How to Get Rid of Scarab Beetles and Grubs

Getting rid of scarab beetles and their grubs comes down to timing, and most people get the timing wrong. The grubs feeding on your lawn roots right now hatched from eggs laid weeks or months earlier by adult beetles, and the window for effective treatment is narrower than you’d expect. Whether you go the chemical route, use biological controls like parasitic nematodes, or reshape your lawn care to make your yard less hospitable, each approach works best at a specific point in the grub life cycle. Understanding that cycle and matching your response to it is the difference between a healthy lawn and a patchy, spongy mess that peels up like carpet.

Recognizing the Problem Before It Gets Worse

Scarab beetles are a huge family, but the ones wrecking your lawn are likely Japanese beetles, masked chafers, European chafers, or June beetles. The adults of some species, like masked chafers, don’t even feed and aren’t considered pests themselves. Their larvae are the real problem. Grubs live underground, chewing through grass roots from the time they hatch until they pupate the following spring or summer.¹ Japanese beetle adults, by contrast, do feed on foliage and can skeletonize leaves on ornamental trees, with some birch varieties suffering severe damage year after year.²

The telltale sign of a grub infestation is turf that feels spongy underfoot and can be pulled up in large pieces, almost like rolling up a rug. Damage is worst in late summer and fall, when second- and third-instar larvae are largest and eating the most. Spring damage tends to be milder because cooler, wetter conditions help the grass tolerate root loss.¹ But the problem often looks worse than the grubs alone would cause, because skunks, raccoons, and birds tear up turf to get at the larvae. That secondary digging damage can be devastating even when grub densities alone wouldn’t have killed the grass.

The damage isn’t limited to lawns. In nursery and Christmas tree operations, even low grub densities cause heavy root destruction in young seedlings. Researchers found that as few as three grubs per square foot caused severe root damage to two-year-old Fraser fir seedlings, often leading to decline or death.³

Scouting and Knowing When to Act

Before you treat, you need to know whether treatment is justified. Grab a spade and cut a few one-square-foot flaps of turf in areas that look stressed, then count the grubs in the soil underneath. Research on European chafer infestations found that grubs cluster in patches, so a property’s average density can be well below the damage threshold while a specific area is getting hammered.⁴ The commonly cited action threshold for most white grub species is roughly five to ten grubs per square foot for general turf, though this varies by grass type and how well the lawn is otherwise maintained.

That same research showed that site characteristics like lawn age, shade cover, and the percentage of Kentucky bluegrass could predict whether a property was likely to have a grub problem at all. Newer lawns and sunny areas with plenty of bluegrass tended toward higher densities. If your yard fits that profile, sampling a few spots in late August or September is worth the five minutes it takes. Properties that didn’t fit the risk profile often didn’t need treatment at all, meaning a smarter scouting approach could lead to far less pesticide use overall.⁴

Cultural Practices That Reduce Grub Populations

The simplest and cheapest line of defense involves changing how you maintain your lawn. Three practices have solid research support: raising your mowing height, withholding irrigation during peak beetle flight, and, in some cases, lowering soil pH.

Mowing your lawn higher promotes deeper, denser root systems, which makes the grass more tolerant of root feeding and harder for animals to dig up. Research comparing low mowing (about two and a half inches) to high mowing (about four inches) found that a taller cut supports robust roots that need less water and fewer chemical inputs.⁵ Separately, field trials showed that high-mown turf had consistently smaller and fewer masked chafer grubs.⁶

Withholding irrigation matters because female beetles preferentially lay eggs in moist soil. In those same field trials, plots watered during beetle flight periods ended up with significantly more Japanese beetle and masked chafer grubs than plots that were left dry.⁶ If you can tolerate a slightly brown lawn for a few weeks in midsummer when adults are flying and laying eggs, you may substantially reduce the next generation of grubs. Aluminum sulfate applications to lower soil pH reduced total grub biomass in tall fescue by as much as 77% in the same study. However, soil moisture gradients could override the benefits of both mowing height and pH adjustment, so these are tools to stack together rather than silver bullets on their own.

