Gray snow mold

What is gray snow mold?

Gray snow mold, also called Typhula blight, is caused by the fungus Typhula incarnata. A close relative, Typhula ishikariensis, causes speckled snow mold and needs even longer snow cover. Both attack cool-season grasses, and Purdue considers all cool-season species about equally at risk where snow lasts.

Snow cover is the key. Purdue says snow is required for this disease. The fungus grows best right around freezing, about 32 to 36°F. A deep snow pack keeps the soil surface just above freezing and the grass wet for weeks. Missouri Extension says disease begins 30 to 45 days after a lasting snow cover sets in.

On home lawns and sports turf, the damage is usually skin deep. UMass notes most leaves die but new growth usually comes from the crowns. Purdue says T. incarnata outbreaks tend to be milder and recover faster than the speckled kind, which can reach into the crowns.

Symptoms and signs

• Round, straw-colored to gray patches that appear as snow melts
• Patches about 6 inches to 3 feet across, often merging on long-snow years
• Grass blades matted, brittle and silvery gray to white
• Gray, lint-like fuzz on the blades right at snowmelt that vanishes as the grass dries
• Small round brown seed-like bodies (sclerotia) stuck in the dead blades

Gray snow mold identification: what to look for

• Symptoms: Round, yellow, straw or gray-brown patches. UMass gives 1 to 3 feet across; Purdue gives 6 to 12 inches on short turf, with bigger, fuzzier patches on taller grass.
• Signs: Gray, lint-like fungus on matted blades at snowmelt. It dries up and disappears as the grass dries out.
• Signs: Sclerotia: small, hard, round bodies in the dead leaves. Gray snow mold's are about 2 to 5 mm and tan to reddish-brown. Speckled snow mold's are smaller and dark brown to black.
• Timing: After long snow cover. Purdue's rule of thumb for golf turf: mild damage after 40 to 60 days of snow, moderate after 60 to 90 days, severe beyond 90 days.

Disease cycle

The fungus spends summer as hard little sclerotia in thatch and dead grass. In late fall, when it turns cold and wet, the sclerotia sprout. Some send out threads that attack leaves directly; others grow tiny fruiting bodies that release spores. Under deep snow on unfrozen soil, the fungus keeps growing outward in circles all winter. When the snow melts, the patches show, and new sclerotia form in the dead blades to start the cycle again the next fall.

When to look: Check the lawn as the snow melts in late winter and early spring, especially after a winter with long, deep snow cover.

Gray snow mold look-alikes

A few things get mixed up with it:

• Pink snow mold (Microdochium nivale): Purdue says the two look very alike on lawns, and WSU notes they often occur together. Pink snow mold patches are usually smaller, have a pink edge or pink fuzz, and lack the hard brown sclerotia.
• Speckled snow mold (Typhula ishikariensis): Nearly the same disease, but its sclerotia are smaller and dark brown to black, and UMass says it needs about 75 to 90 days of snow.

How to manage gray snow mold

Cultural control

• Keep mowing until the grass stops growing in fall. Purdue suggests about 2 1/2 inches on lawns so the grass does not mat down under snow.
• Rake leaves and mulch off the lawn before the first lasting snow.
• Avoid heavy late-fall nitrogen. If you feed in fall, use a slow-release product.
• Do not pile shoveled or plowed snow on the same lawn spots every year.
• In spring, rake matted patches to let air in, then overseed thin spots early.
• Improve drainage and keep thatch thin.

Biological control

• Missouri Extension reports that certain strains of a related fungus have shown promise as a biological control, but they are not sold as products yet.

Chemical control

Purdue says fungicides for snow mold are not recommended on home lawns, and Missouri Extension says they are rarely needed there. On golf courses and sports fields with a history of long snow cover, protection has to be on the grass before the first lasting snowfall. UMass says sprays after snowmelt do not work. UMass suggests pairing a contact fungicide with a systemic one, and Missouri Extension notes mixing modes of action helps cover a range of snow molds. Use only products labeled for this use; the label is the law.

Use only products labeled for this disease and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Use snow fences or wind breaks to keep big drifts off important turf.
• Spread out where you pile snow, or pile it off the lawn.
• Plant grass that UMass lists among the least susceptible, such as colonial bentgrass or certain Kentucky bluegrass cultivars, where snow mold is a yearly problem.

When to call a pro

Most home lawns recover with spring raking and a little overseeding. If a golf course, sports field or other high-value turf loses ground to snow mold most winters, talk to a licensed pesticide applicator before the snow arrives. See our pesticide applicator license guide.

Related guides: Weed identification guide · All pests and diseases

Questions about gray snow mold

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