It has been nice to see grass begin to appear around yards, in between snow storms. Granted, when we see grass it is still brown to a sickly yellow, but I was beginning to think that we no longer had anything under all that snow. As we begin to see more grass appear and as the snow disappears we might see some problems with our lawns that I wanted to bring up this week.
As the spring progresses we might see areas with fluffy mycelium in our lawns, especially in areas with matted grass and melting snow. This mycelium reminds me of what a white mold looks like essentially and is referred to as a snow mold. There are two types of snow mold, gray snow mold and pink snow mold. They are fungal diseases that appear in lawns as straw colored circular patches, which continue to enlarge as long as the grass remains wet and cold. Snow molds usually do not occur every year, but are more common when an early snow cover doesn’t allow the ground to freeze.
Gray snow mold is active at temperatures slightly below freezing and up to about 45°F or as long as the lawn stays wet and cool. Fungal growth begins in the late fall or early winter underneath the snow on unfrozen ground. When the snow begins to melt, gray or white patches will appear with webby material. The fungus will then begin to form yellow structures that turn dark brown when mature, known as sclerotia. Sclerotia will survive hot summer temperatures in soil or in plant debris. In the fall, the cycle begins again as the sclerotia begin to germinate and colonize the lawn.
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| Gray snow mold. Photo courtesy of maine.gov |
Pink snow mold is active at temperatures from approximately 32°F to 60°F. Just like gray snow mold, fungal growth begins under snow cover on unfrozen ground. In the spring, white or pink circular mycelium patches will form on the leaf blades. At the center of the patch, spores will be produced that can be dispersed by heavy rains and cultural practices. Unlike gray snow mold, pink mold can occasionally form without snow cover in wet, cool, matted grass.
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| Pink snow mold. Photo courtesy of maine.gov |
To manage these diseases raking the matted area will help to promote drying and warming up of the lawn, which will slow down or eliminate further development of the disease. This is best done in the spring. Fungicides are usually not recommended. Snow mold damage is seldom serious in the urban setting and the infected areas will only take a little longer to green up. Snow molds can easily be prevented by avoiding excessive nitrogen applications in the fall, raking up leaves in the fall, and mowing grass at recommended heights until it is no longer actively growing. Try to avoid piling up snow onto the lawn. With our winter, I know that has been difficult, if not impossible. However, it is something to consider in the future.
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