Lawn Care: Solutions for Snow Mold - The Edge from the National Association of Landscape Professionals

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Lawn Care: Solutions for Snow Mold

Spring is well underway and as the snow melts, it may reveal an unwelcome surprise on your customer’s lawn: snow mold.

Snow mold appears as nearly circular patches with the turf inside the circle appearing white, gray or pink and matted together.

It is caused by gray snow mold or pink snow mold, with the pink variation being more severe as it can kill the crown and roots of turfgrass. Gray snow mold typically affects only the grass blades.

Pink snow mold is also not limited to snow-covered turf. It can be found year-round in cool, humid weather.

What Causes It

Fungi Typhula incarnata and Typhula ishikariensis cause gray snow mold and appears when extended snow cover has been present throughout the winter. It requires at least 60 days to develop. It is most severe when heavy snow falls on unfrozen ground. In some cases, it can kill large areas of turf and recovery can be slow.

Pink snow mold is caused by the fungus Microdochium nivale and can form patches even after snow cover is no longer present. It is typically found where there is the greatest snow accumulation. Ideal conditions for pink snow mold are temperatures slightly above freezing at the snow/turf interface and wet leaf tissue.

Perennial ryegrass, annual bluegrass, creeping bentgrass are more susceptible to snow mold, while certain cultivars of Kentucky bluegrass are the least susceptible.

Repairing the Damage

Unfortunately, there are no fungicides that work on snow mold in the spring. The best you can do is rake the affected area to loosen the matted grass and give it time to dry out. Promote new growth in the spring with light fertilization. 

Majority of the time, snow mold is just a cosmetic issue that can be cleared up with proper cultural practices. Because fungus relies on moisture and the right temperatures to continue spreading, warmer spring temperatures can speed a lawn’s recovery.

If the discolored grass never recovers, it is best to reseed the area as soon as weather permits.

Preventing Future Snow Mold

Like most lawn care issues, an ounce of prevention is worth a pound of cure. While there is not much you can do for your client’s snow mold this year, you can work to mitigate snow mold from occurring through a number of cultural practices before and during winter.

Avoid applying large amounts of nitrogen in the fall. Also, make sure the lawn is cut at no more than 3” and no less than 2” tall before winter. This will keep it healthy but not overly thick, which is prone to snow mold. Dethatching in fall can improve circulation in the grass. Cleaning the yard of leaves before snowfall can also be helpful, as damp leaves can provide moisture for the fungi.

If heavy snow is anticipated, minimize the duration of snow cover with snow fences, wind barriers or other structures. Prevent traffic on snow-covered turf, as compacted snow takes longer to melt.

Preventative fungicides can be applied before the snow sets in, but should be reserved for high-value turf such as golf course putting greens, tees, and fairways; sports fields; and recently seeded lawns.

Jill Odom

Jill Odom is the senior content manager for NALP.