Pink snow mold

What is pink snow mold?

Pink snow mold is caused by the fungus Microdochium nivale, once called Fusarium nivale. When it shows up without snow it is called Microdochium patch or Fusarium patch. Purdue says all cool-season grasses can get it. It does the most harm on golf course bentgrass and annual bluegrass, but on home lawns it is most common on Kentucky bluegrass and perennial ryegrass mown at 3 inches or taller.

The fungus likes it cold and wet. UMass says it grows from near freezing up to about 60°F and is favored by repeated frosts, cold fog and slow drizzle. UC IPM notes air above 70°F stops it. Snow helps by keeping grass cold, wet and matted, but Purdue stresses that snow is not needed for heavy infection.

The fungus blights the leaves but, per Purdue, is not reported to attack the crowns or roots. That means most home lawns recover once the weather warms and dries. Raking matted spots in spring helps the grass bounce back.

Symptoms and signs

• Round spots, usually under 8 inches across, that start water-soaked and orange-brown to reddish-brown
• Spots fade to light gray, tan or bleached white, often with a pink or reddish-brown edge
• White to pink fuzzy fungus on the blades in cool, wet weather or right as snow melts
• On taller lawns, mats of dead, stuck-together grass without a clear circle
• On golf greens, streaks that follow the path of draining water

Pink snow mold identification: what to look for

• Symptoms: Small, round spots, usually under 8 inches. They start water-soaked and orange-brown to dark reddish-brown, then fade to light gray or tan. At snowmelt they look bleached white to tan, often with a pink rim.
• Signs: Pink spore masses in a mat of fungus on wet blades. White fluffy fungus may cover spots under snow or in very wet weather. Missouri Extension says the pink color comes partly from tiny white-to-pink fruiting bodies.
• Symptoms: On taller-cut lawns, Purdue describes patches of dead, matted blades that often have no clear round shape.
• Timing: Fall, winter and spring during cold, wet spells. Purdue gives an active range of about 30 to 60°F. In Pennsylvania, Penn State sees the snow-free form in early to late spring.

Disease cycle

The fungus rests through summer as dormant threads in thatch, dead leaves and soil. In cool, wet weather it grows out and infects the leaves. Spots grow outward in circles. Tiny pink fruiting bodies on dead tissue release spores that spread in splashing or running water, on mowers, and on shoes. Long-lasting snow on unfrozen ground, matted grass and heavy late-fall nitrogen all make it worse. Warm, dry, sunny weather shuts it down.

When to look: Look right as snow melts in late winter and early spring, and during long cold, wet spells in fall and spring.

Pink snow mold look-alikes

A few things get mixed up with it:

• Gray snow mold (Typhula incarnata): Purdue says the two look very alike on lawns, and UMass notes they can occur together. Gray snow mold patches are larger (about 1 to 3 feet), have gray fuzz, and leave small hard brown bodies (sclerotia) on the blades.
• Red thread (Laetisaria fuciformis): Also pinkish, but shows in mild, wet spring and fall weather with red thread-like strands on leaf tips.
• Pythium blight (Pythium aphanidermatum): Missouri Extension notes the two have been confused, but Pythium blight is a hot-weather disease.

How to manage pink snow mold

Cultural control

• Skip heavy, quick-release nitrogen in late fall. Feed a few weeks before dormancy with slow-release forms.
• Keep mowing until the grass stops growing so it does not go into winter long and floppy.
• Rake leaves off the lawn through fall.
• Do not pile shoveled or plowed snow on the same lawn areas every year.
• Rake matted spots in spring to dry them out and help regrowth.
• Keep thatch in check and improve drainage.
• Keep soil pH near 6.5 and potassium adequate, as UMass and UC IPM suggest.

Chemical control

Purdue says fungicides for snow mold are not recommended for home lawns. On golf courses, protection is applied in late fall before snow; UMass notes sprays made after snowmelt do not work. Extension guides list several fungicide groups for this disease, and Missouri Extension warns that not every product for pink snow mold also controls gray snow mold. 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 barriers to stop big drifts from sitting on turf.
• Keep foot and vehicle traffic off snow-covered lawn to avoid packing it.
• Give a light feeding in spring to push new growth.
• Reseed any spots that do not fill back in.

When to call a pro

Most home lawns recover with spring raking. For golf greens or sports turf with a history of snow mold, talk to a licensed pesticide applicator before winter. See our pesticide applicator license guide.

Related guides: Weed identification guide · All pests and diseases

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