Japanese beetle grubs damage turfgrass roots and challenge Ohio lawns.

Root trouble beneath the green: why Japanese beetle grubs steal turf’s life

There’s something unnerving about a patch of lawn going from lush to dull overnight. You pull back a bit of sod, and suddenly the roots look pale, the soil is loose, and the grass above it barely clings on. The culprit isn’t always drought or a bad fertilizer plan. Often, it’s what you can’t see that does the most damage: grubs feeding on the turfgrass roots underground. And in Ohio, the grubs that cause real root damage are the larvae of Japanese beetles.

Let me explain what makes these grubs so notorious

Grubs from the Japanese beetle are white, C-shaped larvae that live in the soil as they grow. They’re the inside jobbers of turf health. As they feed on the roots, they disrupt the plant’s ability to take up water and nutrients. The grass looks stressed, turns dull, and can even die if the infestation is heavy or the weather sours—think hot, dry days followed by a dry spell. When you poke at the turf, it may lift up like a carpet, revealing the grubs curled beneath.

Now, you might wonder: are all lawn pests dangerous to the roots? The quick answer is no. Grasshoppers mostly dine on the above-ground parts—leaves and stems—so you’ll see holes in the leaves before you notice root trouble. Ants can be a nuisance in lawns, but they don’t typically munch the roots in numbers that cause widespread turf failure. Spiders, meanwhile, do their bit as beneficial predators, helping keep other pests in check rather than causing root damage. Grubs, on the other hand, are a root-focused problem—mostly because they’re right where the grass needs it most: in the soil, near the root zone.

Why grubs matter so much in Ohio

Ohio summers can be hot and sometimes dry, which is a setup that suits grub damage. Japanese beetle adults emerge in waves during the warm months, and their offspring—the grubs—settle into the soil where they gorge on grassroots. The timing is everything: if you have a healthy stand of turf with robust root systems, it can tolerate a light grub presence. If not, even a moderate population can push the lawn into decline. Ohio lawns often use cool-season grasses like Kentucky bluegrass, tall fescue, or fine fescue, which respond noticeably to root stress. In short, the Japanese beetle grubs have a knack for putting the life back into the soil’s quiet places—and that’s bad news for a lush lawn.

How to spot root damage without pulling the entire yard apart

Signs are usually a mix of symptoms you’ll see above ground and a few clues below ground:

• Patches of straw-colored or wilted turf that won’t recover after watering.

• A loosely rooted feel when you lift a small section of turf; the blades may stand up a bit, but the roots are gone or chewed.

• A spongy feel underfoot, especially in the root zone, where roots should be holding soil together.

• Increased thatch or loose soil layers in the root zone.

To confirm, you can check more directly:

• Do a simple pull test in a few planted spots. If you can lift a square foot of turf with little effort, that’s a red flag.

• Dig a shallow soil core (a few inches deep) and look for white, C-shaped grubs. They’re easiest to spot when the soil is moist but not muddy.

A word about the other pests

You’ll hear about a few other culprits in turf talks. Grasshoppers do most of their damage above ground, munching leaves and stems, which creates a different pattern than root damage. Ants can compete with turf roots for moisture and can disrupt the soil structure, but they aren’t the root-eaters that Japanese beetle grubs are. Spiders are more of a cleansing crew, snapping up smaller pests that could otherwise prosper in a stressed lawn. So if your lawn’s roots look chewed, it’s a strong hint the issue lies with grubs rather than harmless critters or surface pests.

What to do about grubs in Ohio lawns

A practical plan mixes cultural care with targeted controls. The goal isn’t to wipe out every grub on the planet in one go; it’s to keep the root zone healthy and to intervene when populations are likely to do real harm.

1. Build a healthier baseline for your turf

• Mow at the right height for your grass type. Taller blades shade the soil and help roots stay cooler and more resilient.

• Water deeply and less frequently. Deep watering keeps roots strong and makes the soil less hospitable to new grub generations.

• Aerate when the soil is compacted or when thatch builds up. Aeration improves water and air movement in the root zone, which helps the grass recover from stress and keeps it less inviting to pests.

