Cold-Weather Fungal Pathogens: ID and Control

By James Wilson · October 12, 2026

Cold-Adapted Fungi: A Unique Pathogen Group

While most plant pathogenic fungi thrive in warm, humid conditions (75-85°F), a significant group has evolved to exploit cool-season environments. These psychrotolerant and psychrophilic fungi can grow at temperatures as low as 32°F (0°C), making them active during fall, winter, and early spring when most other pathogens are dormant.

Major Cold-Weather Fungal Genera

Microdochium nivale (Pink Snow Mold)

One of the most cold-adapted plant pathogens known. Active at 32-50°F, it causes circular patches of matted, pink-tinged grass under snow cover. Common on lawns that receive heavy snow without dormancy preparation. Control: avoid late-fall nitrogen fertilization, mow grass short before winter, and apply potassium-rich fertilizer in fall to promote cold hardiness.

Sclerotinia (White Mold)

Produces hard, black sclerotia that survive freezing temperatures for years. Active at 40-65°F with high humidity. Attacks over 400 plant species, causing water-soaked lesions and white, cottony mycelium. In gardens, most common on lettuce, beans, and brassicas grown in cool seasons. Remove and destroy all infected plant material — sclerotia persist in soil for 5+ years.

Typhula (Gray Snow Mold)

Produces distinctive tan-to-gray sclerotia (small, hard structures) visible on infected leaves. Active under snow cover at near-freezing temperatures. Damage appears as circular gray patches when snow melts. Less destructive than pink snow mold — lawns typically recover without treatment.

Diagnosis Framework

Cold-weather fungal diseases share common diagnostic features:

Active during cool, wet periods (fall, winter, early spring)
Circular or spreading patches (not random scattered damage)
Visible mycelium under humid conditions
Presence of sclerotia or other survival structures
Damage visible after snow melt or cold rain events

Integrated Management

Combine cultural controls (proper fall cleanup, drainage improvement, resistant varieties), biological controls (Trichoderma harzianum applications in fall), and chemical controls (copper-based fungicides for organic gardens, applied before infection periods) for the most effective management strategy.