How to Control Japanese Beetles
A Japanese beetle, feasting on tender, new leaves of a rose bush. Photo: David Grist
JAPANESE beetle damage is pretty easy to identify. Usually, the bugs can be caught in the act. The telltale signs of Japanese beetles include skeletonized leaves or total defoliation. Japanese beetles also love to eat rosebuds — from the inside out. Keep in mind that Japanese beetles are seldom found west of the Mississippi River, but chances are good that they're headed your way.
The beetles are strangely beautiful: roughly 3/8-inch long and 1/4-inch wide. They have shiny, metallic-green bodies and copper-colored wing covers.
Five Ways to Control
Pyrethrin-based insecticide is a safe and effective way to control these pests on vegetables, grapes, raspberries, flowers, roses, trees and shrubs. In addition to controlling Japanese beetles, it also controls cucumber beetles, flea beetles, cabbageworms, Colorado potato beetles, and more.
Neem Oil Concentrate works on a wide variety of pests including Japanese beetles, aphids, mites, whiteflies, flea beetles and earwigs.
Neem oil comes from a tree; when sprayed on plants, it reduces feeding. Scientists call it an antifeedant. Important: neem works best when applications begin at first sign of attack.
Hand Pick: Japanese beetles are slow. You can easily pick them off plants with your hands and toss them into a bucket of soapy water. Do it in the morning when the beetles are less alert.
Prevent: Although the following solutions won't provide immediate gratification, you will be better off next year. Grub Guard kills the grubs that turn into Japanese beetles. Ideally, apply it in spring before the beetles emerge. The second half of this 1-2 prevention punch is Milky Spore, which also kills grubs. It takes a year or so to get established in your soil, but it keeps working for 10 years or more.
Trap: A Japanese beetle trap is recommended only if you have a large yard, and can place the trap away from your garden. If you have a small yard, you'll just be telling the beetles, "The party's at my house!" If you use a trap, put it out for a day or two at a time every couple of weeks.
Why Neem Oil?
Not only does it control Japanese beetles in the heat of their feeding frenzy, it also controls: adelgids, wooly adelgids, sawflies, aphids, sawfly larvae, cabbage loopers, lacebugs, scale, cabbageworm, leafhoppers, chinch bugs, mealybugs, spider mites, crickets, earwigs, flea beetles, mole crickets, squash bugs, pear slugs, tent caterpillars, grasshoppers, pear psyllas, thrips, green stink bugs, whiteflies, psyllids, gypsy moth caterpillars, rose slugs, harlequin bugs, rust mites and other soft-bodied insects.
Neem can also be used on roses in a formulation called Rose Rx, which prevents diseases that plague roses: blackspot, powdery mildew, rust, scab, anthracnose and more.
Even if you use Milky Spore and Grub Guard, you can still get Japanese beetles. Yes, they’re slow, but they can fly up to a mile for a good meal. Neem or pyrethrin-based sprays can control these outbreaks.
If you have these plants, monitor them closely:
- Japanese maple
- Norway maple
- Crape myrtle
- Pin oak
- Cherry (plum, apricot, peach)