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Brown Patch in St. Augustine Lawns: A Houston Fall Guide

Every October, Houston lawns that looked fine all summer start growing brown rings. If yours is St. Augustine, the most likely cause is the fungal disease most people call brown patch. In St. Augustine, Texas A&M AgriLife's turf specialists call it large patch, and the difference in name matters less than the timing: it shows up when nights cool off and the grass stays wet.

This guide covers what brown patch in St. Augustine looks like, why fall brings it, how to tell it apart from chinch bugs or a dry spot, and the watering and mowing changes that actually help.

What brown patch looks like in a Houston St. Augustine lawn

Texas A&M AgriLife Extension's publication on large patch in warm-season turfgrass (E-633) describes the signs plainly:

Circular, discolored patches in the lawn.
An orange or yellow outer edge. Those orange blades at the border are the newly infected grass.
Blades that pull out easily. Tug on a brown shoot at the edge of a patch. If it slides out of its sheath where it joins the runner, that's the field test AgriLife describes for this disease.
Dark brown lesions on the stems and sheaths, low down near the soil.

The leaves themselves stay on the plant and rot in place. That's one of the clearest ways to tell it from insect damage, which we'll come back to.

On the name: the same fungus, Rhizoctonia solani, causes "brown patch" in cool-season grasses up north. In St. Augustine and zoysia, AgriLife calls it large patch and notes it is the most chronic and economically important disease of both grasses in Texas. Most Houston homeowners, garden centers and lawn companies still say brown patch, and they're all talking about the same rings.

Why it shows up in fall: cool nights, wet grass

The fungus lives in the soil and thatch year-round. It survives a Houston summer, but it doesn't do much damage in the heat. According to AgriLife, the disease occurs when temperatures drop below 70°F and thrives in cooler weather when the soil is wet. That's why it appears in spring and fall.

In Houston, fall is the bigger risk. The first real cold fronts of October bring cool nights while the ground is often still wet from rain or from a sprinkler schedule that was set for August. A 2018 AgriLife report on a cool, record-wet September described exactly that combination as "perfect conditions" for the disease.

AgriLife's E-633 lists the conditions that make it worse:

Over-fertilizing late in the fall
Poor drainage
Over-irrigation
Mowing too low
Too much thatch

Several of those are common in Houston yards. Much of the area sits on heavy clay that holds water, and plenty of sprinkler systems are still running a summer schedule in October. Shady spots under big trees stay wet longer after rain, too.

Brown patch vs. chinch bugs vs. drought stress

Brown rings in St. Augustine can come from at least three different problems, and the fix for one can make another worse. Here's how to sort them.

Brown patch (large patch)

When: Fall and spring, with cool nights and wet soil.
Shape: Roughly circular rings, often with an orange or yellow edge.
The test: Blades at the edge pull easily out of the sheath. Leaves rot on the plant.
Where: Often in low spots, shady areas, or zones that get too much water.

Chinch bugs

Chinch bugs are a hot, dry-weather pest. AgriLife's 2018 report noted that cool, wet fall conditions are too wet and cool to support chinch bug populations. If your brown area appeared in July in the sunniest, hottest part of the yard, near the driveway or sidewalk, think chinch bugs. If it appeared in October after a rainy week, brown patch is the better guess.

Drought stress or a sprinkler miss

A dry spot usually follows the pattern of your sprinkler coverage, not a circle: the corner a head doesn't reach, the strip by the curb, the area behind a broken nozzle. The grass looks gray-green or straw-colored and wilted, but the blades don't pull loose from the runners. If an irrigation check finds a broken or blocked head, you've found your answer.

Fall armyworms

The same 2018 AgriLife report points to one more look-alike: fall armyworms. They eat the grass blades, so the lawn looks chewed and ragged. Brown patch leaves the blades intact while they rot.

If you can't tell, don't guess with a product. AgriLife's advice is that diagnosis by a certified nursery professional or turfgrass specialist is the most accurate route. Your county AgriLife Extension office is a good place to start.

Watering and mowing changes that help

AgriLife's E-633 is clear that large patch is hard to get rid of once it's established, and it tends to come back under the same conditions. Prevention is mostly about changing the conditions. Their list of cultural practices:

Water early in the morning, so the grass dries during the day instead of staying wet overnight.
Water evenly and only when needed. In a cool, rainy October, that may mean turning the sprinklers off for a while. The 2018 report's first recommendation was simply to shut off irrigation.
Fix drainage in spots that hold water or stay saturated.
Mow at the right height. AgriLife gives 2 to 3 inches for St. Augustine. Scalping it lower stresses the grass.
Avoid mowing wet grass, which spreads the problem around.
Reduce thatch through core aeration and raking.
Balance the nitrogen. AgriLife's guidance is to fertilize about six weeks before the first frost and three weeks after spring green-up, and not to keep pushing nitrogen late into the fall.
Thin out shade where you can. Lower limbs that keep a patch of lawn wet and dark are worth a look. Our guide on when to trim oak trees in Houston covers the timing for live oaks.

The good news, also from AgriLife: lightly affected grass usually recovers as temperatures rise in late spring, and new growth fills in over the summer. Where the disease has killed crowns and roots, the area may need new sod.

What about fungicide?

Fungicides are an option, but timing is everything. AgriLife says the best protection comes from applying before symptoms appear, when soil temperatures drop below 70°F in the fall, and that efficacy is limited once the disease is already showing. Spring applications are not cost-effective, according to the same publication.

If you go that route, use a product labeled for large patch or brown patch on St. Augustine and follow the label exactly. Some fungicides on the market are not approved for home lawns at all. This is one reason many homeowners hand this job to a lawn care company.

When to call a lawn care company

You can handle most of this yourself: adjust the sprinklers, raise the mower, stop fertilizing, and wait for spring. A professional is worth calling when:

You're not sure what you're looking at. A lawn care company sees brown patch, chinch bugs and dry spots every week and can usually tell them apart on sight.
It comes back every fall in the same spots. That usually points to drainage, thatch or a watering problem that needs fixing rather than treating.
You want a preventive program with fungicide applied at the right time, by someone using products labeled for residential lawns.
Large areas have died and you're weighing resod against waiting.

When you call, ask what they think the cause is and how they'll confirm it. A good answer mentions the season, the pattern of the damage and your watering. If the sprinkler schedule is part of the problem, an irrigation company can reset the controller and fix coverage at the same time.

FAQ

Will brown patch kill my St. Augustine grass?

Light cases usually recover as temperatures rise in late spring, according to Texas A&M AgriLife. Severe cases that damage crowns and roots may need resodding.

Should I water more to help the brown spots?

Usually not. Brown patch is driven by cool temperatures and wet grass, so extra water tends to make it worse. Water early in the morning and only when the lawn needs it.

Is brown patch the same as large patch?

In St. Augustine, yes for practical purposes. AgriLife uses "large patch" for the warm-season grass version of the disease. Most people in Houston still call it brown patch.

Should I fertilize to green the lawn back up?

Not in late fall. Late-fall nitrogen is one of the conditions AgriLife lists as favoring the disease.

Find help

Browse lawn care companies in the Houston area in our directory. Listings marked ✓ Verified have been confirmed directly with the business.

Sources: Texas A&M AgriLife Extension, E-633, How to Diagnose and Manage Large Patch Disease in Warm-Season Turfgrass; AgriLife Today, September 27, 2018. This guide is general information, not a treatment plan for your lawn.