A healthy, green lawn is a source of pride—but even well-cared-for turf can fall victim to fungus. Lawn diseases thrive in warm, humid conditions or when moisture lingers on the grass. Knowing which fungi you’re dealing with, and how damaging they can be, helps you protect your investment before small patches turn into widespread problems.
Common Types of Lawn Fungus
1. Brown Patch
- Appearance: Large, circular patches of brown or tan grass, often with darker edges.
- Conditions: Thrives in hot, humid weather, especially when nighttime temperatures stay above 68°F.
- Impact: Can kill grass blades quickly but usually spares the crown if treated promptly.
2. Dollar Spot
- Appearance: Small, silver-dollar-sized tan spots that can merge into larger patches.
- Conditions: Common in early summer with cool nights and heavy morning dew.
- Impact: Can spread rapidly across lawns, thinning turf and making it prone to weeds.
3. Pythium Blight
- Appearance: Greasy-looking, water-soaked patches that collapse quickly.
- Conditions: Extremely aggressive in hot, humid weather; often spreads overnight.
- Impact: One of the most destructive fungi—can kill entire sections of turf within days if untreated.
4. Rust Fungus
- Appearance: Grass blades turn yellow-orange and release a powdery rust-colored spore when touched.
- Conditions: Develops in late summer to fall during dry periods with heavy dew.
- Impact: Usually cosmetic but can weaken turf over time.
5. Snow Mold
- Appearance: Matted, gray or pinkish patches visible after snow melts in spring.
- Conditions: Appears where grass was covered by snow for long periods.
- Impact: Pink snow mold can kill grass crowns, while gray snow mold is less severe.
Which Fungi Are Most Damaging?
- High-Risk: Pythium blight and pink snow mold can devastate turf rapidly, requiring immediate treatment.
- Moderate-Risk: Brown patch and dollar spot weaken turf significantly if not addressed but are usually manageable.
- Low-Risk: Rust fungus and gray snow mold are more cosmetic, though repeated infections reduce lawn vigor.
How Fast Should You Treat Lawn Fungus?
The short answer: immediately. Lawn fungi spread quickly under the right conditions, and delays can mean permanent damage.
- Within Days: Pythium blight and brown patch can destroy turf in less than a week.
- Within Weeks: Dollar spot and rust may spread more slowly, but untreated infestations leave thin, weak turf that invites weeds.
- Seasonal Concern: Snow mold requires preventive care in the fall and cleanup in spring to minimize long-term damage.
Preventing and Managing Lawn Fungus
- Water early in the morning to reduce overnight leaf wetness.
- Mow at the correct height and avoid scalping the lawn.
- Improve air circulation by reducing thatch and trimming nearby shrubs.
- Apply fungicides promptly when signs appear—especially for aggressive diseases.
- Fertilize appropriately; both under- and over-fertilization can fuel fungus.
Takeaway:
Some fungi are mostly cosmetic, while others can wipe out large areas of turf in days. The key is early identification and swift action. If you suspect fungus in your lawn, don’t wait—it’s always easier (and cheaper) to treat a small patch than to restore an entire lawn.
