Brown patch is the most common fungal disease affecting warm-season grasses in North Texas. It strikes with particular force during the humid months of May through September, when Dallas regularly experiences overnight humidity above 80% combined with daytime temperatures exceeding 90°F. If you've noticed circular brown patches in your St. Augustine, Zoysia, or Bermuda lawn that seem to expand outward like a target ring, brown patch is almost certainly the cause.
What Causes Brown Patch?
Brown patch is caused by the fungus Rhizoctonia solani, which lives naturally in soil and plant debris. Under favorable conditions — warm nights (75–95°F), high humidity, poor air circulation, and excess nitrogen — the fungus produces aggressive hyphae that kill grass blades, stolons, and rhizomes.
The disease is most severe on:
- St. Augustine grass — most susceptible, especially 'Floratam' and 'Ramatura' cultivars
- Zoysia grass — moderate susceptibility, particularly in shaded areas
- Bermuda grass — least susceptible but vulnerable when over-fertilized
- Tall fescue — can be affected in transition zones during spring/fall
Identifying Brown Patch vs. Other Problems
Classic Symptoms
- Circular patches 1–10 feet in diameter with dark brown centers
- Distinct "smoke ring" border of tan-brown dead grass surrounding the center
- Blades appear water-soaked before turning brown
- Patches often appear in low-lying or poorly drained areas
- Morning: patches may look green (grass recovers slightly); by afternoon they turn brown again
Distinguishing from Similar Problems
| Problem | Key Difference |
|---|---|
| Drought stress | Uniform yellowing, no defined circular pattern |
| Chinch bug damage | Straw-colored (not brown), found in sunniest spots, float test positive |
| Take-all patch | Smaller circles (6–18 inches), more common in fall/spring |
| Pythium blight | Cottony white fungal growth visible at dawn, faster spread |
Treatment Protocol
Immediate Fungicide Application
For active infections, apply a systemic fungicide containing one of these active ingredients:
- Azoxystrobin (e.g., Heritage) — protectant + curative, 14–21 day interval
- Propiconazole (e.g., Banner Maxx) — systemic, 21–28 day interval
- Myclobutanil (e.g., Eagle) — effective on severe cases, 14-day interval
- Chlorothalonil (e.g., Daconil) — contact fungicide for mild cases
Application tips:
- Treat the entire affected area plus a 5-foot buffer zone
- Apply in the early morning when leaves are still wet with dew (improves coverage)
- Use enough water to wet the thatch layer thoroughly (0.1–0.2 inches)
- Rotate fungicide classes between applications to prevent resistance
- Two applications at 14-day intervals typically control active infections
Cultural Practices to Prevent Recurrence
- Reduce evening irrigation: Water in the early morning (before 6 AM) so foliage dries before nightfall
- Improve air circulation: Prune overhanging branches, remove dense shrubs near the lawn
- Avoid excess nitrogen: Use slow-release fertilizers; skip applications during peak humidity months
- Mow at proper height: St. Augustine at 3.5–4 inches, Zoysia at 1.5–2.5 inches — never stress the grass by cutting too short
- Aerate annually: Core aeration in late spring improves drainage and reduces thatch buildup
- Rake out thatch: Keep thatch below 0.5 inches — thick thatch holds moisture against the crown
Seasonal Prevention Calendar for Dallas
- April: Apply preventive fungicide if brown patch occurred the previous year
- May–June: Monitor weekly; apply first treatment at first sign of symptoms
- July–August: Peak risk period. Maintain strict irrigation schedule, avoid nitrogen
- September: Final treatment window; reduce water as temperatures drop
- October: Brown patch typically resolves as nights cool below 70°F
Fighting a Lawn Disease?
Our team diagnoses and treats fungal infections with professional-grade products and proper application equipment. One visit can save your lawn from months of recurring damage.
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