Snow Mold

Symptoms: Damage from snow mold usually becomes apparent as the snow melts and exposes the grass in late winter. Snow mold symptoms consist of roughly circular patches of dead and matted grass blades. Just after the snow melts and while the grass remains moist, it may be possible to tell between the two common types of snow mold found in Northeast Ohio by their color. The web-like fungus of pink snow mold may initially look white and mature to a faint pink to salmon color. Gray snow mold is white to gray in color. 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 to black masses on the blades and in the leaf sheaths of infected plants. Pink snow mold does not produce black masses on the blades and in the leaf sheaths. 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, however, 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. All common lawn grasses may be infected, but Kentucky bluegrass and fescue lawns are the least susceptible to severe damage. Season: 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, which greatly enhances its potential as a damaging disease. Disease Cycle: Snow mold fungi remain inactive during the warm months when other disease fungi are most active. They survive in thatch and on plants. 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 source of food for the fungi. Cultural Management: The most important means of preventing or reducing snow mold problems in lawns is the care of the grass at the end of the fall season. As long as the grass continues to grow, it must be mowed. Fall fertilizer should be timed so that it will not influence additional growth to the grass. Fall fertilizers should be applied more than four weeks before dormancy. Because snow mold activity is greatest when covered with moist conditions, all leaves or other materials should be removed from the lawn. In addition, it is best to avoid piling snow deeply along sidewalks and driveways where it will form a long-lasting snow bank. Chemical Management: Fungicide applications for snow mold are not recommended. The cultural practices described above are the most effective means of reducing snow mold damage. In most cases, the grass will resume healthy growth in the spring, even though damage may appear widespread when the snow melts. It is important to lightly rake the affected areas up to allow airflow and photosynthesis to occur.

This particular area does not get much sun and the snow is more apt to hanging around longer between thaws.

Close up picture of “matted” grass from snow mold.