Getting rid of green june beetles requires a two-pronged approach: targeting the grubs living in your soil and managing the adults buzzing around your yard and garden. Timing matters more than anything else with these insects, because the window for effective grub treatment is narrow. Here’s how to handle both life stages.
Why Timing Is Everything
Green june beetle grubs hatch in late July and feed aggressively from August through late October, growing to about three-quarters of an inch long before burrowing deeper into the soil for winter. In spring, they resume feeding until mid-May, then pupate. Adults emerge in summer, mate, and lay eggs in soil with plenty of organic matter, starting the cycle again.
This lifecycle creates two distinct treatment windows. You can apply preventive products before or just after eggs hatch, or you can apply curative treatments in late summer when grubs are small and feeding near the surface. Miss both windows and you’re stuck waiting for the next cycle.
Preventive Grub Treatments
Preventive insecticides work best when applied before grubs hatch or while they’re still tiny. Products containing imidacloprid, thiamethoxam, or clothianidin should go down in June or July. Applying too early (spring) gives the chemical time to degrade or leach through the soil before grubs arrive. Applying after mid-August is often too late, as the grubs may already be large enough to resist these products.
One exception: chlorantraniliprole works best when applied earlier, ideally in April or May. It takes longer to move through the soil to where grubs will eventually feed, so earlier applications actually outperform later ones. Water any preventive product in with about half an inch of irrigation immediately after application to push it into the root zone.
Curative Treatments for Active Grubs
If grubs are already in your lawn and causing damage, August and September are the best months for curative treatment. The grubs are still small, feeding near the surface, and vulnerable. Contact insecticides like carbaryl work differently from preventive products. Do not water these in after application. Green june beetle grubs have an unusual habit of crawling to the soil surface at night, so you want the product sitting on top where they’ll encounter it. Apply late in the day for this reason.
One thing to expect: curative applications often leave dead grubs on the turf surface. This is normal and actually a sign the treatment is working. You can rake them up or let them decompose.
Do not bother applying curative insecticides in spring after mid-May. Grubs stop feeding in late May as they prepare to pupate, so the chemicals won’t reach them effectively.
Beneficial Nematodes as a Biological Option
If you prefer to skip synthetic insecticides, parasitic nematodes are a proven biological control. The species you want is Heterorhabditis bacteriophora (sold as “Hb nematodes” by most suppliers). These microscopic worms hunt down grubs in the soil, infect them with bacteria, and kill them within a few days. Field trials have shown at least 70% reduction in pest populations when applied correctly.
The application rate matters: you need a minimum of about 24,000 nematodes per square foot. Most commercial products are sold in quantities that make this easy to calculate. Nematodes can be applied anytime grubs are present in the top few inches of soil, roughly April through October, but late summer applications tend to be most effective.
Soil moisture is critical. Nematodes dry out and die quickly on dry ground, so water your lawn before and after application, and keep the soil moist for at least two weeks afterward. Sandy soils dry out faster and need more frequent irrigation. Heavy clay soils can make it harder for nematodes to move through the ground, reducing their effectiveness. Overcast days or evening applications give nematodes the best chance of survival, since UV light kills them.
What About Milky Spore?
Milky spore disease is a popular biological control for lawn grubs, but it only works on Japanese beetles. The commercially available strain is exclusive to that one species. If your problem is green june beetles, milky spore will do nothing. This is a common and expensive mistake, so make sure you’ve correctly identified your grub species before buying. Green june beetle grubs are easy to spot: they crawl on their backs, which is unique among common lawn grubs.
Managing Adult Beetles
Adult green june beetles are the large, metallic green insects you see flying low over lawns in summer or swarming ripe fruit. They’re clumsy fliers and easy to catch by hand, which is actually a practical control method if your infestation is moderate. Early morning, when beetles are sluggish, is the easiest time to pick them off plants.
For fruit trees and garden plants, a bucket of soapy water works well. Knock or shake beetles off branches into the bucket. The soap breaks the surface tension so they can’t escape. You can also set out shallow containers of fermenting fruit juice as simple traps, since the beetles are strongly attracted to ripe and overripe fruit. Position traps away from the plants you’re protecting so you draw beetles in the opposite direction.
Covering ripening fruit with fine mesh netting or individual fruit bags prevents adults from feeding on your harvest. This won’t reduce the beetle population, but it protects the crop you care about while other control methods work on the grubs underground.
Lawn Care Practices That Help
Female green june beetles prefer to lay eggs in soil rich in organic matter, particularly lawns with thick thatch layers or heavily composted garden beds. Reducing thatch through core aeration makes your lawn less attractive for egg-laying. Aerate in fall after treating for grubs to get the double benefit of thatch reduction and improved turf recovery.
Avoiding excessive irrigation during peak adult flight (June and July in most regions) can also discourage egg-laying, since females seek moist soil. This doesn’t mean letting your lawn die, but cutting back to deeper, less frequent watering rather than daily light sprinkles can make your turf a less appealing nursery. Healthy, dense turf also recovers faster from any grub damage that does occur, so proper fertilization and mowing height for your grass type are worth maintaining throughout the season.