Gray snow mold, also referred to as "Typhula blight", is caused by two species of fungi in the genus Typhula. These fungi thrive when moisture is plentiful and when prolonged periods of snow cover exist, especially after the snow falls on unfrozen ground. Gray snow mold has been common on Iowa lawns and golf courses this month.
Symptoms of this disease become evident as the snow melts. The leaves in the affected areas are matted together and have a silver-gray, crusted appearance as the grass dries. Affected areas vary from several inches to a few feet across. Larger diseased areas may occur if the affected areas coalesce. Sclerotia (fungal survival structures) are often evident in grass blades. They appear as match-head size or smaller structures, brick red to brown in color, and are embedded in leaf tissue. A magnifying glass or dissecting microscope is useful when looking for these structures.
Many times the injury from light attacks of gray snow mold disappear with higher temperatures and spring growing conditions. In severe cases, however, the grass dies and overseeding will be necessary.
Cultural control practices
- Use a balanced N-P-K fertilizer in the fall and avoid excessive late season applications of water soluble nitrogen. Slow release forms of nitrogen are recommended.
- Continue to mow late into the fall to ensure that snow will not mat a tall canopy.
- Avoid excessive thatch.
- Prevent compaction of snow (such as by snowmobiles) during winter.
- Erect snow fences or other barriers to prevent snow drifts in critical ares, such as gold courses, where snow mold is a problem.
- Lightly fertilize affected turf in the spring to promote growth.
- Overseeding may be necessary if the disease is severe and new growth does not occur.
A late fall application of a fungicide labeled for gray mold control may be necessary in areas with a history of economic damage from snow mold, such as golf courses. Recommended fungicides include Banner, Bayleton, Chipco 26019, Curalan, Daconil, Prostar, Teremec, Thiram, Twosome, and others. Always read and follow label instructions.
This article originally appeared in the March 3, 1995 issue, p. 19.