Snow Mold
By Mary Small, M.S., Diagnostician
CSU Extension/Jefferson County Plant Diagnostic Clinic
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.