What is Snow Mold?

Spring lawn grass affected by grey snow mold Typhula sp. in the April garden

Snow mold is a group of sneaky fungal lawn diseases that mostly attack cool-season lawns when covered in snow for a prolonged period. 

Fortunately, the damage is usually moderate and can be limited with proper lawn care. We discuss snow mold signs and causes so you can identify the damage quickly and speed up lawn recovery in the spring.

What Causes Snow Mold?

snow mold in lawn
Photo Credit: noricum / Flickr / CC BY-SA 2.0

Snow molds are turf diseases caused by cold-resistant fungi that thrive under prolonged snow cover. When spring rolls in and the snow melts, they leave the once-green grass patchy, matted, and needing attention.

How Snow Mold Develops 

Fungi travel through wind, rain, lawn care equipment, and even shoes. They stay dormant in the thatch layer during the warm season and activate in late fall when the weather is right. These fungi thrive in: 

  • High humidity
  • Cool temperatures just above freezing (32 to 45 degrees Fahrenheit)

Top Causes of Snow Mold

Whatever keeps your turf wet and lush during the winter can kickstart a nasty snow mold infestation:

  • Piles of snow on the lawn
  • Organic debris like thick thatch, piles of fallen leaves, thick mulch, and tall, matted grass
  • Compacted soil that traps moisture
  • Watering the lawn too much in the fall
  • Lush grass that has not hardened for winter due to low potassium levels in soil, late fall applications of high-nitrogen fertilizer, or a warmer-than-usual autumn

Susceptible Turfgrasses

All cool-season grasses are susceptible to snow mold, but some experience less damage and recover faster. 

  • Moderate to poor snow mold resistance: Kentucky bluegrass, tall fescue, and perennial ryegrass
  • Good snow mold resistance: Fine fescues, particularly hard and creeping red fescue

Snow mold can also attack bermudagrass and zoysia lawns in the transition zone.

Pro tip: If you often deal with snow mold damage, overseed with a mix of fine fescues.

Types of Snow Mold

Two common types of snow mold infest home lawns and golf courses: gray and pink snow mold.

Gray Snow Mold (Typhula blight)

Gray snow mold, caused by the fungi Typhula incarnata and Typhula ishikariensis, usually requires extended snow cover to develop — at least 60 days, say experts at North Carolina State University.

It is more common in regions of the United States with long, snowy winters, such as: 

  • Northeast U.S.
  • Great Lakes Region
  • Rocky Mountains Region
  • Upper Midwest

Damage: 

  • It only affects the grass blades.
  • Grass recovers by late spring with proper watering and fertilization.

Pink Snow Mold (Microdochium patch or Fusarium patch)

Unlike gray snow mold, the Microdochium patch does not require snow cover to develop. It is caused by the fungus Microdochium nivale, which also spreads during humid, overcast weather and can grow in warmer temperatures, up to 60 degrees Fahrenheit. 

You’ll find it next to the gray mold in regions with heavy snow winters – where pink snow is most severe. But this type of snow mold is also present in areas with a wet, mild cold season, such as: 

  • Pacific Northwest 
  • Northern Coastal Regions
  • Midwest in the transition zone
  • Southern states at high elevations

Damage: 

  • It infests grass blades, crowns, and roots.
  • It can cause severe damage in favorable conditions, killing the grass and requiring overseeding in the spring.

Signs of Snow Mold

Snow mold on turf
Photo Credit: Maasaak / Wikimedia Commons / CC BY-SA 4.0

Scout your lawn for signs of snow mold as soon as the snow melts. This is the best time to identify infected areas. Look for:

  • Pink snow mold: Circular patches of bleached white to tan grass with a pinkish hue or reddish edge, up to 1 foot wide.
  • Gray snow mold: Circular patches of whitish, straw-like grass with a grayish, silvery tint, up to 3 feet wide.

Inside these patches, the grass looks matted and brittle. You also might notice mycelium (fine fungal strands) near receding snow banks and where the soil is very wet. It looks like a whitish, matted spider web engulfing the grass leaves.

Tip: Snow mold patches are typically circular, well-defined, and easy to spot, but they might merge into a single extensive area if snow cover persists for several months. 

Why is Snow Mold Bad for Your Lawn?

Snow mold makes spring lawns look bad. Instead of the lush, green young grass you expect, the lawn fills with bleached, matted patches. It’s harsh on the eye and takes additional work to get healthy in the early season.

Fortunately, the damage is typically minor to moderate and rarely leads to turf death. According to professor Paul Koch, a turfgrass pathologist at the University of Wisconsin-Madison and an expert in snow mold, once the weather warms up and turfgrass starts growing, damaged plants recover within a few weeks. 

“This makes it [snow mold] less damaging than other common summer diseases like summer patch.” 

Snow mold also can trigger nasty allergies and make spring lawns unsafe for sensitive people and pets. Inspiring the fungi and spores in the air can lead to sneezing, a runny nose, and itchy eyes and can worsen chronic respiratory diseases like asthma. 

How to Get Rid of Snow Mold

Raking the infected patches is the best way to get rid of snow mold in the spring. This simple action lets fresh, warmer air dry the grass and exposes the mold to sunlight, killing it faster. 

Here’s how to rake snow mold patches for the best results:

  • Allow the soil to dry slightly before raking. If the soil is too wet, you risk removing the grass with roots and compacting the ground.
  • If you suffer from allergies, wear a safety mask or hire a lawn care professional to do this task. Keep dogs, kids, and any family members with allergies off the lawn while you are working.
  • Gently rake the patches with a garden rake. They might hide new growth, and you don’t want to damage it.

Is There Any Way to Prevent Snow Mold?

There is no bulletproof method to prevent snow mold from growing on your lawn, but if you prepare the lawn for winter the right way, you can reduce fungal spread and limit grass damage:

  • Ensure good drainage and maintain a pH of 6.5 to 6.9 (snow molds thrive in alkaline soil with a pH over 7.0).
  • Go easy on the nitrogen in late fall, but ensure enough soil potassium to improve cold hardiness.
  • Account for rainfall, and don’t waterlog the soil in the fall.
  • Mow the lawn 2 to 3 inches tall, depending on the turf type, about a week before the first frost or snow. 
  • Apply preventive fungicides in late fall before the first snow.
  • Minimize snow piles on the lawn and use fences or windbreakers to limit snow drifts.
  • Choose resilient turf types such as fine-leafed fescues.

Keep Snow Mold Under Control!

A well-maintained lawn is the best defense against snow mold. Find a lawn care professional with LawnStarter and make sure your turf enters the winter clean, healthy, and strong, ready to bounce back in the spring!

Main Photo Credit: maykal / Adobe Stock Free / License

Sinziana Spiridon

Sinziana Spiridon

Sinziana Spiridon is an outdoorsy blog writer with a green thumb and a passion for organic gardening. When not writing about weeds, pests, soil, and growing plants, she's tending to her veggie garden and the lovely turf strip in her front yard.