What do you do if the snow melts off your lawn and leaves white, gray, or pink patches behind? These are signs of snow mold, a type of fungus that affects grass in areas of the country that get a lot of snow in the winter. While it’s unsightly, it’s not the destructive force you might fear, and there are some simple steps you can take to keep it from infecting your lawn come early spring.

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What is Snow Mold?

Snow mold is a lawn disease caused by a fungus that both looks like snow and tends to infect grass as actual snow melts. As temperatures start to warm after the winter, you may either see the mold itself or straw-colored spots of grass that the mold has killed. The fungal spores actually live in the soil all year round, but they remain inactive in extreme temperatures. When the temperature gets to be between 32 and 45°F and melting snow drenches the soil, the spores sprout and spread.

What Types of Snow Mold Are There?

There are two types of this fungus, both of which tend to cause multiple circular bare patches on lawns:

  • Pink snow mold, also known as Fusarium patch, is whitish-pink in color.
  • Gray snow mold, also called Typhula blight, is white to grayish-white.

Both types of mold cause the grass to die and can trigger allergies in people. Pink snow mold is the more serious of the two, as it can kill grass roots as well as blades. It can also remain active and spread in temperatures up to 60°F. Your grass may re-grow after an infestation of gray snow mold, but not after pink.

What Kinds of Grass Does Snow Mold Affect?

Snow mold can grow on any type of cool-season turfgrass that is covered by snow for long periods of time. However, according to the University of Illinois’ Integrated Pest Management Department, certain grasses like bentgrass are more susceptible to this fungus. Kentucky bluegrass, the most popular cool-season grass, is moderately affected, but fine fescue has more resistance to snow mold than other types.

How Do I Remove Snow Mold From My Lawn?

Here’s the bad news: Once you see the snow mold, the damage is already done. Applying fungicide—that is, special chemicals that kill mold—won’t help at that point. The most you can do is gently rake the area to loosen up any matted snow mold grass and allow the soil to dry more quickly.

Once the weather warms up and the soil dries, you’ll have a better idea of how much grass has been affected. Remember that gray snow mold doesn’t kill the roots, so your grass may bounce back from it. For any areas affected by pink snow mold, rake away dead grass and re-seed bare patches.

How Do I Prevent Snow Mold From Growing?

As you may have guessed, the true key to removing snow mold is to prevent it from growing in the first place. Here are some dos and don’ts for preparing your lawn in the fall before the snow hits.

  • DO mow before the first snow. Cut the lawn slightly shorter than normal so that the grass and soil will trap less moisture. Also, consider bagging up your lawn clippings so that they don’t keep the ground damp.
  • DO apply a preventative fungicide. If you know your lawn is particularly susceptible to snow mold, treat it with a specialized product before the heavy snow sets in.
  • DO dethatch your lawn two or three times a year. Some types of grass produce more thatch than others, so make sure to keep the thatch layer at less than ¾”.
  • DO make sure your lawn has proper drainage. Anywhere water pools can create a breeding ground for snow mold, so fill in any low areas with topsoil.
  • DON’T fertilize in late fall. Cool-season grasses go dormant in the winter by letting grass blades dehydrate, making them less susceptible to mold. They will revive themselves naturally in the spring. Don’t interrupt this process by fertilizing within about six weeks of the first expected snowfall.
  • DON’T let leaves or snow pile up. Anything that traps moisture is bad news for grass, so rake up leaf piles in the late fall. Similarly, when shoveling driveways or sidewalks, try not to create large piles of snow that will take a long time to completely thaw.

Restoring Your Lawn

If you find yourself with snow mold in the spring, don’t worry—it will typically resolve itself as temperatures warm up. The snow mold fungus will stop growing when temperatures are between 45 and 60 degrees and the soil starts to dry out.

Until then, if you’re tired of seeing unsightly patches on your lawn, you can gently rake over those areas to dry them out more quickly. Apply new grass seed to repair those spots. And avoid adding fertilizers or fungicides at this point, as they won’t help, and will only weaken your lawn as it’s attempting to heal itself.

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