Snow Mold

Problem type: Disease

Name of problem: Gray Snow Mold; Pink Snow Mold

Plant name(s): All cool season grasses, perennial ryegrass, annual bluegrass, bentgrass

Symptoms / Characteristics:
Symptoms of snow mold become evident as snow melts, showing distinct dead patches of grass in the spring. Patches are usually circular in shape and can measure from 2 inches to 2 feet in diameter. Under optimal conditions, the patches may coalesce to be much larger. The leaves in these areas appear water soaked, followed by a bleached appearance. The affected grass blades appear matted together and are often covered by a whitish-gray moldy growth, appearing like cobwebs. Pink snow mold may have a salmon-pink mold visible, bordering the patch. These fungal structures are most evident when wet in the early day.

Snow mold is a cold weather disease with gray snow mold requiring snow cover and pink snow mold requiring only cool, moist conditions. Snow mold fungi are always present in lawns, but only become active when conditions are moist and temperatures stay around 0°C. Cool springs, with a long period of snow melt favors disease development. Fungal bodies can be seen with a magnifying glass embedded in plant tissue as match-head size or smaller structures, appearing light brown early in the season and eventually turning darker in color. Disease severity is high when a wet snowfall occurs before the ground is frozen. Frequent light snowfalls followed by snow melt, maintain the cool, wet environment that favors disease development. Factors promoting development of snow mold include, high humidity, temperatures at or just above freezing, persistent wet drizzle or fog, thick thatch layer, alkaline soil (pH above 6.5) and poor drainage.

Control / Preventions:
Injury from snow mold is usually superficial, only killing the leaf blades, but in severe cases the entire plant may die and overseeding may be necessary. Avoid fertilizer applications with high nitrogen in the fall to avoid excessive shoot growth. This keeps grass tissue soft and succulent, making them more susceptible to attack from the fungus. If an application is made, be sure to use a slow release type.

Mowing grass late into the fall and raking up leaves will prevent tall grasses and debris from matting and creating a favorable environment. Reduce thatch by vertical mowing, aerating or power raking. On higher quality grasses, avoid snow compaction by reducing snowmobile, skiing and other traffic on the area. Prevent excess snow from accumulating in one area by the use of fences and shrubs. Snow may need to be physically removed in the spring to help speed up the snow melting process.

Damaged areas can be raked and debris removed to disrupt the matted grass in the spring. Normal fertilizer and water during the growing season is all that is needed to encourage growth of grass. If there are bare areas still evident by mid-summer, the area can be re-seeded. Chemical controls are available for snow mold control and should be applied in late fall before snow cover. Products include Daconil 2787, Rovral, Rovral Green and Quintozene. Chemicals are not always necessary and should only be used in areas with a history of snow mold damage. All chemical products should be handled carefully and labels read thoroughly for safe, effective applications.