KC Gardens

Japanese beetles have finally arrived in KC

When a horticulturist is asked, “Do we have that pest here?” many times they will reply, “Well, not yet, but it is only a matter of time.” With that thought in mind, I have been asked for years about the Japanese beetle. Japanese beetles have been defoliating plants in the eastern United States, slowly working their way west.

When I started in Extension many years ago, “Not yet” was my standard reply to the Japanese beetle question. Well time is up. We now have Japanese beetles here in Kansas City.

In the past, we would get a sample every couple of years. But this year the Johnson County Extension office has received more samples than I can remember. Professionals in the green industry also report seeing more Japanese beetles than ever before.

Japanese beetles can be troublesome on two fronts. The adults feed on a wide variety of plant materials including: rose, grape, crabapple, linden and birch, to name a few of the more popular targets. The grub can be a pest of the lawn, feeding on the roots.

What people are detecting is the adult stage, which is active for about six weeks in the summer. The adult is less than ½ inch in length, and metallic green in color with coppery wing covers. The most identifying marking is white tufts of hair that protrude from the end of the abdomen. For the average person, that means white dots on the side of the small beetle. The larvae are a white grub that looks much like the other grubs found in our area.

Identification of the Japanese beetle will require a microscope and an up-close look at the hair patterns on its butt. I am going to assume most of you will leave anal inspection to the trained professional. I can hardly wait for your sample!

Damage from the adults is defoliation of the host plant. The good news is many well established plants will be able to tolerate minor feeding with no loss in vigor. The feeding tends to be more in mid to late summer, which means the plant has had more time to store food reserves for next year.

Options for control range from doing nothing, to hand removal or chemical sprays. They often feed in clusters, so knocking the adult beetles off into a bucket of water or alcohol with kill them. Chemical sprays such as Sevin or cyfluthrin are effective and will last for up to two weeks. The disadvantage of spraying is the removal of beneficial insects from the plant that can control other pests such as spider mites.

With all that being said, it is not time to panic. Even though we are seeing more Japanese beetles, this is not a widespread outbreak. The purpose of this column is to help you learn how to properly identify Japanese beetles so that if the time arises, you will be prepared.

So ask me now if we have Japanese beetles and you will get a new answer. Yes we do, and in ever-increasing numbers. But only time will tell just how damaging their presence might be in Kansas City.