White Grubs in Your Lawn: Japanese Beetles, June Bugs, and Masked Chafers

The short version: if your St. Charles County lawn has brown patches that peel up like loose carpet in August, white grubs are likely the culprit. Those C-shaped cream-colored larvae are Japanese beetle, June bug, or masked chafer grubs chewing on grassroots below the surface. Here’s how to confirm them, which species you’re dealing with, and what actually works to stop them.

What Are White Grubs?

White grubs are the larval stage of beetles that are common across Missouri: Japanese beetles, June bugs (May/June beetles), and masked chafers. They live underground, feed on grass roots, and turn into the adult beetles you see flying around porch lights in early summer.

The damage is invisible at first. Grubs eat roots below the soil surface, so the grass above looks fine until the roots are too damaged to take up water. That’s when you see brown patches — usually in late July through September, right when the grubs are at their biggest and hungriest.

Key identification facts:

• C-shaped body, cream to grayish-white color
• Brown head capsule, six small legs near the front
• Size ranges from 1/4 inch (young) to about 1 inch (mature)
• Found in the top 1–3 inches of soil, right below the grass

Which Grub Is In Your Lawn?

Missouri lawns get three main species. They look similar but have slightly different habits:

Species	Adult Beetle	When Adults Fly	Grub Notes
Japanese beetle	Metallic green with copper wings	Late June–July	Most common in well-watered, sunny lawns; most damaging
May/June beetle (June bug)	Brown, chunky, noisy flier	May–June	Bigger grubs, often found near trees and edges
Masked chafer	Tan-brown, small, attracted to lights	Late June–July	Common in irrigated lawns; grubs look nearly identical to Japanese beetle

Around here, Japanese beetle grubs cause most of the serious damage. The adults skeletonize rose bushes and linden trees in July, then lay eggs in moist, well-watered lawns. If you saw adult Japanese beetles this summer, those eggs are hatching right now.

How to Confirm Grubs (Two Tests)

Don’t guess. Two quick checks tell you if grubs are actually the problem:

1. The tug test. Grab a handful of dead or browning grass near the edge of a patch and pull. If the grass comes up easily, like a loose carpet with little to no root attached, grubs have eaten the roots. If it resists, roots are intact and something else is going on.

2. The shovel test. Cut three sides of a 1-foot square of turf, about 2–3 inches deep, and fold it back like a flap. Count the grubs in the soil and grass roots. University extension guidance treats about 5–10 grubs per square foot as the damage threshold for irrigated lawns — below that, the lawn usually survives on its own.

Do the checks in a couple of spots, not just one. Grub numbers vary across a yard.

Grub Damage vs. Everything Else

Brown patches in August have several causes, and treating the wrong one wastes money. Here’s how to tell them apart:

Problem	What It Looks Like	Quick Test
White grubs	Patches peel up like carpet; no roots left	Tug test + shovel test
Drought/heat stress	Uniform browning, often on slopes and thin soil	Grass stays rooted; recovers with water
Armyworms	Grass chewed down to stubs, looks scalped overnight	Look for caterpillars; soapy water flush
Chinch bugs	Irregular dead patches, often sun-exposed areas	Coffee can test — small bugs float
Brown patch fungus	Circular tan patches with dark ring	Grass stays rooted; no insects in soil

If you’re not sure, the armyworm guide and chinch bug guide cover the other late-summer culprits, and the lawn fungus identification guide covers the disease side. Grubs are the one cause where the turf physically separates from the soil.

The Life Cycle and Why August Matters

Grub timing in Missouri follows a predictable schedule:

• Late June–early July: Adult beetles lay eggs in moist soil
• Mid-July–August: Eggs hatch; young grubs feed near the surface
• August–September: Grubs grow fast, cause the most visible damage
• October–November: Grubs move deeper to overwinter
• Following spring: They move back up, feed briefly, then pupate into adults

The window that matters for treatment is earlier than most people think. Preventive grub control needs to go down by mid-July — before eggs hatch — to work at its best. If you’re reading this in August with damage already showing, you’re in curative territory, and the options are different.

What to Do If You Have Grubs Now

If you’re seeing damage in August:

• Confirm the count first. A few grubs per square foot isn’t worth treating; healthy fescue can outgrow minor root loss.
• Water deeply but less often. Lawns with deep roots tolerate grub feeding much better than shallow-rooted, frequently watered lawns.
• Consider a curative insecticide labeled for grubs (products containing carbaryl or trichlorfon). These work on larger, actively feeding grubs. Follow label rates exactly — this is not a job for guessing.
• Skip the blanket preventive application if the season is already past the window. You’ll get better results from a properly timed preventive next year.

If you want to prevent next year’s problem:

• Plan a preventive application (imidacloprid or chlorantraniliprole) for next June–early July, timed to the egg-lay window
• Milky spore and beneficial nematodes are options, but they work slowly and results vary on Missouri clay soil — understand the trade-offs before relying on them
• Healthy, well-managed turf is the best defense; stressed lawns attract beetles and recover slower

The full breakdown of timing and product choices is in our grub control timing guide.

Will the Lawn Recover?

Yes, with the right follow-up. Once grubs are controlled, fescue can send out new roots, but recovery takes time and conditions matter:

• Keep the lawn watered through recovery — grub-damaged roots can’t handle drought stress
• Hold off on heavy foot traffic over damaged areas
• If patches are large and bare, plan aeration and overseeding in September. Our fall lawn fertilizer guide covers the recovery feeding schedule
• The August lawn care guide has the full month’s maintenance list

FAQ

Are grubs harmful to people or pets? No. They live underground and don’t bite or sting. The damage is to the grass roots only.

Can I treat grubs myself? Yes, if the infestation is small and you can follow label rates precisely. Granular products need to be watered in to reach the soil. For larger areas or if you’re unsure of the diagnosis, it’s worth getting a local pro to look.

Do grubs come back every year? They can. Adult beetles fly in from neighboring yards, so prevention isn’t a one-and-done. An annual preventive application, timed correctly, keeps numbers low.

Is grub damage the same as what killed my lawn last winter? Not usually. Winter damage on Missouri lawns is more often snow mold, desiccation, or vole activity. Grub damage is a late-summer problem.

When to Call a Professional

Grub control is one of those jobs where DIY can work, but only if the timing and product match the situation. If you’re seeing large patches, aren’t sure grubs are the cause, or just don’t want to spend August fighting it alone, a vetted local provider can confirm the diagnosis, treat it right, and set up next year’s prevention.

That’s what Midwest Lawn Care is here for — tell us what your lawn is doing and we’ll point you in the direction of a dependable local provider who fits the job. Get a quote and we’ll help you compare your options.

Last updated: August 12, 2026