How to prevent turf disease under snow cover

Snow creates an ideal environment for fungal diseases in grass
Snow cover creates a dark, humid environment that fungus thrives on.

Some landscapers trade lawn mowers for snow blowers during the winter months, but that doesn’t mean they can slack off on lawn care. Turfgrass is susceptible to a variety of issues that can plague professionals come spring.

[Related: 5 fall steps for healthy spring lawns]

Proper treatment of diseases like pink or gray snow mold will begin before the first snow.

Pink and gray snow molds are caused by fungi that lie dormant in soil and thatch, according to the Center for Turfgrass Science at Penn State. Snow cover creates a dark, humid environment for spores to germinate. When the snow melts away, the fungi appear in patches in the lawn.

Pink snow mold leaves tell-tale pink mycelia and sporodochia on grass, while symptoms of gray snow mold include dead, bleached or matted grass with hard, pin-sized sclerotia embedded in the leaves and crowns of grass, according to the Center.

Pink snow mold can be more severe than gray snow mold, the Center notes, because the fungus that causes it can attack the leaves, crowns and roots of grass.

Although it helps, the fungus that causes pink snow mold doesn’t require snow to thrive. A 2002 article by Jenifer McBeath at the University of Alaska, Fairbanks, and published by the American Phytopathological Society, found that “alternate thawing and snow cover, repeated frosts, cold fogs and light drizzling rain result in particularly favorable conditions for leaf-to-leaf spread of the fungus.”

Alec Kowalewski, assistant professor and turfgrass specialist at Oregon State University, offered some suggestions for preventing snow mold.

“Be sure to remove tree leaves and other organic matter that may have accumulated on your grass,” Kowalewski said. Similarly, “reduce the mowing height just prior to snow fall to minimize organic matter under snow cover.”

Kowalewski also urged lawn care companies to avoid using fertilizer on lawns in the weeks before snow is expected.

“Allow for at least 14 days prior to estimated snow fall date,” he said. The APS found that grasses that are high in nitrogen are more susceptible to snow mold, while higher potassium levels “tend to suppress the disease.”

If professionals do find snow mold, Kowalewski recommended applying fungicides that have at least three active ingredients or modes of action.

While the weather itself poses challenges for protecting turf, the way we deal with snowy weather presents problems, too.

[Related: Snow removal goes gig—Yep, there’s an app for that]

Rock salt can damage grasses, and Kowalewski recommends not using it.

“Don’t use rock salt,” he said. “Instead use calcium-based products, such as calcium-chloride.”

One thought on “How to prevent turf disease under snow cover

  • March 16, 2019 at 1:18 pm

    Pink snow mold rarely occurs in Colorado home lawns, and gray snow mold only appears where the has been 60+ days of continuous snow cover. We (Colorado State University and CSU Extension) never recommend fungicides for snow mold in home lawns – preventatively or creatively – because snow mold in home lawns rarely causes anything more than temporary cosmetic injury.


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