How to Get Rid of Sod Webworms in Your Lawn

Sod webworms are the larval, caterpillar stage of lawn moths, and their favorite snack is your grass. You can get rid of sod webworms and keep them from coming back with a few targeted steps.

Below, we start with how to get rid of sod webworms, then cover how to spot and confirm them, prevent the next infestation, and explain what these pests are.

If hunting for caterpillars at dusk is not your idea of fun, Lawn Love’s lawn treatment service can take the pest problem off your hands.

How to get rid of sod webworms in your lawn

To get rid of sod webworms, treat the larvae with a biological or chemical product in the early evening, when the caterpillars come out to feed. You have several biological and chemical treatment options to choose from:

Biological control options

Biological products target the larvae while going easy on your lawn, and most are budget-friendly for a DIY treatment.

Ben McGraw, professor and program coordinator of Turfgrass Science at Pennsylvania State University, says for most insects, including sod webworms, “targeted insecticide applications timed to young larval stages are most effective.”

And he says Bacillus thuringiensis and nematodes are most effective.

“Organic/biological options include entomopathogenic nematodes (effective against grubs, mole crickets, and webworms when soil moisture is adequate) and Bacillus thuringiensis for caterpillar pests like armyworms and sod webworms,” McGraw says.

Here is how the most common options compare:

Biological option	How it works	Application tip
Bacillus thuringiensis (Bt), kurstaki or aizawai	A bacteria that works best on young larval stages	Washes off with water, so reapply after rain or watering, and apply in the early evening
Nematodes	Steinernema carpocapsae, a beneficial nematode that attacks larvae in the soil	Keep soil moist so the nematodes stay active
Azadirachtin	A compound from the neem tree, just like neem oil	Reapply as directed, since it breaks down quickly
Spinosad	A bacteria-derived organic pest control that controls lawn caterpillars	Let it dry before bees come out, as it is toxic to bees while wet

These options are easy on the wallet too. Bottled Bt runs about $12 to $45 and spinosad about $15 to $25, per Lawn Love’s organic treatment costs guide.

Note: There are different types of Bt, so make sure you buy the Bt with “Kurstaki” or “Aizawai” at the end of the name.

Chemical control options

Here are a few active ingredients to look for that will control sod webworms in your lawn:

• Acephate

• Carbaryl

• Cyfluthrin

• Ethoprop

• Trichlorfon

If you do not want to go to the store with a list of active ingredients in hand, keep it simple. Most insect control products at the big box stores (granular or liquid) will control sod webworms. Even if you do not see sod webworms on the front of the product, read the list of bugs on the back. Sod webworms are likely included in that list.

When to treat sod webworms: Whether you use biological or chemical solutions, try to treat early in the season, when the pests are about one-quarter inch long, for the best results. This is usually about 2 to 3 weeks after you see the moths flitting about the lawn in late spring.

If you do not catch the first generation when they are young, apply as soon as you have positively identified this bug. Sod webworms come out after the sun sets, so apply chemicals in the early evening to spray right as they come out to feed.

Note: Not all webworm damage requires treatment. Stronger, healthier lawns may resist and recover from damage without treatment, while lawns that are already stressed may benefit from treatment.

How to spot and confirm sod webworms

Sod webworm damage usually starts as small spots of browning turf that grow and coalesce as feeding continues. Patches are irregular in shape and start to thin and turn brown.

If you want to know whether these brown patches are due to sod webworms, here are 4 ways to check:

1. Hands and knees test

Sod webworms feed at night, so go into the lawn around dusk. Look for an area of damaged turf, and get on your hands and knees to look through the brown grass. You may see:

• Tiny worms crawling about

• Green-colored frass (excrement)

• Eggs

Also, look on the blades of grass. You will see irregularly shaped bite marks on the blade with yellowing or browning where it has been chewed.

Fun fact: Some species of sod webworm caterpillars are translucent, and if they have been munching on your grass, you will see the green foliage in their intestinal tract.

2. Drench test

If you cannot spot them on your hands and knees, bring them to the surface with a drench test.

“A soap flush (diluted dish soap in water poured over a marked area) brings larvae to the surface within minutes,” McGraw says. “Do this in the evening when they’re active.”

• Choose an area at the edge of the damage, where healthy grass meets brown turf, since active larvae feed at the advancing margin

• Mark out an area in the lawn that is 1 square yard in size

• Add 1 ounce of dish soap to 1 gallon of water

• Pour the water over the area

• If there are more than 15 larvae (healthy lawn) or 5 larvae (stressed turf) per square yard, consider treatment.

3. Look for moths

This is not a tip on how to ID sod webworms, but it is another way to help determine if they are in your lawn.

Moths are the adult version of sod webworms. If you go into the lawn in the evening and see moths flying just above the grass, that is another good indication that you have (or will have) webworms munching on your lawn.

Moths release their eggs onto the grass in the early evening or late afternoon as they flit about. Within a week or so, the eggs hatch and the larvae start to feed.

Note on feeding: Sod webworm larvae do the most damage (chomping and chewing) in their later larval stages. Damage in the earlier larval stages turns grass leaves into “leaf skeletons” and may be easy to miss.

4. Keep an eye out for birds

There are many reasons for birds to be in your yard, but they can indicate pests like sod webworms in your lawn. If you notice more birds in your yard, especially if they land in these newly brown spots, check to see if sod webworms or another tasty insect is to blame.

How to prevent sod webworms in your lawn

Preventing sod webworms or managing a small infestation is very doable. Here are a few DIY tips on how to get there:

Proper lawn care

Basic lawn care is your best friend if you need to strengthen your lawn against sod webworms or any other recurring insect issue. Sod webworms feed on warm-season and cool-season lawns (see charts below), so we will include information for both.

