Fescue Lawn Diseases: Identification, Prevention, and Control

Healthy cultural practices—proper fertilizing, mowing, and watering—are the best defense against fescue diseases. Fungicides should be a last resort. Here are the four most common fescue diseases in the Southeast.

1. Pythium Blight

When: Late spring (hot days, warm nights, heavy rain).
Symptoms: White fungal growth at edges of dead patches. Worse with excessive seeding, overwatering, or late-spring nitrogen.
Control: Use correct seeding and fertilizer rates. Fungicides are difficult and rarely needed if cultural practices are sound.

2. Brown Patch

When: Summer, when night temps exceed 68°F and heavy nitrogen was applied.
Symptoms: Circular dead patches up to 3+ feet; "doughnut" pattern with green center. Blades brown to crown but crown stays green. White fungal web visible early morning.
Control: Avoid summer nitrogen; water early morning only. Fungicides (chlorothalonil, Bayleton) work but cost ~$100/5,000 sq ft per 14-day application.

3. Slime Mold

Appearance: Looks like oil spilled on the lawn; gray turning black.
Action: Harmless. Wash off with a hose. No fungicide needed.

4. Dollar Spot

When: Cool nights, warm days (spring/fall).
Symptoms: Hand-sized dead spots. Linked to low nitrogen and drought.
Control: Moderate fertilizer + deep weekly irrigation. Fungicides available if needed.

Diagnosing Lawn Problems

Not every brown patch is a disease. Check for: poor drainage (standing water >24 hrs), compacted soil under new sod, or heavy traffic areas (old home plate, goal mouth). If environmental causes are ruled out, submit a 4×4-inch sample (half live, half dead, with roots) to your county Extension office for lab diagnosis (~10 days).

Key Cultural Reminders

• Fertilize fescue only in cool months (fall–spring).
• Water early morning; never early evening.
• Mow 2–3 inches; avoid scalping.
• Brown patch spores are ubiquitous—keep grass strong to resist infection.

Expert Q&A

Q: Can I test soil for fungus?

A: Not practical—every soil contains pathogenic fungi. Strengthen the plant first (fix compaction, seeding rate, watering) before considering fungicides.

Q: Yellow patches in newly seeded fescue—disease?

A: No. Cold temperatures halt photosynthesis. Warm days will green them up.

Q: Can I eliminate brown patch from the soil?

A: No. Spores are always present. Control the environment (water deeply weekly, stop fertilizing after May) to suppress outbreaks.