Snow Mold
Microdochium nivale (pink snow mold), Typhula incarnata, T. ishikariensis (gray snow mold)
Overview
Fungal diseases of turfgrass and winter cereals that develop under snow cover or during cool, wet conditions. Appears as circular patches of matted, discolored grass when snow melts. Snow Mold spreads mainly by spores on wind, splash, tools, and crop debris. Humid, crowded plantings and overhead watering favor outbreaks in home gardens and food forests. Causal agent: Microdochium nivale (pink snow mold), Typhula incarnata, T. ishikariensis (gray snow mold). In regenerative gardens, prioritize sanitation, airflow, and unbroken soil cover over calendar spraying, and intervene early when symptoms appear.
Symptoms
Circular patches of matted, bleached, or pinkish-gray grass visible after snow melt. White to pink mycelium on grass blades. Gray snow mold produces small, dark sclerotia. Grass may recover from pink snow mold but gray snow mold kills crowns. Compare several plants and note whether symptoms spread after rain, insect feeding, or wet foliage. Photograph undersides of leaves and cut stems when wilt is present to refine the diagnosis. Rule out simple drought, fertilizer burn, and herbicide drift before assuming a pathogen - abiotic injury often mimics disease.
Environmental Conditions
Cool
Prevention
Avoid late-fall nitrogen fertilization. Mow grass short before winter. Reduce thatch. Improve drainage. Avoid piling snow on turf. Use resistant grass varieties. Mulch to reduce splash, clear season-end debris, and avoid working plants when wet. Design beds for airflow and diverse plantings that support beneficial insects without creating permanent humid pockets around susceptible crops.
Management
Rake matted grass to promote drying and recovery. Apply fungicides in late fall before snow cover in severe areas. Improve air circulation. Overseed damaged areas in spring. Prefer drip irrigation, morning watering, and open spacing so leaves dry quickly. Disinfect pruners between cuts on woody plants. Use copper, sulfur, or biological products only as labeled protectants when pressure is high - they rarely reverse advanced infections alone. Destroy (do not casually compost) highly infectious debris.