Sod Webworms in Florida Lawns: Signs and How to Stop Them

If patches of your St. Augustine lawn suddenly look thin, chewed, and ragged in late summer, you may be dealing with one of the most common turf pests we see across Central Florida. Sod webworms in Florida lawns can go from invisible to obvious in a matter of days, and homeowners around Orange City, DeLand, Sanford, and the greater Orlando metro often mistake the damage for drought or fungus. The good news: once you know what to look for, sod webworms are very manageable, and a healthy lawn usually bounces right back.

Here’s how to recognize them, confirm you actually have them, and stop them without overreacting or dumping unnecessary chemicals on your yard.

Why These Caterpillars Thrive in Central Florida

The pest most of us deal with locally is the tropical sod webworm (Herpetogramma phaeopteralis) — the larval (caterpillar) stage of a small, dull-brown moth. The moths themselves don’t damage your grass; they just lay eggs. It’s the tiny green-to-tan caterpillars that hide in the thatch by day and feed on grass blades at night.

Our zone 9b climate is practically a buffet for them. The hot, humid summers and heavy June-through-September rains give them ideal breeding conditions, and our long warm season means multiple overlapping generations from roughly late spring well into fall. Because each generation can complete its cycle in just a few weeks during peak heat, damage that looks minor one weekend can be widespread the next. St. Augustine, the dominant turf in this region, is a favorite, though they’ll happily chew Bermuda, zoysia, and bahia too.

Why people miss them at first

• Early damage looks like notched or “see-through” blades rather than dead patches, so it reads as harmless wear.
• The damage often shows up in the same stressed, sunny, or recently fertilized areas where people assume it’s a watering problem.
• By the time thinning is obvious, an overlapping second generation may already be feeding.

Signs You Have Sod Webworms

Catching sod webworms in Florida turf early makes treatment far easier, so it pays to know the tells. Walk your lawn and look for these:

• Ragged, notched grass blades. The earliest sign — blades look chewed along the edges or have transparent “windowpane” patches where the caterpillar scraped the surface.
• Thinning, irregular patches. As feeding increases, you’ll see uneven thin spots that can spread quickly, often looking like the lawn was scalped low.
• Green pellets (frass). Tiny green or tan droppings down in the thatch are a dead giveaway.
• Small moths flushing up. When you walk across the lawn or mow at dusk, dull tan moths flutter up a few feet and resettle.
• Birds working the lawn. Lots of birds pecking your turf are often feasting on caterpillars.

The soap test: confirm before you treat

Never spray blind. Mix about two tablespoons of dish soap into a gallon of water and drench a two-foot-square section at the edge of a damaged area. Within a few minutes, any caterpillars present will wriggle up to the surface to escape the irritation. As a rule of thumb, UF/IFAS and lawn-care guidance treat roughly 10 to 15 caterpillars per square yard as the point where control is warranted. A two-foot square is about four square feet, so that threshold works out to roughly four to seven caterpillars surfacing in your test patch — if you turn up more than a handful in that spot, you’re at the action threshold and can treat with confidence.

How to Stop Sod Webworms

You have good options, from gentle to conventional. Start with the least aggressive approach that fits the severity.

Biological and lower-impact controls

• Bt (Bacillus thuringiensis). A naturally occurring bacterium that targets caterpillars specifically and is easy on beneficial insects. Best on younger larvae and applied in the evening, since sunlight breaks it down.
• Spinosad. Derived from a soil organism, effective on sod webworms, and gentler on many beneficials than older chemistries. Also best applied late in the day.

Conventional insecticides

For heavier infestations, products containing bifenthrin or other labeled pyrethroids work well. Whatever you choose, apply in the late afternoon or evening when the caterpillars come up to feed, and water it in only as the label directs. Always follow the label — it’s the law, and it’s also how you avoid wasting product or harming pollinators.

A few practical pointers

• Mow before treating so the product reaches the thatch where larvae hide.
• Hold off on heavy irrigation right after a foliar treatment so it isn’t washed away.
• Don’t over-fertilize with quick-release nitrogen — lush, fast growth tends to attract more egg-laying moths.

Helping the Lawn Recover

Here’s the reassuring part: sod webworms rarely kill an established St. Augustine lawn. They chew the blades but generally leave the runners and roots intact, so once the feeding stops, the turf regrows. Support that recovery with proper watering (deep and infrequent, in the early morning), a balanced feeding once growth resumes, and a sharp mower blade at the right height. A vigorous lawn shrugs off webworm damage far better than a stressed one.

Frequently asked questions

When is sod webworm season in Central Florida? Activity ramps up in the warm, wet months and typically peaks from mid-summer into fall, though our long season can stretch it.

Will my lawn die from sod webworms? Usually not. They damage blades, not roots, so an established lawn typically recovers once they’re controlled.

Do I need to treat the whole yard? Often you can spot-treat the active areas, especially if you catch them early with the soap test.

How fast do they spread? Quickly — damage can expand noticeably within days in peak season, which is why early detection matters.

Want a Second Opinion on Your Lawn?

If your turf is thinning and you’re not sure whether it’s sod webworms, drought, or disease, we’re glad to take a look. Misdiagnosing the problem usually means wasting money on the wrong fix. LandTree serves Orange City, DeLand, Lake Mary, Sanford, Oviedo, Apopka, and the surrounding Seminole, Volusia, and Orange county areas. Contact us for a free lawn evaluation and we’ll identify exactly what’s going on and recommend the simplest effective treatment to get your grass green and healthy again.