white to salmon-pink moldy growth is visible at the edges of the patches. The scattered spots are easily detected, even in midwinter, because of the contrast in color between the diseased spots and dormant turf. Unlike Microdochium patch, Typhula blight (gray snow mold) is strictly a cold-weather disease. Typhula blight, caused by Typhula ishikariensis or T. incarnata, can seriously injure turf during periods of extended snow cover.
The Typhala blight fungi spend the warmer months as sclerotia embedded in infected grass blades and in thatch. Snow cover and near freezing temperatures trigger germination of sclerotia and infection of grass plants. Early winter snows that are wet and cover the ground for several weeks initiate gray snow mold activity. Turf injury is aggravated when the snow is compacted by walking, skiing, snowmobiling, or sledding.
Symptoms of gray snow mold are most likely to develop where snow has drifted or been piled and is slow to melt. Patches of rough, dead, bleached-tan areas up to a foot in diameter become visible as melting snow recedes from diseased areas. When wet, they are often covered by a whitish-gray moldy growth. Typhula develops tiny orange to black sclerotia embedded in infected leaves. They are visible with a hand lens, and a magnifying glass can be used to distinguish between two snow molds.
Snow mold injury can be prevented through management and fungicide application. Dormant fall fertilization with a slow-release nitrogen carrier and mowing until leaf growth has stopped will prevent lush growth going into winter. Use snow fences to prevent drifting on high-value turf and to restrict traffic on frosted or snow-covered turf. Snow mold injury can be repaired by raking the affected turf in early spring and by lightly fertilizing to encourage new growth. Use a preventive fungicide program on high-value turf and on areas where snow mold cause injury year after year. Make the initial application in early to mid-November and repeat applications during midwinter thaws, as needed.
J. Watkins. (1997). Diseases of Cool Season Turfgrass. In F. Baxendale, Ph.D., & R. Gaussoin, Ph.D., Integrated Turfgrass Management for the Northern Great Plains (pp. 139-142). Location: Nebraska