What is Snow Mold Lawn Disease?

As winter draws to a close and the weather finally starts to show signs of warming up, you may find yourself wanting to start enjoying your outdoor living space again. But getting your lawn in shape after a long winter might take a bit of effort — especially if your grass has been under the snow for a while. In many regions, the wet, soggy conditions characteristic of early spring provide the ideal environment for a lawn disease known as snow mold to take hold. 

Here, we’ll explain what snow mold is and what causes it. You’ll also learn a bit about the different signs and characteristics of snow mold on grass and discover what TruGreen® can do to help keep this lawn disease at bay.

Snow mold isn’t one thing. Rather, it’s the name given to a group of similar lawn diseases that thrive in cool, wet conditions. All snow mold is caused by fungi, but the type of fungus varies depending on a range of factors, such as your grass type, soil condition and where you live. The two most common types of snow mold disease that occur on turf during cold weather conditions are pink snow mold (Microdochium patch) and gray snow mold (Typhula blight). 

Unlike most lawn diseases, which prefer the warmer temperatures of spring and summer, snow mold thrives in cooler temperatures. Gray snow mold generally develops when snow cover remains for an extended period of time. Once the snow cover melts in the late winter or early spring, the fungus proliferates, causing telltale signs of disease (more on that shortly). Pink snow mold does not require snow cover to develop as it also proliferates when the grass is wet and temperatures are below 45 F.

Because snow mold only occurs on grasses that are actively growing in cooler weather, it is not typically found on warm-season lawns that experience periods of winter dormancy. However, some types of snow mold can survive at normal springtime temperatures (up to 60oF) if the air and soil are moist for a prolonged period of time. Spores are spread by the wind or splashing rain, causing the disease to spread from one area of your lawn to another.

As mentioned previously, there are different types of snow mold homeowners may face. Two of the most common are pink snow mold (also known as Michrodochium patch) and gray snow mold (Tyhpula blight). 

Pink Snow Mold

• Develops when the grass is wet and temperatures are below 45 F.
• Does not require snow cover but may be very destructive under snow, particularly if the grass has not hardened off before the first snow.
• Affected areas generally measure 6 to 12 inches in diameter, and may have a pinkish mycelia (fungus) growing around its edge

Gray Snow Mold 

• Occurs in regions where snow cover remains throughout the winter.
• Affected areas have a matted appearance and are circular in shape, ranging from a few inches to up to 2 feet in diameter.
• These areas may coalesce (grow together), and extensive damage may appear on the turf when the snow melts.
• Gray snow mold produces round hard structures called sclerotia on affected leaves. These ball-like structures are visible to the naked eye and can help distinguish gray snow mold from pink snow mold (do not have sclerotia).

There’s no 100% foolproof way to prevent snow mold lawn disease, save for moving somewhere that’s warm, dry and sunny year-round. That being said, there are things you can do to make your lawn a less hospitable place for this unwanted cool-weather disease.

Mowing your lawn short (2-2.5”) for the last time in the fall can help reduce snow mold because shorter blades have less tendency to mat down compared to longer grass blades. Also, avoiding excess nitrogen fertilizer applications in the late fall and ensuring your soil drains properly to prevent excess moisture, can help make your lawn a less attractive place for fungus. 

Finally, remember that many species of snow mold favor excessive thatch. If your lawn is prone to thatch, consider undergoing a TruGreen Aeration & Overseeding service in the late summer or fall. During this service, your TruGreen lawn care expert will use a tool called an aerator to break up thatch and compacted soil. Then, they’ll overseed your lawn to help fill in any bare areas or thinning patches.

Snow mold rarely causes severe damage. If you spot this disease on your lawn in the early spring, the best thing to do is gently rake affected areas to aid in recovery. Raking will help remove matted grass, aid in air circulation, and stimulate new grass growth. If you find your grass still doesn’t look as healthy as you’d like, your TruGreen lawn care expert can develop a tailored plan designed to get your lawn back in shape.