Zoysiagrass Diseases: Brown Patch, Dollar Spot, Rust, and Diagnosis

Prevention First

Proper fertilization, mowing, and watering beat fungicides for disease control.

Three Common Diseases

Brown Patch

Heavy fertilization + nights >68°F, days >80°F. Patches merge >3 ft, sometimes "doughnut" pattern. Control: moderate summer fertilization, early morning irrigation, labeled fungicides.

Dollar Spot

Cool nights, warm days in spring/fall. Hand-sized dead spots, lesions on blade edges, straw-colored tips. Associated with low fertility and drought. Control: moderate fertilizer, deep weekly irrigation, labeled fungicides.

Rust

Orange powder clouds when mowing in late fall. Favors cool, moist, shady conditions. Control: moderate fertilizer, low-N fall fertilizer (5 lbs 5-10-15/1,000 sq ft), mow every 4–5 days, catch clippings, labeled fungicides.

Is It Really Brown Patch? Environmental Mimics

• Poor drainage/standing water → root rot
• New sod on unplowed compacted soil → poor rooting
• High-traffic areas (home plate, goal) → concrete-hard soil

True Brown Patch Symptoms

• Small spots enlarge rapidly in warm weather
• "Doughnut" appearance: tan ring with green center
• Blades brown to crown, but crown stays green
• White fungal web at patch edge on hot, damp mornings

Keeping Grass Healthy

Fungus is always present; grass gets sick when weak. Fertilize appropriately (cool months for fescue, warm for Bermuda).

Watering to Reduce Disease

• Never early evening.
• Best: early morning after dew dries.
• Alternative: night watering (grass already wet with dew).
• Brown patch needs 14–16 hrs wet leaf surface to reproduce.

Fungicide Reality Check

Effective but costly: ~$20/1,000 sq ft per application, every 14 days. For 5,000 sq ft = $100 every two weeks.

Positive Identification

Submit sample (4×4 inch, half live/half dead, with roots) to county Extension office for free lab diagnosis. Results in ~10 days.

Case Study: Winter Kill in One Spot

Q: Emerald zoysia dies in same sunny spot each winter. What to do?
A: Check for compacted or soggy soil. Dig 6 inches, add manure, re-sod. Ensure water doesn't accumulate—redesign drainage if needed. Oxygen limitation is the root cause.