Texas Turf Pros • Updated July 2026 • 6 min read

Brown Patch in St. Augustine: How to Identify It, Treat It, and Stop It Coming Back

Every fall, like clockwork: brown circles bloom in St. Augustine lawns across Marble Falls, Horseshoe Bay, and Kingsland — especially under the oaks. That’s brown patch (technically large patch, Rhizoctonia), and it is the most common lawn disease in the Hill Country.

How to recognize it

• Circular or irregular brown patches, from dinner-plate size to several feet across, that expand outward — often with a yellowish “smoke ring” at the growing edge.
• The pull test: grass blades at the edge of the patch pull free with almost no effort, and the base of the blade is rotted brown while the roots stay intact. That rotted leaf base is the fingerprint — grub damage lifts like carpet (roots eaten), drought turns whole areas uniformly tan, but only brown patch rots the blade base.
• Timing: it fires when nights cool into the 50s–60s°F and moisture lingers — October/November, and again as lawns green up in spring.

Why your lawn, why fall

The fungus is present in virtually all St. Augustine lawns year-round, waiting for its conditions: cool nights + wet leaves + lush growth. The Hill Country recipe that feeds it:

• Evening irrigation. Watering at 7pm keeps leaf blades wet for 12+ hours — a fungal incubator. Water pre-dawn instead.
• Shade. St. Augustine under live oaks dries slowly and stays humid at the canopy level.
• Late-season nitrogen. A heavy feeding in October pushes soft, lush growth that brown patch devours. Fall fertilization needs the right formulation, not the summer one.
• Thatch and compaction hold moisture at the crown, right where the fungus attacks.

Treating an active outbreak

Correctly timed fungicide applications stop active brown patch and protect the surrounding turf — product choice, rate, and interval matter, which is why this is licensed-applicator work. The patches themselves recover as the grass regrows; expect scars to fill in over weeks, faster in spring.

What doesn’t work: more water (feeds it), more fertilizer (feeds it), or waiting (it expands until conditions change).

Prevention is the professional move

On a golf course, turf disease is managed before symptoms — preventive applications go down when conditions align, because visible damage on a fairway is already a failure. Chronic lawns get the same treatment here: for a St. Augustine lawn that browns out every fall, a preventive fungicide in early fall (and sometimes at spring green-up) costs less than the cure and keeps the lawn whole.

The rest of prevention is cultural, and it’s all schedule discipline: water before dawn, feed the right analysis at the right time, and keep the lawn thick enough to dry fast. A yellowing, struggling lawn also gets hit harder — if yours runs yellow on caliche soil, see our guide to iron chlorosis on Hill Country soil.

Quick answers

Will brown patch kill my St. Augustine?

Large patch usually rots leaf blades, not roots, so lawns typically recover once it's treated — but severe, repeated outbreaks thin the turf and open the door to weeds. Chronic lawns should be on preventive treatment.

Can I treat brown patch myself with a store fungicide?

Store products can suppress mild cases, but rate, coverage, and reapplication interval are where DIY treatments usually fail — and misdiagnosis is common (grubs and chinch bugs get sprayed with fungicide constantly). A correct on-site diagnosis is worth more than any product.

Should I stop watering if I see brown patch?

Don't stop — shift. The lawn still needs water, but it needs it before dawn so blades dry by mid-morning. Evening watering is the single biggest brown patch accelerant in home lawns.