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Are you ready for Japanese beetles?

Reports have been coming in over the last week that Japanese beetles are now active. Soon their feeding will be evident. If you find Japanese beetles in your yard or garden, do you know how you will manage them?

Inspect early, inspect often

The first step in management is early detection; the sooner you find them feeding, the quicker you can deal with them and minimize their damage. Be sure to check regularly. You may not see any right away but don’t let your guard down, they could come later. Japanese beetles hatch during July and are active through August
Japanese beetle and skeletonizing damage. 
Photo: Jeff Hahn, UMN Extension

By minimizing plant damage, you also reduce the number of beetles attracted to your garden and yard. As beetles feed, the damaged leaves put out a volatile, which attracts more beetles causing them to gather in groups to munch on your plants.

Inspect your plants, especially if Japanese beetles
damaged them the last few summers. But don't automatically assume they will be a problem.  Their numbers vary from year to year so it can be hard to predict how abundant they will be.

Watch for both beetles and evidence of their feeding. Japanese beetle chewing starts as small holes. As they continue to feed, leaves become skeletonized, i.e. the leaf tissue is consumed except for the major veins.  These damaged areas eventually turn brown.

Many options to manage Japanese beetles

What should you do if you find Japanese beetles in your yard or garden? There is no one answer that fits all situations; it depends on what plants you find them on and how many you are seeing.
When you handpick your beetles, throw
them into soapy water to make sure they
are dead.  Photo:  Jeff Hahn, UMN Extension

If you are finding them on just a few small plants, handpicking them is a good option. Keep in mind that Japanese beetles are present all summer so be sure to do it regularly. Under some circumstances, fabric barriers can also be an effective management tactic.

If you find them on a large tree, it may not be necessary to do anything. Healthy, mature trees and shrubs tolerate Japanese beetle feeding in a year; any damage usually just affects the appearance. However, trees are more likely to be damaged if they are recently transplanted, unhealthy, or have been severely defoliated several consecutive years.

If you are looking for a pesticide to protect your plants, there are a variety of residual insecticides available to help protect them. Pyrethrins, neem oil, and Bacillus thuringiensis galleriae are low risk products.
Trees can usually tolerate feeding without any
lasting injury.  Photo: Jeff Hahn, UMN Extension

Always be sure the plant you are intending to treat is on the label of the pesticide you are using. Also, observe any restrictions concerning pollinators. When treating fruits or vegetables, make sure to observe the number of days between application and when you can harvest your crops.

Not all management options are effective. Don’t
use Japanese beetle traps. Research shows they are not effective in home gardens. It is not unusual to have more damage using them than without them.

For more information, see Japanese beetles in yards and gardens.

Author: Jeffrey Hahn, Extension Entomologist
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