Billbugs in Lawns: Root-Feeding Weevils and How to Stop Them

If a patch of your St. Charles County lawn turned brown in the last couple of weeks and the grass pulls out of the ground like a loose carpet, billbugs are a real possibility. Billbugs hollow out grass stems from the inside, and by August the damage is finally visible. Here is how to confirm them, what you can do right now, and what has to wait until fall.

What Are Billbugs?

Billbugs are weevils — snout beetles — not true grubs. The adults are small, hard-shelled beetles about a quarter to three-eighths of an inch long. They have a long snout, which is the quickest way to recognize one, and they range from dull brown to almost black. You’ll rarely notice them unless you’re looking, because they hide in the thatch and around the base of the grass during the day.

The larvae are the ones that do the damage. Billbug larvae look like small, legless, cream-colored grubs with a brown head capsule. If you’ve read our guide to white grubs, you know true grubs are C-shaped, whitish, with distinct legs. Billbug larvae are different — no legs, no C shape, and they live inside the grass stems, not down in the soil. That difference matters, because it changes how you treat them.

Two species matter most in Missouri:

• Bluegrass billbug — mainly attacks Kentucky bluegrass, though it will feed on other cool-season grasses when bluegrass isn’t around.
• Hunting billbug — the one more likely to hit tall fescue, which is what most St. Charles County lawns are.

How Billbugs Damage Your Lawn

Here’s the part that surprises people: billbug larvae don’t chew roots the way grubs do. They tunnel up and down inside the grass stems, hollowing them out as they feed on the tissue at the base of the plant. When enough stems are hollow, the grass can’t take up water, and it dies from the crown up.

That’s why the damage shows up the way it does:

• Patches appear in mid to late summer, often right when lawns are already stressed by heat and dry weather.
• The damaged grass pulls out easily — it comes up in clumps with the stems still attached, like a piece of loose carpet.
• If you split a pulled stem open, it’s hollow. You may see fine, sawdust-like material (frass) packed at the base where the larvae have been feeding.

In our part of Missouri, August is when homeowners finally notice it. The adults were active back in June and July, laying eggs near the base of the grass. The larvae hatched, fed for several weeks, and by now the damage is catching up with the lawn. It’s easy to mistake for drought stress, fungus, or grub damage — so before you treat anything, check.

Billbug Damage vs. Grubs vs. Drought

Use this table to sort out what you’re looking at:

What you see	Likely culprit	How to confirm
Grass pulls out in clumps, stems hollow, sawdust-like frass at the base	Billbugs	Split a stem — hollow inside, larvae inside or in thatch
Dead patches that peel back like sod, roots chewed off, C-shaped grubs in soil	White grubs	Dig under the patch — grubs in the top few inches of soil
Brown patches that stay rooted, blades just brown, lawn rebounds with rain	Drought stress	Tug test — grass stays put, no hollow stems, no insects
Irregular brown patches with a frog-eye pattern, white fungal growth at the edges in damp weather	Fungus (brown patch)	Look for the classic ring pattern; our fungus guide walks through it

The pull test is the fastest way to separate billbugs from drought. Drought-stressed grass is still anchored. Billbug-damaged grass comes up in your hand, and the stems are hollow.

How to Check for Billbugs

You don’t need a lab for this. Walk the edge of the damaged area and try the pull test on a few spots. If grass comes up easily, take a stem and split it lengthwise with your thumbnail. Hollow stem with frass inside — that’s billbug larvae at work.

A couple of things to keep in mind:

• The soap flush test doesn’t work for billbugs. It’s a great tool for sod webworms and chinch bugs, but billbug larvae live inside the stems and adults hide in thatch, so flushing them out is hit or miss.
• Adults are the sign to watch in early summer. If you were seeing small snout beetles crawling around near the base of the grass in June or July, that was your warning.
• Damage can lag the infestation. By August, the larvae may already be done feeding and starting to pupate. Finding hollow stems now tells you what happened — it doesn’t mean there’s an active infestation to spray.

That last point is important, so let me be direct about it: spraying insecticide in August is usually too late to help this year. Billbug control is a timing game, and the timing is early summer.

Billbug Treatment: What Works and When

Prevention (the part that actually works)

The standard approach is a preventive insecticide applied when the adults are active — typically late June through early July in our area. Products containing imidacloprid, clothianidin, or thiamethoxam are the common choices, and many of them are the same products used for grub prevention. If you’re already putting down a grub preventer in June or July, you may already be covering billbugs.

A few rules:

• Time it to the adults, not the larvae. Apply when adults are active and laying eggs, before the larvae tunnel into the stems.
• Water it in. These products need to be moved into the thatch and soil where the insects are. A light watering right after application makes a real difference.
• Read the label for the target pest. Not every grub product lists billbugs. Check the label before you assume.

Curative control (limited)

Once larvae are inside the stems in August, contact insecticides don’t reach them well. Some lawn pros will apply a product with a different mode of action to try to catch late-hatching larvae, but results are inconsistent. Honestly, most of what you do in August is damage control: water the lawn enough to keep surviving grass alive, raise the mower height, and plan the fall recovery.

What not to do

Don’t douse a brown patch in August with insecticide hoping it will come back. It won’t, and you’ll just kill beneficial insects for nothing. Don’t scalp the lawn either — that stresses fescue further in the hottest part of the year. Our guide on fixing bare spots in summer covers what you can actually repair now versus what waits for fall.

Recovery and Prevention for Next Year

Here’s the practical plan for St. Charles County lawns after billbug damage:

1. Keep watering during dry spells. Damaged grass has less root and stem structure, so it dries out faster. Consistent, deep watering early in the morning helps the surviving plants hang on.
2. Raise the mower. Taller fescue is deeper-rooted fescue. During summer heat, mow at the higher end of the range and let the grass shade its own soil.
3. Plan fall renovation. Billbug damage in August means the lawn is thin going into fall. Aerate and overseed in September, when the heat breaks. Our fall lawn renovation planning guide walks through the timing.
4. Consider endophyte-enhanced fescue seed. Some tall fescue varieties are bred with endophyte fungi that make the plant unpalatable to billbugs and other stem-feeding pests. When you overseed this fall, it’s worth asking about endophyte-enhanced seed.
5. Mark June on the calendar. If billbugs were a problem this year, plan the preventive application for next June or July. That’s the single highest-value thing you can do.

One more note: billbug larvae also attract skunks and birds that dig for them. If you’re seeing shallow digging in the lawn at night, that’s another clue worth checking.

When to Call a Professional

If you’re not sure whether the damage is billbugs, grubs, fungus, or just August, get a local set of eyes on it before you spend money on products. A provider who knows St. Charles County lawns can do the pull test, check the stems, and tell you whether treatment makes sense this year or whether the move is damage control now and renovation in the fall.

That’s exactly what Midwest Lawn Care is for. Tell us what you’re seeing — the patches, the pull test, anything you’ve already tried — and we’ll connect you with a vetted local provider who can take a look. Request lawn care help here, and we’ll take it from there.

Last updated: August 14, 2026. Billbug biology and control timing based on University of Missouri Extension and NC State TurfFiles guidance for cool-season lawns in the transition zone.