Sod Webworms: How to Identify, Treat and Protect Your Lawn

What are Sod Webworms and Signs of Damage?

Sod webworm, also known as lawn moths, are white to tan-colored moths that appear to randomly flit over your lawn’s canopy during the summer as you walk through. These lawn pests don’t fly far before landing again.

Effective lawn pest management starts with properly identifying the sign of sod webworm damage. While the adults flutter at dusk, it’s the grass‑munching larvae you should worry about. You’ll recognize them by the irregular classic brown patches.. These hungry little caterpillars munch on grass leaves right down to the surface, potentially killing the grass plant.

What Are the Types of Sod Webworms?

Entomologists suggest there are up to 20 species of sod webworm. They’re a diverse bunch, occupying a broad geographic area and adapting to different climates and growing conditions. They all share similar characteristics:

• They follow the same four developmental growth stages:
  • Egg;
  • Larvae;
  • Pupae;
  • Adult moth.
• Most produce two and sometimes three generations each season.
• They feed on bluegrass, fine fescue, perennial ryegrass and zoysiagrass lawns.

What Impact do Sod Webworms Have on Lawns?

If you notice tiny, triangular‑winged moths fluttering over sun‑baked grass, it’s an early warning sign of hungry larvae below. These moths don’t damage your lawn. However, as they fly around, the females drop eggs up to 200 of them!

About a week after hatching, the hungry caterpillars go to town. You usually don’t know they’re there until you notice turf damage. If left unchecked, a severe outbreak of caterpillars can kill large portions of your lawn.

What Are the Signs of a Sod Webworm Infestation?

• First, you’ll see small saucer-sized brown patches in your lawn. Looking closer, these are the result of grass leaves being chewed down to the soil surface.
• You’ll see sod webworm moths flying around in the late afternoon or early evening, right before dusk.
• The caterpillars themselves are nocturnal. They feed during the night, so it’s hard to see them in action.
• As the caterpillars munch away, the smaller brown patches expand, taking on the appearance of drought-stricken turf.

Determine the Infestation With the “Floatation Method”

• Mix one to two tablespoons of lemon-scented dish detergent in one or two gallons of water.
• Drench an area about two feet square near the edges of the damaged area. This is where the larvae are feeding. The solution will irritate the caterpillars, so they’ll wiggle out of the thatch and come to the surface.
• Wait two to five minutes and count the caterpillars.
• If you see more than 15 to 20 larvae per square foot, a control remedy may be needed.

How to Treat Sod Webworms?

Most lawn insecticides effectively control sod webworm without breaking the bank. When selecting the best pesticides for turf damaged by webworms, consider these proven, budget‑friendly options for long‑lasting protection.

Sprayable insecticides like Ortho’s BugClear Insect Killer For Lawns and Bonide Pyrethrin Outdoor Insecticide eradicate sod webworm as well as a host of other surface-feeding insects. Make sure to evacuate the space completely before spraying to ensure the safety of kids and pets. Only re-enter the area once it has fully dried. Additionally, follow the instructions on the product for correct use.

If you want to use a fertilizer spreader rather than a lawn sprayer, there are some good granular options. Anderson’s DuoCide Professional Grade Lawn Insect Control is one of my favorites. As the name implies, it’s what the pros use. Spectracide Triazicide Insect Killer is another good choice for sod webworm and many other surface-feeding insects. A comprehensive lawn pest management strategy includes both treatment and prevention methods.

Water your lawn a day or two before applying conventional insecticides. Once the insecticide has been applied, lightly water the product into the ground. This washes the active ingredient off the grass blades and into the thatch layer where the caterpillars live. The best time to treat your lawn is late afternoon or evening, just before the caterpillars come to the surface to feed.

Biological options also work reasonably well for controlling sod webworms. Bacillus thuringiensis (subspecies kurstaki) is a beneficial bacterium, producing a natural toxin that paralyzes the caterpillars. Biological products take longer to work, but they’re safe for humans and pets and good for the environment.

Consider options like Monterey Bacillus Thuringiensis Worm and Caterpillar Killer Insecticide or Southern Ag Thuricide BT Caterpillar Control. You’ll find most Bacillus thuringiensis products are sold for use in gardens, but they are just as effective as a lawn treatment.

How to Keep Sod Webworms from Coming Back

Once you’ve won the battle against sod webworms, you need to prevent them from returning.

• First and foremost, take good care of your lawn! Like most lawn pests, sod webworms always attack a weakened lawn first. By properly fertilizing, watering, core aerating and mowing properly, your grass will be healthy enough to fend off just about any challenge.
• Keep your mowing height in the three- to four-inch range. Cutting your lawn too short can cause scalping and thin turf. This makes your lawn dry out quicker, which makes it more susceptible to pests.
• Reseed your lawn with endophyte-enhanced grass seed varieties.

Endophytes are intracellular fungi that live within the grass plant and they help many turf species prosper. Toxic compounds produced by the endophytes can deter insects from chewing on grass leaves and stems because they don’t taste good. Endophytes also help with overall heat stress in lawns and can suppress some lawn diseases.

Not all lawn species have endophytes, however. Kentucky bluegrass doesn’t. But some perennial ryegrasses, fine fescue and tall fescue varieties do.

How do you know if the varieties in your lawn seed mix are endophyte-enhanced? That’s the hard part. If you’re lucky, the grass seed label will tell you. If not, search for that information online. University extension services are a good place to start.

The ability to recognize the sign of sod webworm damage early and know how to treat sod webworms effectively is important to keeping a lawn healthy. If you take the right combination of the best pesticides for turf and lawn pest management techniques, you can protect your grass from these destructive insects.

FAQ

What are the most common signs of sod webworm damage?

Some of the first symptoms include small brown patches, chewed grass blades and moths at dusk.

What are the best pesticides for turf affected by sod webworm?

Some of the recommended ones contain Bacillus thuringiensis, pyrethrin, or any of the professional insecticides, such as The Andersons DuoCide.

How does proper lawn pests management prevent sod webworm infestations?

Regular maintenance, proper mowing height and using endophyte-enhanced grass varieties all contribute to a comprehensive lawn pest management strategy.

Sources

• Texas A&M AgriLife Extension Service: “Tropical Sod Webworm.” 
• Texas A&M University: “Sod Webworm.” Field Guide to Common Texas Insects.
• Senske Services: “Sod Webworm Treatment.”