When there is little or no snow cover, winter wheat can be damaged by environmental stresses, including subfreezing temperatures, standing water, ice encasement, heaving and desiccation. In southern Alberta, warm chinook winds may melt the protective snow cover and cause decreased hardiness of plants and expose them to drying winds and frosts. Some fungi, such as S. borealis, are an endemic disease of wild grasses. Each snow mold has a specific geographic distribution on the prairies and characteristic environmental factors that favor its growth. Snow molds cause the most damage when an early snow storm covers unfrozen soil and snow persists throughout the winter, maintaining high humidity and temperatures of about 0 degrees Celsius at soil level.
Snow molds grow quite actively at temperatures near freezing.
Because of the complexity of the causal factors, the diagnosis of winter damage is difficult when growth resumes in the spring. Damage is often assessed on the basis of symptoms and a knowledge of the terrain, soil conditions, management practices and weather. Desiccation injury often occurs on exposed hills and on bare, wind-swept fields. Damage from snow molds is most prevalent and severe following a long, snowy winter, especially where snow has accumulated in drifts. Damage from snow mold may occur in discrete patches, in large areas, or may cause thinning of the stand within the rows.