One counterintuitive finding: organic fertilizers like composted cow manure increased populations of green June beetle grubs in some years.⁶ Green June beetle larvae feed on decaying organic matter rather than living roots, so heavy organic amendments can actually attract a different grub species entirely.

Biological Controls That Actually Work

If you want to avoid synthetic insecticides, parasitic nematodes are the strongest biological option. These microscopic roundworms seek out grubs in the soil, enter their bodies, and release bacteria that kill the host. The nematode species Steinernema scarabaei stands out as especially effective. In field trials, it provided excellent control of Japanese beetle, oriental beetle, and European chafer grubs, and it outperformed the more commonly available species Heterorhabditis bacteriophora against several grub species.⁷ It also killed grubs faster than H. bacteriophora in head-to-head field comparisons.

Research in honeysuckle fields confirmed that S. longicaudum and H. bacteriophora reduced white grub populations about as effectively as a conventional insecticide, and nematodes persisted in the soil for at least 42 days after application.⁸ Getting nematodes to work well depends on soil conditions. Their infectivity peaks at moderate soil moisture levels and drops in very wet or very dry soil. S. scarabaei is unusually hardy, remaining active across a wider moisture range than other species.⁹ Apply nematodes in the evening or on an overcast day, water them into the soil immediately, and target late summer when grubs are small and most vulnerable.

Entomopathogenic fungi are another biological option. Both Beauveria bassiana and Metarhizium anisopliae killed June beetle larvae in laboratory studies, with B. bassiana reaching nearly 80% mortality in young grubs. Older, larger grubs were harder to kill, so early application timing matters here too.¹⁰

Two biological products that get a lot of marketing attention deserve a reality check. Milky disease spore powder (Bacillus popilliae) has been sold for decades as a Japanese beetle grub control. But multi-year field trials on golf courses found that neither the traditional in vivo product nor a newer in vitro formulation was effective at actually reducing grub populations in real-world conditions.¹¹ Similarly, Bacillus thuringiensis galleriae (Btg) showed some ability to deter adult Japanese beetle feeding on leaves for a week or two, but granular Btg formulations applied to soil failed to control grubs at any instar across multiple field sites.¹² If you see these products at the garden center, know that the field evidence for grub control is weak.

Chemical Treatments and Their Timing

Chemical grub controls fall into two categories: preventive products applied before or during egg-laying, and curative products applied after grubs are already feeding. Getting this distinction right is the single most important decision if you go the chemical route.

Preventive insecticides, like chlorantraniliprole and clothianidin, are applied in late spring or early summer, before or during beetle flight. They remain active in the soil for months, killing newly hatched grubs as they begin feeding. Chlorantraniliprole in particular stands out for its favorable environmental profile. Research found it had little or no impact on predatory insects, soil invertebrates, earthworms, or decomposition rates in turfgrass, while still controlling grubs effectively.¹³ That’s a meaningful advantage over some alternatives.

Curative products like trichlorfon and carbaryl are used in late summer or early fall when you’ve confirmed an active infestation. They work fast but break down quickly, so they need to reach the grubs while the larvae are near the surface. Water the product in promptly after application.

Neonicotinoids like imidacloprid and clothianidin are effective grub killers, but their non-target effects vary. Imidacloprid caused some short-term suppression of earthworms and reduced pitfall trap catches of certain predatory beetle larvae, though ants, ground beetles, spiders, and rove beetles were largely unaffected.¹⁴ Clothianidin and clothianidin-bifenthrin premixes pose a more serious concern: they caused high mortality in ground beetles exposed to treated food, reduced parasitism by beneficial wasps, and harmed bumble bee colonies foraging on white clover in treated turf.¹⁵ The clothianidin-bifenthrin combination also slowed grass clipping decomposition and suppressed earthworm activity more than carbaryl.¹³

If you have a pollinator garden, clover-heavy lawn, or flowering plants near the treatment area, chlorantraniliprole is the safest chemical choice. It controls grubs without the documented harm to bees and beneficial insects associated with neonicotinoid-based products.

