Yes, there is a disease called Snow Mold that occurs mostly in Northern regions. It is caused by several different fungi and affects many turfgrasses. The symptoms are irregular to circular patches of water-soaked, yellowed, or bleached turf. They sometimes bear a whitish, gray, or pinkish cast. There are two types of snow molds, gray and pink, that become active under the snow cover.

The web-like mycelium of pink snow mold (Microdochium nivale) may initially look white and mature to a faint pink/salmon color. Gray snow mold (Typhula spp.) is white to gray in color. The mycelium of both types of fungi will disappear quickly as the grass dries. A useful identifying characteristic of gray snow mold is the presence of tiny brown/black mycelial masses (sclerotia) on the blades and in the leaf sheaths of infected plants. These survival structures vary in size and color, becoming smaller and darker as they dry. The pink snow mold fungus does not produce sclerotia.

The damage from snow mold fungi usually becomes apparent as the snow melts and exposes the grass in late winter. Snow mold symptoms consist of roughly circular patches (approximately three to 12 inches) of dead and matted grass blades. In severe cases, these patches join together and may not be recognizable as individual circles.

It is useful to determine whether the disease is pink or gray snow mold because gray snow mold rarely damages more than the blades of the grass. Lawns with gray snow mold can be expected to recover fairly quickly even when damage appears extensive. Pink snow mold, in contrast, may invade the crowns and roots causing more serious injury. It is not unusual for both types of snow mold to be found in the same area.

Snow mold fungi are active at temperatures just above freezing in moist conditions. These conditions occur most frequently under snow cover or anything else that covers the grass, such as fallen tree leaves. Gray snow mold usually only occurs after prolonged snow cover. Pink snow mold may be active in cool, wet conditions from late fall through early spring even in the absence of snow or other covers, a factor which greatly enhances its potential as a damaging disease.

Snow mold fungi remain inactive during the warm months when other disease fungi are most active. They survive in thatch and on plants as sclerotia (gray snow mold) or as mycelial threads (pink snow mold). In the fall, Typhula species sometimes produce small, white or pinkish, club-shaped spore-producing structures that may be seen among grass blades in lawns that have not been recently mowed. They grow from sclerotia that were produced in the previous winter for survival over the summer.

As cool, wet weather develops, the fungi begin to grow and infect grass plants. Like all living organisms, these fungi require moisture to survive. The cold, dry air of winter prevents active growth. The shelter of leaves, snow or any other cover on the grass maintains the necessary moisture for growth. Optimal conditions for snow mold activity occur when snow falls suddenly and remains on ground that has not yet frozen. In such cases, grass is often still lush, providing an excellent food base for the fungi.

Snow molds do not occur in the home lawn every year, but are most common during years when an early, deep snow cover prevents the ground from freezing. A cold, open winter will not promote snow mold, but may cause winter injury. The damage caused by snow molds is seldom serious. Generally, infected areas are just a little slower to green up.

If you take the following steps, you may be able to minimize damage in future years:
• Avoid excessive applications of nitrogen fertilizer in the fall.
• Continue to mow lawn at the recommended height until no longer actively growing.
• Rake up leaves in the fall.
• Manage the thatch layer to avoid accumulations of more than ½ inch.
• Spread out large snow piles to encourage rapid melting.

Chemical management is not recommended, especially if you have small children or animals that go outside. But if you must use a chemical, fungicides are most effective if applied just before the first lasting snow fall. Fungicides are not effective in spring after the damage has already occurred unless pink snow mold is involved. Pink snow mold may renew activity if cool, moist weather conditions prevail and may warrant treatment.