Snow mold

Sclerotinia borealis is a pathogenic fungus that causes a destructive disease known as snow mold, primarily affecting winter cereals and perennial grasses. It is particularly prevalent in regions with cold climates and prolonged snow cover, where the pathogen thrives at temperatures just above freezing.

The disease poses a significant threat to winter wheat, winter rye, and various forage grasses. By attacking plants during the dormancy period, Sclerotinia borealis can cause severe thinning of crop stands, which leads to reduced yields and, in extreme cases, total failure of the winter crop area, requiring replanting in the spring.

Initial symptoms are characterized by the appearance of a gray or white mycelial mat on leaves and stems as the snow melts. Over time, the affected plant tissues turn brown and die. The formation of hard, black sclerotia—the resting structures of the fungus—on the surface of the infected tissue is a hallmark of the pathogen's presence and ensures its long-term survival in the soil.

The development and spread of the disease are heavily dependent on environmental conditions. A thick and persistent snow cover is essential, as it insulates the soil surface, keeping it at a temperature range where the fungus remains active. High humidity levels during the spring thaw further facilitate the rapid infection of healthy plants by the spreading mycelium.

Effective management requires an integrated approach to mitigate the impact of the disease. Key strategies include:

• selecting cultivars that show documented resistance to cold-weather fungal pathogens;
• treating seeds with systemic fungicides to protect seedlings during the critical initial growth stages;
• avoiding excessive nitrogen fertilization in the late autumn to prevent succulent, susceptible plant growth;
• implementing proper crop rotation to break the cycle of the fungus in the soil;
• ensuring field drainage to prevent excess moisture accumulation during late winter.