2. Scout and monitor

• Check for grubs in late summer to early fall when they’re larger and easier to detect, or in late spring when new grubs begin feeding again. You’ll want to sample several spots in a lawn to get a realistic read.

• A rough threshold many turf managers use is finding about 5 or more grubs per square foot to justify control. Ohio State University Extension materials are a reliable reference for local guidance, and they emphasize assessing both grub numbers and the turf’s vigor before acting.

3. Biological options that respect the landscape

• Milky spore disease (Bacillus popilliae) is a long-term, soil-based solution specific to Japanese beetle grubs. It won’t deliver instant results, but over a few years it builds in the soil and reduces grub populations. It’s best used in established lawns and with a long-tail view.

• Beneficial nematodes (like Heterorhabditis bacteriophora or Steinernema spp.) are tiny nematodes that hunt grubs in the soil. They’re applied with irrigation and need moist soil conditions to stay active. When they find a grub, they release bacteria that kill it. This approach is more immediate than milky spore but still depends on weather and soil moisture.

4. Chemical controls—timing and precision matter

• Systemic insecticides can stop grubs when they’re small and still feeding near the root zone. Imidacloprid and certain other systemic products are commonly used, but their effectiveness depends on timing and turf species. Application is typically timed to target early instars.

• In some situations, other soil-applied insecticides that target grubs may be recommended. Always follow local regulations and label directions, and consider the health of pollinators and nearby water sources.

• If you’re unsure which product is right, consult with a turf care professional or your local extension office. They can tailor a plan to your lawn’s species, soil conditions, and climate.

5. Don’t rely on traps to save the day

• Pheromone or light traps often draw more beetles into the yard than they remove. The attraction can make things worse by concentrating pests in your space. The best approach is to focus on root health and timely treatment.

A few Ohio-specific tips you can put into action

• Timing is everything in Ohio. Grubs feed through late spring into summer, and the best target window for many controls is late summer when the grubs are smaller and easier to kill. If you’re considering a biological approach, start early in the season and keep soil moist to give nematodes a chance to work.

• Soil type and moisture matter. Sandy soils drain quickly; they can dry out fast, which stresses grass and makes damage feel worse. Clay soils retain moisture but can become compacted. In either case, aeration and proper irrigation help both the grass and any biological control agents do their job more effectively.

• Balance, don’t blow past cultural care. A strong, healthy lawn resists root damage better than a thin, stressed one. Think of it as a team effort: good mowing, smart irrigation, and targeted treatments work best together.

Real-world framing: what success looks like

If a lawn had a visible decline due to grubs, and you apply a well-timed, targeted approach, you often see recovery in a few weeks to a couple of months after the root zone regains strength. The color comes back, the patches fill in, and the turf’s resilience returns. The key is not chasing a perfect, zombie-free lawn overnight but building a sustainable plan that keeps roots intact and the soil healthy.

A quick takeaway touchstone

• Grubs from Japanese beetles cause root damage in turfgrass.

• Other pests don’t usually bite at the roots in the same way.

• Detect by checking for loose turf and white C-shaped grubs in the soil.

• Maintain turf vigor through proper mowing, irrigation, and aeration.

• Use biological controls for a long-term approach and consider targeted chemical controls when grubs are actively feeding.

• Traps aren’t a silver bullet; focus on soil health and timely actions.

• When in doubt, tap into OSU Extension guidance or talk with a local turf professional for your Ohio lawn.

A final thought

Lawns aren’t just a green canvas; they’re living systems. Grubs remind us that what happens beneath the surface—the root zone—matters just as much as what you see above ground. In Ohio, a smart blend of cultural care and thoughtful pest management helps keep turf resilient, vibrant, and ready for those long Ohio summers. If you spot signs of root trouble, you’re not alone—and with the right steps, you can steer your lawn back toward robust health.

If you’d like, I can tailor this into a region-specific guide for your county in Ohio, or translate these ideas into a simple seasonal calendar to keep on hand.