Several savvy gardeners have asked me if local lawns will be damaged by snow molds this year because of the persistent snow. It is not a sure bet, but snow molds may definitely be a problem this spring.
For those of you who do not know about snow molds, they are fungus diseases that infect turfgrass. There are two main types of snow mold: gray and pink. Gray snow mold growth is favored when unfrozen turf is covered by snow for relatively long periods of time. Pink snow mold is favored by cool, wet conditions in the early spring and fall, and is also promoted by repeated freezing and thawing.
Pink snow mold (Monographella nivalis) is most severe on bentgrass and annual bluegrass, but can infect Kentucky bluegrass, fescues and perennial ryegrass. It tends to be a greater problem on turf that is shaded or mowed too low.
The first symptoms of pink snow mold are somewhat circular, water-soaked, 2-inch spots that turn reddish brown to light gray or tan. Infected patches can enlarge to become a foot across.
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The pink in the name is because the mycelia, or strands of the fungus on the outer edges of the patches, may appear pinkish to white early in the day. Grass within the spots can become matted from heavy mycelium growth.
There are two main types of snow mold: gray and pink.
Keep in mind that pink snow mold does not need snow cover to develop, but tends to be active in many areas as snow starts to melt in early spring. Two years ago, a number of local lawns were damaged by an early spring infection of pink snow mold. That year, there was very little snow cover, but rain, fog and cool weather dominated.
Gray snow mold (Typhula incarnata and Typhula ishikariensis) is caused by several different fungi. These fungi develop under prolonged snow cover when the turf beneath is not frozen. The longer the snow cover, such as beneath snow piles or drifts, the worse the infection. When the snow finally melts, round, yellow to brown, 3- to 6-inch patches start to develop. The gray to white web-like mycelia of the fungus mat down the grass in those patches. Once warmer drier weather persists, the mycelia dry up, leaving behind a crusty surface.
Keep in mind that pink snow mold does not need snow cover to develop, but tends to be active in many areas as snow starts to melt in early spring.
The bad news is that infected areas of lawns will look pretty sad if pink or gray snow mold has been attacking the grass. The good news is that the molds usually only kill the leaves, not the crowns or roots of the grass plants. This allows the plants to regrow with warmer, drier weather. Because of this, chemical control for snow molds is not recommended for home lawns, plus fungicides that are effective for snow mold control are applied in the fall.
Once the snow melts and things dry out and warm up, check to see if your lawn shows evidence of snow mold. If so, rake the affected area of lawn to remove any mycelial crust. With warmer weather, those spots will usually come back. If not, consider raking and reseeding the bare patches.
Gray snow mold develop under prolonged snow cover when the turf beneath is not frozen.
To help prevent snow mold in the future, pay attention to lawn care practices. Keep mowing in the fall until the grass stops growing. Maintain a balanced lawn fertilization program throughout the season. Avoid applying excessive nitrogen in the fall. Remove thatch and relieve soil compaction as needed. Be sure to rake up leaves in the fall before snow covers the lawn.
The only thing we can do now is to remove any big piles of snow on lawn areas and hope that snow mold will not show up when it all melts.
Marianne C. Ophardt is a retired horticulturist for Washington State University Benton County Extension.