Growing Green: Snow Mold Prevention Begins in Autumn
Can we expect snow mold damage in our lawns next spring? The answer to this question is dependent on the snow and soil temperature conditions this fall and winter. Snow mold is common during years when an early, deep snow cover prevents the soil from freezing. As the snow begins to melt in the spring, matted circular straw-colored patches of grass appear in lawns.
The fungi that cause snow mold to develop become active at temperatures near freezing, and typically develop under a blanket of snow on unfrozen ground. Snow mold fungi may continue to infect home lawns after the snow melts, as long as conditions are cool and wet. As the temperature begins to rise and the lawns begin to dry, snow mold fungi become inactive. Therefore, there is no need for chemical controls unless there is an area on the lawn where the snow mold appears every year.
There are two different types of snow mold: pink snow mold and gray snow mold, each caused by a different fungus. Either of the snow mold fungi typically appears within the home lawn as circular straw-colored patches of grass. These patches usually appear matted and are often covered by white, pink, or gray fungal growth, which has a webby appearance. Pink snow mold produces pink colored spores and pinkish colored fuzzy mycelium while gray snow mold produces sclerotia which appear as dark colored hard spherical bodies on the grass blades.
Although the damage from snow mold is seldom serious, we have had years in which large areas of lawns are killed. Generally, infected areas are just a little slower to green up. Gently rake affected areas of the lawn to promote drying and prevent further fungal growth.
To minimize snow mold damage, avoid excessive applications of nitrogen in the fall. If snow mold is common in your lawn, skip the fall fertilizer application. 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 and encourage snow mold. Do not, however, cut the grass shorter than 2 inches. Grass that is cut too short will be subject to winter injury in the event of a cold, open winter.
Rake up leaves in the fall as a heavy layer of leaves causes a cool, wet environment that encourages snow mold in the spring. As the snow begins to melt in the spring, break up and spread out large snow piles to encourage rapid melting. If you have problem spots in your lawn, consider using snow fencing to minimize snow accumulation in those spots.
For more information about snow mold, visit the University of Minnesota Extension website at:
Robin Trott is a Horticulture Educator with University of Minnesota Extension.