Fertilize sparingly: Sod webworms and many other grass-dwelling insects love it when homeowners over-fertilize their lawns. Too much fertilization increases thatch levels (in some grasses) and provides lots of tender top growth, which insects love to munch on.

Cool-season grasses	Fertilizer (in pounds nitrogen per 1,000 sq. ft. per year)
Fine fescue	1-2 pounds
Kentucky bluegrass	1-5 pounds
Perennial ryegrass	1-5 pounds
Tall fescue	1-3.5 pounds

Warm-season grasses	Fertilizer (in pounds nitrogen per 1,000 sq. ft. per year)
Bahiagrass	1-4 pounds
Bermudagrass	1-4.5 pounds
Carpetgrass	Optional, up to 2 pounds
Centipedegrass	0.5-2 pounds
Seashore paspalum	2-4 pounds
St. Augustinegrass	2-6 pounds
Zoysiagrass	0.5-2.5 pounds

Remove thatch and collect clippings: If you have an infestation of sod webworms, removing some of the thatch layer might help. A thatch layer over one-half inch encourages many insects, not only sod webworms.

Dethatching your lawn during an infestation also removes some of the eggs and larvae living on the thatch layer. Collect your clippings as you mow for the same reason.

Mow at the correct height: Believe it or not, your grass has been bred to be cut at a certain height. Anything taller or shorter, and it will not perform at its best.

Cool-season grasses	Mowing height
Fine fescue	1.5-3 inches
Kentucky bluegrass	2-3 inches
Perennial ryegrass	2-3 inches
Tall fescue	2-4 inches

Warm-season grasses	Mowing height
Bahiagrass	3-4 inches
Bermudagrass	1-2 inches (non-hybrid varieties)
Carpetgrass	1-2 inches
Centipedegrass	1.5-2 inches
Seashore paspalum	1-2 inches
St. Augustinegrass	2.5-3 inches for dwarf cultivars; 3-4 inches for standard cultivars
Zoysiagrass	1-2.5 inches

Water well: Sod webworms congregate in dry, drought-stressed areas, so irrigation is important. Water loam and clay soils once per week with 1 to 1.5 inches of water. Sandy soils need watering two to three times per week (same total amount of water) since they do not hold water well.

Choose resistant grasses

Endophyte-enhanced grasses, namely certain types of perennial ryegrass and fescues, help deter sod webworms from munching on your grass. There are no Kentucky bluegrass (KBG) cultivars with endophytes, but you can overseed with either of these other cool-season grasses to give a KBG lawn greater resistance.

As for warm-season grasses, here are a few St. Augustinegrass and Zoysiagrass cultivars that resist sod webworm feeding:

St. Augustine (moderate resistance):

• Amerishade

• Captiva

• Floratine

• FX-10

• Winchester

Zoysia (high resistance):

• Cavalier

• DALZ8501

• JZ-1

Sod webworm basics

Sod webworms are the caterpillar or larval stage of what are commonly called “lawn moths.” It is only the caterpillar stage you need to worry about: The caterpillars munch on your grass blades, but the moth (adult) stage will not harm your lawn.

There are over 20 species of these lawn-loving caterpillars, and they are found throughout the country in most cool- and warm-season grasses.

Life cycle

There are four broad life stages for sod webworms:

Egg: Adult sod webworm moths deposit egg masses in the grass as they fly over the lawn on late spring evenings. Eggs hatch in roughly one to two weeks.

Larvae: After hatching, small larvae start to feed on the surface of the grass blade. This “superficial” damage can be hard to spot. As larvae get older, they chomp and notch into the blade as they feed, which is much easier to see.

Sod webworm caterpillars go through several larval stages before they turn into a pupa. The entire life cycle, from egg to adult, takes three to seven weeks, depending on the temperature.

Pupa: After the webworm larvae finish growing, they turn into pupae, which live in the upper thatch layer until they emerge as moths (adults).

Adult: Adult sod webworms, like butterflies, are no longer caterpillars but have blossomed into a completely different creature, a moth.

Depending on the species and the climate, there can be from one to four generations each year. Near the end of the season, most larvae weave a home for themselves and overwinter cozily tucked into the soil.

With the arrival of spring, they emerge, feed, pupate, and turn into adults (moths) by late spring and start the life cycle over again.

Feeding behavior

Sod webworms, as their name suggests, like to munch on grass. As nocturnal insects, they act like vampires, munching the life out of your lawn before sunrise.

Here are the common cool- and warm-season grasses sod webworms munch on most often:

Cool-season grasses:

• Fine fescue

• Kentucky bluegrass

• Perennial ryegrass

Warm-season grasses:

• Bahiagrass

• Bermudagrass

• Carpetgrass

• Centipedegrass

• Seashore paspalum

• St. Augustinegrass

• Zoysiagrass

Size and appearance

Larvae range in size from three-quarters to 1 inch long when fully grown. Although their coloration varies by species, most have a brown head with a body color that can be translucent, beige, brown, gray, or green. Pupa cases range from tan to dark brown. The tropical sod webworm, a common species in warm climates, has a red-brown pupa case.

Adult moths are a dull, light brown or buff color with a wingspan of about three-quarters to 1 inch. They have two projections that protrude from the top of their head and for this reason are sometimes called “snout moths.”

FAQs

Let Lawn Love handle your sod webworm problem

Diagnosing brown patches, timing treatments for nighttime feeders, and keeping your grass strong enough to shrug off pests is a lot to juggle. That is where a pro comes in.

Do not let sod webworms mar your green expanse of lawn. Let one of Lawn Love’s local lawn care pros diagnose, treat, and restore your lawn’s green hue.

Main photo credit: Christopher Stephens | Wikimedia Commons | CC BY-SA 4.0