Five different lawn problems all look like "brown spots," and each one needs a different fix. Guess wrong and you waste money, or make it worse.
- Brown patch
- Take-all root rot
- Chinch bugs
- Gray leaf spot
- Sod webworms
Before you buy anything, do three quick tests. Together they take about ten minutes and tell you which problem you actually have. Then jump to the fix.
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What season is it?
The calendar narrows it down fast. Here's what usually shows up when in Houston.
Spring
Take-all root rot shows up most. Brown patch and large patch hang on while nights are cool and wet.
Summer
Chinch bugs in hot, sunny spots. Gray leaf spot in humid weather. Plain heat stress.
Late summer
Sod webworms and fall armyworms, often right after a rain.
Fall & winter
Brown patch and large patch return with cool, wet weather. Take-all gets started.
The 5 brown-spot problems at a glance
Plus the two look-alikes people mix them up with.
| Problem | Type | Key sign | Test | When | Fix |
|---|---|---|---|---|---|
| Brown patch & large patch | Fungus | Rings or circles, darker edge | Tug: blades slip out | Cool, wet: spring & fall | Shop → |
| Take-all root rot | Fungus | Irregular yellow thinning | Tug: runner lifts, roots black | Spring, after a wet winter | Shop → |
| Chinch bugs | Insect | Sunny spots near concrete | Soap test | Summer | Shop → |
| Gray leaf spot | Fungus | Gray-tan spots, dark edges | Blade: spots, not bites | Hot, humid summer | Shop → |
| Sod webworms & armyworms | Insect | Chewed, ragged blades | Blade: bites | Late summer & fall | Shop → |
| Look-alike: grubs | Insect | Turf lifts like carpet | Tug: roots chewed off | Any season | Shop → |
| Look-alike: low iron | Nutrient | Yellow with green veins | None. It's yellow, not brown | Spring & summer | Shop → |
The Tug Test
Go to the edge of a brown spot, where brown meets green. That's where the problem is still active.
- Grab a few blades between your thumb and finger.
- Pull gently, the way you'd test a loose tooth.
- Then grab a runner (the stem along the ground) and lift.
↓ Photos: what brown patch looks like · what take-all root rot looks like
05 Tug Test for Brown Patch
05 Tug Test for Take all Root Rot
Look at the Blade
Pick a few blades from the edge of the damage and look closely, in good light. Reading glasses help.
↓ Photos: sod webworm damage · gray leaf spot
06 Blade Sod webworm damage, chewed brown grass next to green
06 Blade Gray leaf spot on a St. Augustine blade
The Soap Test
Suspect chinch bugs when a sunny patch near the driveway, sidewalk or street keeps spreading even though you water it.
- Part the grass at the edge of the damage and look at the soil line for tiny black-and-white bugs.
- Mix about 2 tablespoons of dish soap in a gallon of water.
- Pour it slowly over a 3-by-3-foot area at the edge of the damage.
- Wait a few minutes and watch the grass surface.
↓ Photo: chinch bug damage
07 Soap Test Chinch bug damage in a sunny Houston lawn
Here's how to fix it
Three rules first: treat one problem at a time, fix your watering before you buy anything, and always follow the product label.
Brown patch & large patch
Water only early in the morning, so blades dry by midday. Hold off on nitrogen while the weather is cool and wet. Apply a lawn fungicide at the first sign and repeat as the label says.
Take-all root rot
Fix drainage and cut back on water. Top-dress with a thin layer of peat moss to lower the soil pH, and use a fungicide labeled for take-all. Expect recovery to take a season or more.
Chinch bugs
Treat the damaged area plus a few feet into the green grass around it with a product labeled for chinch bugs. Water as the label says, then recheck in two weeks.
Sod webworms & fall armyworms
Treat late in the day, when the caterpillars feed. Act fast with armyworms, because they can strip a lawn in a few days. The grass usually grows back once they're gone.
Gray leaf spot
Stop summer nitrogen, water in the morning, and don't mow wet grass. Use a fungicide labeled for gray leaf spot, and keep the mower blade sharp.
Grubs
Dig up a square foot. If you count more than about 5 to 10 white C-shaped grubs, treat with a grub control and water it in.
Not brown, just yellow?
If the grass is yellow with green veins, especially right after you fed it, it's usually iron. Our alkaline Houston soil locks it up. A chelated liquid iron greens it up in about a week.
Six habits that stop brown spots
Water deep, not often
About 1 inch a week in summer, rain included, in one or two waterings.
Watering guide →Water between 4 and 9 AM
Wet grass at night feeds fungus. Morning water dries by midday.
Water smarter store →Mow at 3–4 inches
Taller St. Augustine shades the soil and holds up to heat. Keep the blade sharp.
Feed by the soil, not the calendar
Too much nitrogen at the wrong time invites brown patch and gray leaf spot.
Texas Two-Step →Fix drainage & thatch
Soggy, compacted soil is where take-all and brown patch start.
Soil improvement →Scout the edges in July & August
Check sunny spots near concrete every week or two. Catch chinch bugs early.
Quick answers
What causes brown spots in a Houston St. Augustine lawn in summer?
In summer the usual causes are chinch bugs in hot, sunny spots near concrete, gray leaf spot in humid weather, sod webworms late in the season, and plain heat or water stress. The tug, blade and soap tests tell them apart in about ten minutes.
How can I tell a lawn fungus from bugs?
Look at the blades. Chewed or ragged blades mean insects. Blades with spots, or blades that slip out of the runner when you tug, point to a fungus.
How do I control brown patch?
Brown patch and large patch thrive in cool, wet weather in spring and fall. Water only early in the morning, skip nitrogen during those months, improve drainage, and apply a lawn fungicide at the first sign, repeating as the label directs.
Can my lawn recover from take-all root rot?
Yes, but slowly. Improve drainage, cut back on water, top-dress with a thin layer of peat moss and use a fungicide labeled for take-all. Expect a season or more before the grass fills back in.
Why is my lawn yellow after I fertilized it?
Usually it's iron, not nitrogen. Houston's alkaline soil locks up iron, so grass turns yellow with green veins. A chelated liquid iron typically greens it up within about a week.
Should I use weed-and-feed on a lawn with brown spots?
No. Weed-and-feed puts down fertilizer and weed killer at the same time, and the timing is wrong for both. It can stress grass that is already struggling. Fix the brown spots first, then treat weeds separately.
How often should I water my St. Augustine?
About an inch a week in summer, rain included, applied in one or two deep waterings between 4 and 9 in the morning. Water less in spring and fall.
What if my lawn has more than one problem?
It happens, especially in late summer. Treat the most active problem first, usually insects, then the fungus, and fix watering underneath it all. If you're not sure, send Todd photos.
Let us take a look
Send Todd a few photos and he'll tell you what he'd do. It's free. For the fastest answer, include:
- One wide photo and one close-up of the edge
- Your grass type, if you know it
- How often and when you water
- How much sun the spot gets
More help: Houston Lawn Care Guide · Free weekly magazine
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