Snow Mold on Grass: Causes and Treatments

Snow mold on grass is a fungal lawn disease that often appears when snow melts in early spring. This condition is caused by certain fungi, such as Microdochium nivale (pink snow mold) and Typhula spp. (gray snow mold), which thrive in cool, moist conditions under snow cover.

Causes of Snow Mold on Grass

After winter, snow mold manifests as discolored, matted patches of grass that can be gray, white, or pinkish. These patches are often accompanied by a fine layer of white fungus on grass, especially around the edges of affected areas. Left untreated, snow mold can harm the health of your lawn.

Causes of snow mold on grass include the following:

Excessive Snow Cover

One of the primary causes of snow mold on grass is prolonged snow cover. When snow falls before the ground has frozen, it traps heat and moisture, creating a breeding ground for fungal spores. Thick layers of snow or large snow piles exacerbate the problem, extending the damp conditions that fungi love.

Poor Lawn Maintenance

Poor lawn care in the fall is another significant contributor to snow mold. Failing to mow grass to an appropriate height or leaving debris like leaves and twigs on the lawn provides organic material that serves as a food source for fungi. Thick thatch can also trap moisture and reduce airflow.

Cool and Wet Conditions

Cool, wet weather in the fall and early spring can contribute to the development of snow mold on grass. These conditions allow fungal spores to activate and spread even before snow arrives. Extended periods of dampness are especially problematic for lawns that are already stressed or poorly maintained.

Recognizing Snow Mold on Grass

The signs of snow mold are often visible as the snow begins to melt:

• Discolored Patches: Look for irregular patches of grass that are gray, pink, or whitish in color. These areas may appear waterlogged or matted.
• White Fungus on Grass: A thin, web-like layer of fungal growth may form on the surface, particularly around the edges of the infected patches.
• Matted Grass Blades: The affected grass often clumps together and becomes flattened, making it difficult for healthy grass to regrow.

Pink snow mold tends to be more aggressive and can kill grass roots, while gray snow mold usually affects only the surface.

Treatments for Snow Mold on Grass

If you have white fungus on grass, there are treatments to help your lawn recover, including the following:

Rake and Aerate

Raking the affected areas is one of the simplest and most effective treatments for snow mold on grass. Raking breaks up matted grass improves airflow, and allows sunlight to reach the soil, helping dry out the damp conditions. Aeration can further enhance drainage and oxygen circulation.

Apply Fungicides

A fungicide may be necessary for severe snow mold. Products containing active ingredients like chlorothalonil or propiconazole are designed to target the fungi responsible for snow mold. Apply these treatments as directed, in late fall before heavy snowfall or early spring at the first sign of symptoms.

Fertilize with Care

Over-fertilizing in the fall can encourage snow mold on grass. High levels of nitrogen promote lush, thick grass growth, which retains moisture and becomes a breeding ground for fungi. Instead, opt for a balanced, slow-release fertilizer in the growing season to strengthen your lawn.

Preventing Snow Mold on Grass

Mowing your lawn before winter to a height of 2 to 2.5 inches can significantly reduce the risk of snow mold. Shorter grass dries more quickly, improves airflow, and minimizes the amount of surface area fungi can attach to. Other prevention methods include:

• Remove Organic Debris: Clearing your lawn of leaves, twigs, and other organic matter before snowfall eliminates potential food sources for snow mold fungi. Regular dethatching and lawn cleanup can further improve drainage and airflow, preventing fungal growth.
• Manage Snow Accumulation: Redistribute large piles of snow to prevent uneven melting and moisture buildup. Use a snowblower or shovel to spread the snow evenly across your lawn, ensuring no single area remains covered for too long.

While snow mold is not usually fatal to a lawn, it can cause lasting damage if untreated. The fungus weakens grass blades and roots, leaving your lawn vulnerable to other diseases, pests, and weeds. Snow mold also delays your lawn’s spring recovery, resulting in uneven growth and thinning turf.

In severe cases, snow mold can kill patches of grass entirely, requiring reseeding or overseeding to restore the affected areas. Early treatment and prevention are key to protecting your lawn’s long-term health.

Snow mold on grass is a common winter lawn disease caused by fungal growth under prolonged snow cover. By taking proactive steps in the fall and addressing symptoms promptly in the spring, you can keep your lawn healthy and vibrant year-round.

Snow mold may be a nuisance, but with the right care, your lawn will bounce back stronger than ever. Keep your grass healthy, manage moisture, and enjoy a lush, green lawn all season long!