Snow mold

Pathogen and disease type. The pathogen causing this disease is the fungus Coprinopsis psychromorbida (formerly known as Coprinus psychromorbidus). It is a psychrophilic fungus, meaning it thrives in cold temperatures. This disease is widely recognized as a form of snow mold, affecting plant tissues during winter dormancy and the early spring thaw period.

Host crops. This pathogen has a broad host range, primarily infecting winter cereals such as wheat, rye, and barley. It also causes significant damage to various perennial grasses used for forage or lawns, and in certain conditions, it can affect winter oilseed rape, particularly in regions with prolonged snow cover.

Symptoms and signs. Symptoms typically appear immediately after snowmelt. The infected plants are covered in a dense, white or grayish mycelial mat. The infected leaf tissue becomes water-soaked, collapses, and eventually rots. A distinct diagnostic feature of this fungus is the presence of small black sclerotia, which distinguish it from other snow mold pathogens like Microdochium nivale.

Development and impact. The development of the fungus is favored by persistent snow cover over unfrozen soil, which maintains the high humidity and cool temperatures necessary for the pathogen's spread. The economic impact can be severe, resulting in high plant mortality, thin stands, and the necessity to reseed fields if damage is extensive.

Management and prevention. Controlling Coprinopsis psychromorbida requires a combination of proactive management and chemical intervention:

• Planting resistant crop varieties tailored to the specific climatic zone.
• Implementing crop rotation to minimize the accumulation of pathogens in the soil.
• Applying seed treatments with effective fungicides in the fall to protect seedlings.
• Managing nitrogen application in the autumn to prevent lush, susceptible growth before winter dormancy.
• Improving field drainage to prevent water stagnation after snowmelt.