Why Japanese Beetle Traps Usually Backfire

Bag-type traps baited with floral scent and pheromone lures are one of the most popular products sold for Japanese beetle control, and one of the least effective. Research has consistently shown they make the problem worse. In controlled experiments, plants near traps suffered more defoliation than plants without traps, not less. Surrounding a plant with three traps resulted in over 90% defoliation within 30 hours.¹⁶ The traps also failed to reduce grub densities in the surrounding turf.

The reason is what researchers call “trap spillover.” The lures attract far more beetles than the traps can capture, so the excess beetles land on nearby plants and start feeding. A behavioral study confirmed that traps draw beetles in from a wide area, but many of them never enter the trap.¹⁷ If you must use a trap, place it far from any plants you care about. But for protecting a garden or landscape, traps are counterproductive.

For deterring adult Japanese beetles from specific plants, neem seed extracts are a proven option. Lab and field tests over three years showed that neem extracts successfully kept beetles off treated foliage, with untreated leaves nearby being completely destroyed while neem-treated leaves remained mostly untouched.¹⁸ Neem-based sprays are widely available at garden centers and work by making the foliage taste repulsive rather than by killing beetles on contact.

Choosing Grass That Resists Grub Damage

Your choice of turfgrass species affects both how many grubs you’ll have and how much damage they cause. Warm-season grasses like bermudagrass and zoysiagrass have a dense, woven mat of stolons and roots that grubs can feed on without the turf falling apart. These grasses also physically discourage skunks from digging. In golf course comparisons, patches of skunk-damaged cool-season turf ended abruptly at the boundary with bermudagrass or zoysiagrass, even though the warm-season grasses had statistically higher grub counts underneath.¹⁹ Tall fescue mowed at rough height also experienced almost no skunk digging despite high grub densities, likely because its deeper root system makes foraging more effort than it’s worth.

The degree of natural grub suppression from endemic soil pathogens and parasitoids doesn’t appear to change much based on grass species, so you’re not losing any built-in biological control by switching turf types. What you gain is a lawn that tolerates feeding better and doesn’t invite animal damage on top of it.¹⁹

Another approach involves endophyte-enhanced grasses. Certain turf species, particularly tall fescue and perennial ryegrass, can harbor beneficial fungi (endophytes) that live inside the grass plant and produce compounds toxic or deterrent to insects. Endophyte-infected grasses show dramatic resistance to foliage-feeding pests and modest improvements in resistance to root-feeding grubs.²⁰ They also tend to handle drought stress better, which ties back to the irrigation-reduction strategy. When shopping for grass seed, look for varieties labeled as endophyte-enhanced; these cultivars have been bred to maintain high endophyte infection rates.²¹

Insecticide Resistance Is Already on the Radar

If you rely exclusively on chemical treatments year after year, you may be setting yourself up for diminishing returns. Resistance to some insecticides has already been documented in Japanese beetle larvae, though most of the specific chemicals involved have since been banned or restricted for other reasons.²² The concern going forward is that heavy reliance on any single chemistry, including currently popular neonicotinoids, could select for resistance in local populations. Products with different modes of action provide more long-term options, especially in nursery and agricultural settings where the economic stakes of losing a chemistry are high.²³ Rotating between chemical classes and integrating biological and cultural methods is the practical response.

Range Expansion and What It Means for New Areas

Japanese beetles have been spreading for over a century since their accidental introduction to the eastern United States, and climate models suggest that trend will continue. Warming temperatures are expected to push suitable habitat northward into portions of Canada that were previously too cold, including areas of British Columbia, Saskatchewan, Manitoba, and the northern reaches of Ontario and Quebec.²⁴ In Europe, suitable range is projected to expand into Scandinavia, Ireland, and the United Kingdom. Japanese beetles have already established a foothold in northern Italy and the Azores, so European expansion is not hypothetical.

Interestingly, the same models show range contractions in parts of the southern United States and eastern Asia, where summer heat stress may become too intense for the beetles. Under a high-emissions scenario, one model projected nearly a 30% reduction in climatically suitable range within the U.S., concentrated below the 40th parallel.²⁴ If you’re in an area that hasn’t dealt with Japanese beetles before, the grub management techniques covered here may become relevant sooner than you’d expect. Homeowners in newly invaded areas tend to be caught off guard because they have no experience recognizing the signs of grub damage until the lawn is already ruined.