Do you know when you should think about snow mold control?

October 31, 2023 -  By
Gray snow mold develops under snow cover. The longer the snow cover, the larger the patches. (Photo: Paul Koch, Ph.D.)

Gray snow mold develops under snow cover. The longer the snow cover, the larger the patches. (Photo: Paul Koch, Ph.D.)

Gray snow mold can affect almost any cool-season turf species if it experiences long periods of snow cover. As snow melts, lawn care operators (LCOs) see its signs.

How to identify

Gray snow mold develops under extended deep snow cover and becomes evident as it melts, says Matt Giese, technical field manager for Syngenta. Appearing as light brown, gray or bleached patches, it can range in diameter from a few inches to nearly 2 feet.

“The longer the snow cover, the larger patches become,” Giese says. “Sparse to dense amounts of grayish mycelium may be seen on blighted tissue in the presence of melting snow.”

The leaves become matted and appear small pinkish-white to reddish-brown in color —sometimes black. Masses of sclerotia may be seen on and/or embedded in blighted leaves.

“Sclerotia become shriveled when dry and may be so numerous as to give matted patches a speckled appearance,” he says.

Gray snow mold can be challenging to manage since the infection process occurs in cold temperatures under snow cover, and visible symptoms aren’t generally seen until the spring when the snow melts.

“Additionally, fungicide treatments are not effective at suppressing this disease in the spring after the snow has melted,” Giese says. “As a result, unsightly damaged areas can persist well into the summer months before full recovery occurs.”

LCOs should consider the duration of the snow cover and turf damage in the spring in their areas to determine if preventive control measures are needed.

“The best strategy to reduce or prevent damage from this disease is to plan for fungicide applications in the fall after mowing has ceased but before permanent snowfall occurs,” Giese says.

Systemic fungicides that move into the plant and protect it from the inside out are effective treatment options for various snow mold species, Giese says.

“Raking the matted areas to remove dead leaf tissue and to open up the turf canopy can aid recovery as warmer temperatures arrive and stimulate plant growth,” Giese adds.

Time applications carefully

Gray snow mold can become problematic when there are more than 45 days of snow cover, says Aaron Hathaway, technical services manager in turf and ornamentals for Nufarm. Though it isn’t a commonly devastating disease in lawn-height turf, he adds.

“In areas of the U.S. that can commonly drop and maintain this much snowfall, the potential to see damage from gray snow mold the following spring after the snow has melted is there,” Hathaway says.

Turf symptoms can look like circular spots or patches of coalesced spots. Sclerotia, small fungal survival structures, may also be found in the spring within the dead leaf tissue, Hathaway says.

Prevention is key in areas with prolonged snow cover, so LCOs must apply a fungicide before snowfall to prevent the development of gray snow mold.

“However, these fungicide applications are most effective when applied to the turf as late in the season as possible so that higher concentrations of the fungicide remain on and/or in the plants for as long as possible after snow falls,” Hathaway says.

Gray snow mold also can develop under large piles of snow accumulating from plows moving snowfall into the same spot during the winter.

“If these areas are known, a preventative spot treatment could be in order,” Hathaway says.

When there is damage, the turf can quickly recover as temperatures increase, especially when LCOs provide adequate fertility, he adds.

“If and when symptoms are noticed in the spring, communicate with clients that the turf will recover and provide good cultural practices so that recovery is as quick as possible,” Hathaway says. “In the rare, high-pressure situations where snow mold could actually kill large portions of lawns, spring reseeding will be necessary.”

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