How does your garden grow? Japanese beetle a pesty summer visitor

Japanese beetles for How does your garden grow column in DeKalb.

Just when your garden is beginning to produce beautiful roses and sweet juicy raspberries, those pesky Japanese beetles come along and make a mess of everything.

These beetles originally came to North America in 1916, by hitching a ride on imported ornamental plants from Japan. Japanese beetles are actually quite beautiful with their shiny, metallic-green-colored bodies that are 1/3 to 1/2 inch in length.

Japanese beetles start as turf grubs. You even may have found a few grubs when putting in your spring annuals. In northern Illinois, they live in the soil for about 10 months, and emerge from mid-June to early July. While in the soil, they feed on the roots of grasses, vegetables and ornamental plants. Once they emerge, they go after leaves, flowers and fruits. The list of plants includes over 300 trees, shrubs, fruits and vegetables. Some of their local favorites include grapes, raspberries, rose, crab apple, blackberry, linden and willow.

What can you do? Let’s start with what you should not do. It is important to not use Japanese beetle traps as a method of control. These traps contain a scent to lure the male beetles into the trap, but this actually will cause more beetles to show up in your neighborhood.

If you have a light infestation, try brushing the beetles off into a bucket of soapy water. They move pretty slowly, especially in the morning, and with their shiny green bodies, they are pretty easy to spot. This is the safest method of control.

However, if the 50-foot linden tree in front of your home is getting defoliated, then an insecticide might be called for. While the beetles usually won’t kill a healthy tree, the damage they cause can be noticeable for the remainder of the summer. There are many insecticides labeled to control Japanese beetles, just make sure to follow the label directions closely.

For those who want to use a more natural insecticide, Neem oil can be used, but it only lasts about three to four days.

You also may have thought treating your lawn for grubs would help reduce the number of beetles you get on your plants, but, while this method may help your lawn, research has shown it has little effect on controlling beetles accessing your trees and bushes, because Japanese beetles can fly long distances.

To avoid the issue altogether, you might consider landscaping that Japanese beetles don’t like, such as begonia, holly, dogwood, forsythia, columbine, impatiens, lilacs, hosta and violets, but also take into consideration your yard and the other pests you may need to battle. As an example in my yard, the deer really like hosta.

For more information on Japanese beetles, go to the University of Illinois Extension website: You also can contact the DeKalb County Master Gardeners Extension by emailing or calling 815-758-8194.

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