Cutworms in St. Charles County Lawns: Nighttime Damage and How to Stop It

If you find small brown patches of grass that look like they were clipped off at the base, with the chewed blades still lying there, you’re probably dealing with cutworms. They feed at night and hide during the day, so the damage can look like it happened by itself. Around St. Charles County, they show up most often in spring and again in late summer, and they’re especially hard on newly seeded lawns.

What Are Cutworms?

Cutworms are the caterpillar stage of several species of night-flying moths in the Noctuidae family. The name comes from what they do: they cut grass plants and seedlings off at the base, just above the soil line.

The most common one in Missouri is the black cutworm. MU Extension notes that black cutworms don’t reliably overwinter here. Instead, moths ride spring storm fronts up from the south, lay eggs, and the larvae start feeding a few weeks later. That’s why damage often shows up suddenly in May or June, then again in late summer as a second generation builds.

You’ll rarely see the caterpillars during the day. They feed at night, then curl up in the thatch or the top inch of soil when the sun comes up. If you dig around in a damaged spot in the morning, you can often find them: smooth, grayish-brown caterpillars, usually an inch or a little less, that curl into a C or a tight spiral when disturbed.

What Cutworm Damage Looks Like

Cutworm damage is distinctive if you know what to look for:

• Small, irregular brown patches scattered across the lawn, often worse near the edges of the yard or along sidewalks and driveways.
• Grass blades chewed off at the base, with the clipped pieces lying loose on the surface or caught in the thatch. It looks like someone took scissors to the lawn.
• Damage that appears overnight or over a couple of nights, not a gradual browning.
• In newly seeded areas, whole patches of seedlings may vanish in one night. Cutworms are one of the biggest reasons a fresh seeding fails.

The feeding pattern is different from most other lawn pests, which is why the comparison matters.

Cutworm vs Armyworm vs Sod Webworm vs Grub

This is where people get tangled up. Several pests make brown patches in a St. Charles County lawn, and the fix is different for each one.

Sign	Cutworms	Armyworms	Sod webworms	Grubs
Where they feed	Chew blades off at the base	Eat blades from the top down	Chew blades, live in silk-lined tunnels	Eat roots below the soil
Damage pattern	Small scattered patches, worse at edges and in new seed	Large areas stripped fast, marching pattern	Irregular brown patches, often near a dry or thin area	Turf lifts up like carpet, roots gone
When they feed	At night	Night and early morning	At night	All day, below ground
How to spot them	Curled up in thatch/soil in the morning	Caterpillars in the thatch, birds working the lawn	Small tan moths flying at dusk; caterpillars in silk tubes	White C-shaped grubs under lifted turf

Quick version: cutworms clip at the base, armyworms eat from the top, webworms work from tunnels, and grubs eat roots. If you can pull up dead turf like a carpet and find C-shaped white grubs, that’s grubs, not cutworms. You can read more in our guide to white grub control.

If the blades are chewed down to stubs and there are caterpillars in the thatch, compare them to our armyworm guide and our sod webworm guide. Armyworms and webworms are much more common in Missouri lawns than cutworms, but cutworms are the ones that hit new seedings hardest.

The Soapy Water Test

Same test we recommend for every lawn caterpillar. A bucket, dish soap, and ten minutes will tell you what you’re dealing with.

1. Mix about a tablespoon of liquid dish soap into a gallon of water.
2. Pour it slowly over one square yard of turf at the edge of a damaged patch.
3. Wait five to ten minutes.

The soap irritates caterpillars and drives them to the surface. Cutworms will crawl out, curl up, and be easy to identify. If you find four or five or more per square yard, treatment is worth it. A couple here and there is normal and not worth spraying.

If nothing comes up, keep looking. The damage could be fungus, drought, or another pest, and treating the wrong thing wastes money and time. Our lawn fungus identification guide covers the disease side.

How to Treat Cutworms

The good news is cutworms are easy to knock down if you catch them small. The bad news is that once they’re mature, they’re tougher, and the biggest ones are hard to kill with anything.

For small caterpillars: Bacillus thuringiensis, sold as Bt, is about as gentle as a lawn insecticide gets. It only affects caterpillars, and it works well on young cutworms that are still feeding on leaf tissue.

For most home infestations: Products with spinosad, bifenthrin, lambda-cyhalothrin, permethrin, or deltamethrin are labeled for cutworms. Bifenthrin and lambda-cyhalothrin are the common active ingredients in granular lawn insecticide products you can spread with a regular spreader.

Timing matters. Treat in the late afternoon or evening. Cutworms are active at night, and they need to come in contact with the product. A daytime application that dries before they move around is a wasted application.

Water in granular products after applying, same as any lawn insecticide, and follow the label rate exactly. More is not better.

The New Seeding Problem

This is the situation where cutworms do the most damage, and it’s worth calling out on its own.

If you overseeded in the spring, or you’re planning a fall renovation, know this: a fresh seeding is a cutworm buffet. The seedlings are tender, low to the ground, and exactly what the caterpillars are built to eat. One night of feeding can take out a whole section of new grass, and by the time you notice, the larvae are gone and hiding.

For fall overseeding in St. Charles County, the standard advice is to apply a preventive insecticide with the seeding, water it in, and treat again if you see clipping damage. Fall is the best time to seed a fescue lawn in Missouri, and protecting that investment is part of the job. Our guide to choosing the best grass seed for overseeding covers the seeding side.

If you’re renovating a larger area, a local provider can apply the right product at the right rate and time it with the seeding, which takes the guesswork out of it.

Preventing Cutworms

You can’t stop the moths from blowing in on a storm front, but you can make your lawn less inviting and catch problems early.

• Watch new seedings closely. This is the highest-risk window. Check seeded areas every morning for clipped seedlings.
• Keep an eye on the lawn edges. Cutworm damage often starts where the turf meets hard surfaces, so check sidewalks, driveways, and patio edges first.
• Encourage birds. Robins, grackles, and starlings eat caterpillars. A lawn that gets bird attention is a lawn with fewer larvae.
• Don’t overdo the thatch. Heavy thatch gives caterpillars a place to hide during the day. Core aeration and regular mowing keep it in check.
• Keep the turf healthy. A dense, well-maintained lawn survives light feeding and recovers faster than a stressed one. That’s true for every pest we deal with around here.

Helping the Lawn Recover

Once the caterpillars are gone, the lawn needs a little help to fill back in.

• Water. Deep, infrequent watering keeps the crowns hydrated. Don’t let the lawn go bone dry during recovery.
• Hold the heavy fertilizer. Light nitrogen, around 0.75 to 1 pound per 1,000 square feet, is enough. Skip anything aggressive in the summer heat.
• Wait for fall to seed. If the damage is thin but the crowns survived, fescue will start filling in as temperatures drop. If areas are bare down to dirt, plan to overseed this fall rather than doing a rushed summer patch job. Our fall lawn renovation planning guide walks through the timing.

When to Call a Professional

Call someone if you’re not sure what you’re looking at, if the damage is spread over a large area, or if you tried a treatment and the clipping is still happening. A local provider can confirm cutworms, apply the right product, and handle the fall overseeding if the lawn needs it.

A good provider should be able to tell you what they found and what they’re using, and why. If you get a vague answer, that’s a red flag.

---

Not sure whether those brown patches are cutworms, armyworms, grubs, fungus, or just summer stress? Get matched with a local provider who can look at your yard and give you a straight answer.