Snow Mold on Grass: Identification, Prevention, and Treatment

If you notice circular patches of lighter colored grass where your snow melted, you could be dealing with snow mold. This common lawn disease occurs in snowy regions of the U.S. 

It’s caused by a couple of common fungi that live in the soil and plant debris in your yard. They cause straw-colored circles in your yard after the snow melts and the temperatures warm up. You may even see patches of gray or pink fungal growth in some sections.

As troublesome as snow mold may appear, there’s no reason to worry. Let’s dive into the ways to identify, prevent, and treat this common fungal infection on your lawn. 

What is Snow Mold?

Snow mold is a common fungal disease that can happen on any species of lawn grass. There are two types of common snow mold infections: pink and gray. 

The fungus Microdochium nivale is responsible for pink snow mold. Typhula incarnata and Typhula ishikariensis cause gray snow mold infections. 

Pink snow mold and gray snow mold caused by Typhula ishikariensis can be more serious. These fungal infections can reach the crown of your plants and be more damaging in the long term. 

Typhula incarnata infections tend to be more common and less destructive. These infections are typically superficial and should go away naturally in spring. 

How Does Snow Mold Occur?

This infection is more common and severe in areas with lots of snow cover. Without heavy snow cover, the infection will ‌be cosmetic. 

The fungi lie dormant in the ground throughout the warmer months in the form of tiny structures called sclerotia. When these masses of hardened mycelium are exposed to cold and wet temperatures under snowmelt, they germinate and expand radially. 

These molds thrive when the ground temperature is between 32 to 36°F (0 to 2°C). If your grass stays wet and cool, the infected spots will grow. Once the sun heats the mycelium, it dries up and forms more sclerotia that will germinate the following winter. 

Symptoms

After the accumulated packs melt, look for circular patches of straw-colored grass. Gray molds cause spots that are between a couple of inches to a couple of feet in diameter. Pink molds are smaller, usually less than 6 inches in diameter. 

The grass blades will be matted and usually tan or even bleached white. They’ll feel crusty and dead when you touch them. 

If you look closely, you may see reddish-brown sclerotia structures growing at the ends of the grass leaves and crowns. This is a telltale sign of gray molds. Sometimes, the fungal mycelium can form into large clusters on the leaves. 

If left untreated, some people may experience allergic reactions to the molds. It’s important to wear a mask while raking infected patches of grass if you suffer from allergies. 

Prevention

Fortunately, there are ways to prevent these infections without damaging your lawn. Proper lawn maintenance and controlling accumulation are usually all you need to do to avoid the worst infections. Below are the best cultural practices to prevent more serious infections. 

Mow Your Lawn Well Into the Fall

It may sound simple, but mowing your lawn well into the fall can have a big impact. Grass left growing tall provides the layer of cool and moist air these fungi thrive in. 

Cut your blades down to ½ an inch. You can even go shorter if your ground cover is healthy and well-established. 

Continue mowing your lawn well into the fall, just before the first heavy snowfall. This will give your grass less time to grow before winter. 

Rake and Remove Leaves in the Fall

Many sclerotia hitch a ride on leaves and plant debris. Leaves also provide insulation to create pockets of ideal temperatures under the accumulated packs. 

Just before the first dusting, rake up all the fallen leaves in your yard and dispose of them. Keep your grass completely clear and you should see a noticeable change the following season. 

As mentioned before, be extra careful if you suffer from allergies. Try wearing a mask for extra protection. Most reactions are mild but can be irritating. 

Avoid Nitrogen Fertilizers in the Fall

Nitrogen fertilizers may increase the spread of these mycelia under the accumulated packs. The extra nutrients create well-fed fungi that spread even faster. 

Stop fusing nitrogen-heavy fertilizers in the fall. If you do have to fertilize, only feed the plants that need it. 

Keep Snow Banks Away

Snow molds thrive in grass under heavy snow piles. There isn’t much you can do if you live in areas with heavy annual accumulation. However, in many regions, people pile snow in their yard, which can increase the chances of severe infections in their grass. 

If you have excessive piles, move them out to the street or sidewalk. Keep them from forming on your grass by setting up barriers for it to collect in. This simple step can make a big impact. 

You Can Use Fungicides

The methods above are much safer for the environment and should work wonderfully. However, you can prevent snow mold infections on your grass by using preventative applications of fungicide. 

Try using natural organic fungicides instead of harmful chemicals. There are plenty of DIY fungicide recipes out there and many of them work. 

Spray the fungicides on your grass just before the first solid dusting in winter. If you wait until after the winter precipitation accumulates, the fungicide won’t work. 

Treatment 

If you notice infections on your lawn, there are a few things you can do to treat them. The first step is raking your grass. Gently rake around the circular areas, trying not to damage the healthy plants. 

Raking helps spread the mycelium out and exposes it to the sun. The fungi will slowly dry up over time, freeing your plants. In most cases, new healthy growth will appear from the crowns in spring. 

In serious cases, you may have to reseed your lawn. This is rare and usually your lawn will recover just fine. The infected areas may grow back slower than the rest of your lawn.