Snow mold is a fungal disease that develops when snow falls on unfrozen turf and remains there for long periods of time. The most severely damaged grass is found adjacent to driveways (where large piles of snow accumulate from shoveling) or where there are snow drifts. Snow mold fungi thrive in temperatures just above freezing, conveniently provided by the long-lasting snow cover!
As snow recedes, circular patches of light yellow, straw or brown-colored turf suddenly appear. The grass blades in these patches are matted and may be covered with gray or white webbing. As the grass dries out, webbing disappears and the patches crust over. Grass blades may be killed if infestations are severe. When temperatures warm, new leaves develop and the lawn begins to recover. Damaged grass may be a bit slower to green up.
Although infections begin in winter under snow, fungal growth may continue after snowmelt if the grass remains cool and wet. Once temperatures regularly exceed 45 degrees or the lawn dries out, gray snow mold activity stops.
To manage snow mold, rake the patches to break up the crust and dry out the lawn. You can follow this with a light fertilizer application in early spring. Fungicides are available, but must be applied in the fall.
Fortunately, snow mold infestations don’t happen every year. Environmental conditions must be just right for the disease to occur and piles of long-lasting snow aren’t that common in the Metro area.