Sod Webworms: The Moth Behind Chewed, Brown Patches in Summer

That’s tropical sod webworm, the caterpillar stage of a small moth, and it’s one of the late-summer lawn pests that catches New Orleans homeowners off guard. At TurnKey Lawn Care, sod webworm treatment is part of the lawn pest work we do across the metro. If your lawn looks scalped and moths are flying up from it, request a free estimate and we’ll check what’s feeding on it.

This guide covers how to identify sod webworms and their damage, why they hit St. Augustine so hard, how to confirm them, what treatment involves, and how to help the lawn recover without inviting disease.

How to identify sod webworms

What the damage looks like

LSU explains that young larvae chew the edges of leaf blades and leave an uneven appearance, while older larvae chew entire leaves. It also notes that the caterpillars cut grass blades at night, pull them underground and feed on them during the day. The result, according to LSU, is areas that appear scalped and form yellow or brown patches. The damaged grass looks thin and chewed down rather than dried out. The LSU damage article describes how sudden it can seem, noting that the damage often appears to happen overnight. It also points to the notched edges on the grass blades as the telltale sign, along with trails of silky web in the morning dew.

Clue	Sod webworms	Chinch bugs	Fall armyworms
Blades	Notched edges, chewed down	Dry and yellow, not chewed	Skeletonized or eaten to the stem
Other signs	Moths flying up, silky webbing in dew	Insects at the base in a flush test	Striped caterpillars with a Y on the face
Peak season per LSU	July through September	Hot, dry mid-to-late summer	June through November
Look of the patch	Scalped, yellow or brown	Yellow ring around brown center	Sharp edge between damaged and healthy turf

Sod webworms or a mowing problem

Because sod webworm damage looks scalped, it’s easy to blame the mower. A few checks separate the two. Mowing damage usually follows the mower’s path. It shows up in straight strips, on high spots where the deck dipped, or across the whole lawn if the blade was set too low. The cut ends of the blades look torn or frayed if the blade is dull, but the sides of each blade are intact. Sod webworm damage shows up in irregular patches that don’t match the mowing pattern. The blade edges are notched from chewing rather than cleanly cut, and the patches keep spreading between mowings. If you see moths flying up and webbing in the dew, the mower isn’t the cause. Scalping and sod webworms can also happen together. St. Augustine mowed too short is already stressed when the caterpillars arrive, and it has less leaf to recover with. Our page on what happens when you cut grass too short explains why height matters so much in summer.

Why St. Augustine takes the worst of it

LSU lists St. Augustine, Bermuda and centipede among the grasses tropical sod webworms commonly target. In practice, St. Augustine often looks worst. The LSU damage article describes St. Augustine lawns being hit severely, and it notes seeing St. Augustine completely devastated growing next to zoysia that was totally unaffected. It describes Bermuda and centipede showing less damage. Because St. Augustine is the grass most New Orleans yards are built on, late summer is a time to keep an eye out. If you’re choosing grass for a new area and sod webworms have been a repeat problem in your yard, note that the LSU article saw zoysia come through untouched beside a stripped St. Augustine lawn. Our St. Augustine grass care guide covers the everyday care that keeps it strong through the season.

How to confirm sod webworms

The soap flush brings the caterpillars up from the base of the grass so you can see them. It’s the same test used for other lawn insects.

1. Mix the solution. LSU uses 1 tablespoon of lemon-scented dish soap in 1 gallon of water.
2. Pour at the edge of the damage. Target the healthy-looking grass beside the scalped area, where caterpillars are actively feeding.
3. Watch for five to ten minutes. Look for small green caterpillars crawling up out of the grass.
4. Check early in the morning. The caterpillars feed at night, and the webbing is easiest to see while dew is still on the lawn.
5. Note what else you see. Moths flying up and notched blades together make the diagnosis much clearer.

Our guide to grub and lawn pest control covers the other quick checks for insect damage in New Orleans lawns.

What treatment involves

LSU recommends applying insecticide when tropical sod webworm injury is excessive or large numbers of larvae are found during the flush test. The LSU damage article notes that control is possible and that the same insecticides that kill armyworms work well on tropical sod webworms. Product choice, rate and any watering-in instructions come from the label, which has to be followed exactly. Treating the active edge of the damage and the grass just beyond it matters, because the caterpillars are moving outward. Late in the season, the question of whether to treat depends on how much damage is still being done. If moths are still flying and the flush test brings up caterpillars, treatment can protect the rest of the lawn going into fall. We handle sod webworm treatment as part of our lawn pest control, alongside the care changes that help the lawn recover.

Helping the lawn recover without inviting disease

Recovery is where many homeowners go wrong. The instinct after damage is to fertilize heavily to push the grass back, and in late summer that can create a new problem. The LSU damage article recommends raising the mowing height to about three inches and maintaining adequate soil moisture. It advises avoiding nitrogen fertilizer after mid-August, because doing so may lead to increased brown patch disease. A recovery plan for late summer and early fall:

• Raise the mower on St. Augustine to about three inches and leave it there
• Water deeply in the early morning to keep soil moisture adequate, without watering at night
• Hold off on nitrogen after mid-August and save feeding for when the lawn is actively growing next spring
• Flush-test again a week or two later, since the injury season runs into October
• Repair areas that stay bare into spring with plugs or sod

Our post on brown patch fungus in New Orleans lawns explains why late-season nitrogen and fall weather are such a risky combination.

Keep an eye out next summer

Sod webworms tend to come back when conditions suit them. LSU’s seasonal chart shows injury possible from May through October and most common from July through September. A few simple habits make the next outbreak easier to catch early:

• Notice when moths start flying up from the lawn in early summer
• Look at the blade edges along any patch that suddenly looks shorter than the rest
• Walk the lawn in the morning dew and look for silky webbing
• Run a flush test at the first sign rather than waiting for a large scalped area

Frequently asked questions