Diagnosing Brown Patches in St. Augustine Grass: Chinch Bugs vs. Fungal Diseases

Brown patches in St. Augustine grass during drought are alarming, but the coffee can test you performed—floating a can in the soil to flush out chinch bugs—came up empty. That's a strong clue: it's probably not chinch bugs.

When It's Not Chinch Bugs

Several fungal diseases mimic chinch bug damage: brown patch, gray leaf spot, and take-all root rot. These thrive in lawns heavily maintained with synthetic fertilizers, herbicides, and fungicides—chemicals that wipe out beneficial microbes and leave the door open for pathogens.

Drought Complicates Diagnosis

Drought stress causes yellowing and browning that looks identical to disease. The grass may simply be dormant. Wait for rain or irrigate deeply once, then observe recovery patterns.

Next Steps

1. Stop all chemical applications. Let soil biology recover.
2. Water deeply once per week (if no rain) in the early morning.
3. Mow high (3.5–4 inches) to shade soil and reduce stress.
4. Submit a sample to your local extension service for lab diagnosis if patches persist after rain returns.

Healthy soil grows resilient grass. Chemicals create dependency; biology creates resilience.