Sod webworms are the reason a South Florida lawn can look fine on Friday and show ragged, brown, scalped-looking patches by Monday. The damage comes from caterpillars less than an inch long that chew grass blades at night and hide in the thatch by day, and the first sign most homeowners notice is not the caterpillar at all. It is the small tan moths that flutter up in a zigzag when you walk across the grass at dusk.
What Sod Webworms Are
The species that does the damage here is the tropical sod webworm. The adult is a dingy tan moth about three quarters of an inch across that rests with its wings folded tight against its body in shrubs and shaded turf during the day. At dusk the moths fly low over the lawn, and the females drop eggs on grass blades as they go. Those eggs hatch in a few days into the larvae that cause the trouble.
The larvae are grayish green with rows of dark spots down the back and a brown head, and they grow to roughly three quarters of an inch before pupating. They feed after dark, chewing the leaf blade down toward the crown, and spend the day curled up in silk-lined tunnels in the thatch layer. A full generation takes about five to six weeks in warm weather, and in South Florida the generations overlap through the warm months, which is why a lawn treated once in July can be chewed up again in September. We treat for sod webworms and armyworms from June through October, which is when we see the heaviest activity in Broward, Miami-Dade, and Palm Beach lawns. Damage often peaks in late summer and early fall, so November is when a lawn that went untreated looks its worst.
Sod webworms feed on all three of the warm-season grasses common in South Florida. St. Augustine takes the most visible hit because of its wide blades, but Bermuda and zoysia lawns are attacked just as readily.
What Sod Webworm Damage Looks Like
The damage is easy to mistake for drought stress, a mower set too low, or chinch bugs, and the wrong diagnosis is the main reason sod webworm problems spread. The signs that point to webworms rather than something else are specific.
- Grass blades with notched, ragged, chewed edges, as if trimmed with dull scissors, rather than yellowing or wilting from the tip down.
- Thin, brown patches that look closely mowed or scalped, often starting in shaded or stressed areas and widening by the day.
- Small green or tan pellets of frass in the thatch at the edge of the damage, and silk webbing visible on dewy mornings.
- Tan moths rising from the lawn at dusk, and birds working the turf during the day, since starlings and other birds pull the larvae out of the thatch.
Chinch bug damage, by comparison, shows up as yellow then straw-colored patches in the hottest, sunniest parts of the lawn, and the blades are sucked dry rather than chewed. Our chinch bug control treatment targets that pest separately. Drought stress recovers quickly after rain or irrigation. Sod webworm damage does not, because the larvae keep feeding.
Sod Webworm vs Armyworm
Armyworms show up in the same season and chew the same way, so the two get confused. Fall armyworms are larger, up to an inch and a half, with light stripes running the length of the body and a pale inverted Y on the dark head. They feed in daylight and move across a lawn in a visible front, stripping it in a matter of days. Sod webworms are smaller, spotted rather than striped, feed at night, and damage spreads in patches rather than a line.
The distinction matters less for the homeowner than for the technician, because both respond to the same curative treatment and both are covered under our lawn insect control service. What matters is confirming that a caterpillar is causing the damage at all before any product goes down.
How We Treat Sod Webworms
Every lawn insect service we run starts with identification. A technician inspects the damaged areas, checks the thatch for larvae and frass, and confirms the pest before choosing a treatment. Sod webworm damage looks enough like drought and chinch bugs that treating on a guess wastes a service call and leaves the real problem growing, so that assessment is not a formality.
Once sod webworms are confirmed, curative treatment targets the larvae where they feed. Because they come out at night and hide in the thatch by day, product placement and timing make the difference between a treatment that works and one that misses them. Our technicians apply the treatment to reach the thatch layer and schedule it so the larvae contact it when they are actively feeding. Lawns with a history of webworm problems are also candidates for preventive treatment during the June through October window, which puts a barrier in the turf before the first generation of the season hatches and avoids the cycle of chewing and recovery that wears a lawn down over a summer.
Treatment stops the feeding, but it does not regrow grass on its own. A lawn that lost blades to sod webworms needs the right recovery conditions, and that is where the rest of our lawn care program comes in. Fertilization gives the surviving crowns the nutrients to push new growth, and irrigation adjustments keep the lawn evenly watered without the overwatering that invites fungus into thinned turf. Where sprinkler coverage is part of the problem, our irrigation and sprinkler maintenance service corrects it.
All products we apply are selected to be safe for kids and pets once dry, which matters on a lawn where both spend their time.
When to Schedule Service
A sod webworm infestation does not burn itself out. Each generation lays eggs for the next, and a lawn that shows chewed patches in early fall will keep losing turf until the larvae are treated or cool weather finally slows them down, which in South Florida can mean December. The sooner the feeding stops, the less resodding the lawn needs on the other side.
If your St. Augustine, zoysia, or Bermuda lawn is showing ragged brown patches, chewed blades, or tan moths at dusk anywhere in Miami-Dade, Palm Beach, or Broward County, schedule a free inspection. We will confirm what is eating the grass, treat it, and set up the recovery plan that brings the lawn back.
