A species of scarab beetle, these iridescent insects can be a nightmare for gardeners. Japanese beetles or Popillia japonica skeletonize the leaves of many plant species leaving just the veins. As the females eat throughout the early summer they lay eggs in the ground, eventually producing 40-60. Around midsummer, these eggs hatch into larvae which feed on grass roots until fall when they burrow 4-8 inches into the ground and go dormant for winter. In late spring they become pupae and eventually beetles which emerge from the soil and begin the cycle anew.
If you struggled with Japanese beetles in your garden this summer, fall is the perfect time of year to take care of them. Here are a few ways you can control Japanese beetles in your garden.
Beneficial nematodes or Steinernema feltiae are worm-like parasites that move through the soil and feed on Japanese beetle and other larvae. When beetles are in their larvae stage spreading nematodes on your lawn or around your fruit trees and garden can be effective.
Milky spore or Bacillus popilliae is a bacteria that attacks Japanese beetles in their larval stage. It can be spread on lawns and gardens. Apply before the ground freezes.
If you have chickens giving them free rein of the garden or around fruit trees during fall and winter can help. Chickens actively forage for insects in the soil. While their incessant scratching can be a problem around your plants in the middle of summer it can be extremely helpful in the fall. They’ll dig up and eat the larvae. During the summer they’ll also enjoy eating the beetles but you’ll want to limit their time in the garden and fence off small plants that can be easily damaged.
If free-ranging your chickens even for a bit isn’t an option for you, consider putting up moveable fencing. A plastic deer netting will work in a pinch or you can invest in something electric netting which is easy to move, allowing you to rotate your chickens’ pasture.
Some studies (like this one from 2015), have indicated that wildflower plantings can increase insect biodiversity and the number of beneficial insects in gardens and reduce pest issues.
Floating Row Cover
While not necessarily the easiest solution, adult Japanese beetles can also be kept at bay with floating row cover.
Some folks have also had success using neem oil to protect plants from adult beetles. It’s an organic pesticide and fungicide that’s used for a variety of garden problems and is available in many garden supply stores. It’s generally sprayed directly onto the plant. Multiple applications may be necessary throughout the season.
Crop Rotation & Cover Cropping
As always we recommend keeping your soil and therefore plants healthy by employing crop rotation and cover crops. Healthy plants are much less susceptible to pest problems. Fall is the perfect time of year for a soil test as well.