How to Prevent Snow Mold in Your Lawn This Winter

What Is Snow Mold?

Snow mold is a fungal disease that develops on lawns under snow cover during winter. It occurs when snow falls on unfrozen ground, creating a moist, insulated environment where fungi thrive. By the time the snow melts in spring, large circular patches of matted, discolored grass become visible.

Two Types of Snow Mold

Gray Snow Mold (Typhula blight)

• Cause: Typhula incarnata and T. ishikariensis fungi
• Appearance: Circular patches of matted, straw-colored grass, 6 inches to 3 feet in diameter
• Damage level: Primarily affects grass blades, not the crown or roots
• Recovery: Usually recovers on its own with spring raking and fertilization

Pink Snow Mold (Microdochium patch)

• Cause: Microdochium nivale fungus
• Appearance: Smaller circular patches (2-8 inches) with pinkish-white fungal growth
• Damage level: More aggressive — can kill crowns and roots
• Recovery: May require reseeding if crowns are killed

Fall Prevention Strategies

1. Mow at the Right Height Before Winter

• Cool-season grasses: Final mowing height should be 2-2.5 inches
• Warm-season grasses: 1.5-2 inches

2. Remove Fallen Leaves

Leaf layers trap moisture and create the same conditions as tall grass — matted organic matter that shelters fungi.

3. Avoid Late-Season Nitrogen

Applying quick-release nitrogen fertilizer too late in fall stimulates succulent new growth that is highly susceptible to snow mold.

4. Improve Drainage

Low spots that collect standing water are prime snow mold locations. Core aeration and topdressing with compost all help water drain away.

5. Fungicide Application (For Severe Cases)

Effective active ingredients: Chlorothalonil, Propiconazole, Fludioxonil, Thiophanate-methyl.

Spring Recovery

1. Rake the affected areas: Gently rake matted grass to loosen it and allow air to reach the soil surface.
2. Apply light nitrogen fertilizer: A quick-release nitrogen fertilizer stimulates recovery.
3. Overseed if needed: If pink snow mold killed the crowns, bare spots will need reseeding.
4. Aerate in fall: If snow mold was severe, core aeration in the following fall improves drainage.

Conclusion

Snow mold is a preventable disease. By keeping your lawn mowed to the correct height, removing leaf debris, avoiding late nitrogen applications, and improving drainage, you can protect your lawn from both gray and pink snow mold.