They are about to be among us, big time. Every June and July swarms of Japanese beetles attack all kinds of valuable plants. As they feed, female beetles release pheromones that attract additional beetles to the site.
So if you see one beetle, you can be sure more are nearby.
Adult beetles emerge in June and live for a month or so, eating flowers and foliage and leaving a lacy network of leaf veins.
They feed on many different types of plants, including crape myrtles, Japanese and Norway maples, grapes, fruit trees, and roses. They don’t go after hollies, red maples, most narrow-leafed evergreens, red oaks, and dogwoods.
After feeding, females burrow into the soil to deposit their eggs, from which beetle grubs hatch and feed on plant roots until cold weather forces them into hibernation. In the spring the grubs resume feeding and change into adult beetles. One generation occurs each year.
Because the beetles and their grubs have different life cycles, and are not active at the same time of the year, different methods are required to control them.
Controlling adult beetles
You can minimize an adult beetle infestation by picking them off by hand, or shaking the infested plant to knock them off, dropping the beetles into a bucket of soapy water.
Doing this in the morning makes it less likely that beetles will gather there later in the day to feed. But if you don’t get to it until the afternoon, the beetles will be sluggish after a day of feeding and mating, and easy to handpick or swipe into the bucket. There just might be more of them.
Chemical controls work well, but make sure that the chemical is designed to kill adult beetles, not the grubs. Before using any chemicals around vegetables, herbs or fruits, check to see how long you have to wait after the application before you can re-enter the area or resume harvesting.
Beetle traps usually make the situation worse, because traps attract beetles to the plants you want to protect, increasing the chance of damage.
Japanese beetle grubs feed on turfgrass roots from August through October, and again in April and May. Areas of dead grass appear if the number of grubs is high.
The best time to apply grub-control chemicals is in late August through early October when the grubs are feeding. But only apply these chemicals to obviously affected areas, not the entire lawn. (Getting rid of the grubs may also minimize any mole problems you may have.)
Be sure to read and understand the label of any chemical you use in the garden or around the home.
Jim Janke is an Extension Master Gardener Volunteer in Haywood County. For more information call the Haywood County Extension Center at 828-456-3575. © 2019 NC State University.