Lawn Diseases - Snow Mold
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 (at least 3 to 12 inches) of dead and matted grass blades. In severe cases, these patches coalesce and may not be recognizable as individual circles. Just after snow melt and while the grass remains moist, it may be possible to differentiate between the two common types of snow mold found in New England by their color. The web-like mycelium of pink snow mold (Microdochium nivale) may initially look white and mature to a faint pink to 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 to 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.
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. All common lawn grasses may be infected, but Kentucky bluegrass-fescue lawns are the least susceptible to severe damage.
Pink Snow Mold
Grey Snow Mold