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Written by Laura H., Rutgers Master Gardener of Somerset County
When a long-lasting layer of snow cover occurs on cool-season turf during mid to late winter, gray snow mold may be noted as the snow melts. Leaf blades appear tan or white, hardened and matted into patches several inches to over a foot in diameter and covering much of the turf. It is caused by the fungus Typhula incarnata.
The infection cycle generally begins in late fall or winter during wet conditions and typically under the cover of snow, when soil is not frozen. The fungus spreads among grass blades, killing the leaf but not the root or crown. It thrives and causes the most damage in areas with a lengthy coverage of snow and with the greatest accumulation of snow, such as under piles and drifts, where the grass blades are dark and wet and where the temperatures are slightly above freezing. Newly seeded turf, low-mown turf, and areas amended with elevated levels of nitrogen are most at risk. During the spring melt, fungal activity diminishes and most grasses resume normal growth.
Management of gray snow mold includes cultural controls, such as ensuring that snow piles and drifts are lessened to the extent possible, continuing to mow lawns into late fall and easing up on the use of late-season nitrogen. Rake up damaged turf and reseed as needed. Dethatch as needed. Nitrogen can be applied to assist gray turf to return to a healthy state. Fine fescues and Kentucky bluegrass are less likely to become injured from this mold than other, cool-season grasses.
For expensive, highly maintained turfs, preventative combinations of fungicides can be used. They must be applied in late fall. Fungicides are not effective once snow mold has developed. It is important to read and follow pesticide label directions carefully for usage, storage and disposal.
Resources:
https://extension.psu.edu/turfgrass-diseases-gray-snow-mold-causal-fungus-typhula-incarnata
https://www.umass.edu/agriculture-food-environment/turf/fact-sheets/snow-molds