Snow Mold

As the extended snow cover from last winter melts from twin cities metro lawns, evidence of gray and pink snow mold disease became apparent. Snow molds are fungal diseases that flourish under snow, especially when the ground is not thoroughly frozen and snow cover is present for extended periods. Snow molds are named for the webby material that grows over circular patches of matted grass. (Photo1).

Gray snow mold has been prolific this year and probably makes up over 60 percent of the affected turf this spring. Susceptible turf species are bluegrass, fescues, ryegrass and mainly bentgrass. Gray snow mold is caused by the fungus Typhula incarnata and other Typhula species. Yellow to white circular patches of damaged turf are visible right after snow melt (Photo 2). Patches vary in size and may overlap to blight large areas of turf. The fungus produces yellow/orange structures (Photo 3) called sclerotia that when mature are dark-brown to black color, are easily visible and persist through the summer and in late fall. These structures start colonizing grass leaves again 30-45 days after permanent snow cover has left. Gray snow mold damage occurs in winter and early spring. The best thing you can do for grey snow mold, aside from improving your soil aeration and bioactivity is to lightly fluff up the dead grass with a rake. This will allow it to dry more completely and will also allow the sunlight to reach the soil and promote new grass growth. This disease rarely kills the grass and fungicidal treatment is not warranted. If lawns are being reseeded consider planting resistance turfgrass cultivars.

Pink snow mold can be more problematic. Pink snow mold remains active much longer than grey snow mold. It can continue to go until temperatures get into the low 60’s. Pink snow mold is caused by the fungus Microdochium nivale (Photo 4), which produces roughly circular bleached patches ranging in size from 1-8 inches in diameter. The patch will appear red-brown and water-soaked at first then later turn pinkish white with red-brown border (Photo 5). You can see this easily in the morning when there is dew on the ground. As with the grey snow mold, you should lightly rake or fluff up the pink snow mold to allow air and sunlight to the soil. With this type you should be careful to not spread the disease by using the rake on the rest of the lawn. After you rake the pink snow mold you should clean your rake with some alcohol or an anti-bacterial soap.

The following steps can be taken to minimize damage in future years:
-Avoid excessive applications of nitrogen fertilizer in the fall.
-Continue to mow the lawn at the recommended height until it is no longer actively growing. The taller the grass, the more likely it will mat down and encourage snow mold development.
-Rake up leaves in the fall.
-Manage the thatch layer to avoid accumulations of more than ½ inch.
-Spread out large snow piles to encourage rapid melting. Use snow fencing to minimize snow accumulation in problem spots.

Photo 1

Photo 2

Photo 3

Photo 4

Photo 5

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