KC Gardens

Growing hordes of Japanese beetles wreak havoc on foliage

Japanese beetles have become a more common pest in recent years.
Japanese beetles have become a more common pest in recent years. UC Statewide IPM Program

Japanese beetles have been defoliating plants in the Eastern United States for years, slowly working their way west.

Starting a little more than 10 years ago, local residents would send a sample to us here at the Johnson County Extension office every couple of years. From what we could tell, there were small pockets of the beetle, mainly in areas along rail road tracks.

In 2014, we noticed a dramatic uptick in the number of samples people were sending to us. At the same time lawn services, tree care companies and other landscaping professionals began reporting more Japanese beetles than ever before. Clearly, Japanese beetles have been spreading more widely throughout the metro area each year.

The beetles are troublesome on two fronts. The adults feed on several types of plants including roses, grapes, crabapple trees, linden trees and birch trees, to name a few of the more popular targets. Its grub can feed on the roots of grass, ruining lawns.

What people usually detect are adult beetles. which are active for about six weeks during the summer. Adults are less than  1/2 -inch long, metallic green and have coppery wing covers. Their most identifying mark is white tufts of hair that protrude from the end of the abdomen. On small beetles they look like white dots.

Sometimes, identification of the Japanese beetle requires a microscope to see the hair patterns on its butt.

Adults eat the foliage of the host plant, usually in mid to late summer, which means the plant has had time to store food reserves. This means most established plants will be able to tolerate minor feeding with no loss in vigor.

So one option, when you see an infestation of Japanese Beetles is to do nothing. They often feed in clusters, so another option is to knock them off into a bucket of soapy water or alcohol to kill them.

You could also spray chemicals such as cyfluthrin or bifenthrin which are effective two to three weeks. Carbaryl (Sevin) is also effective for one to two weeks. The downside of those chemicals is they kill beneficial insects that pollinate and feed on other plant-eating pests such as spider mites.

New plants field trip

Come see the hottest and newest plants before they hit the garden centers during a field day at the K-State Research and Extension Horticulture Center at 35230 W. 135th St., Olathe.

The field day, 8 a.m.-2 p.m. Saturday, also offers a chance to talk with researchers and master gardeners about the best ways to grow them successfully. Admission is $5 and includes classes, demonstrations and cold bottled water. Lunch will be available for purchase.

University researchers have planted 600 cultivars submitted by plant and seed companies to determine what grows best in Kansas City landscapes. The Horticulture Center created a list of recommended grasses, flowers or vegetable varieties based on those results.

Field day attendees will get a chance to see what worked and what didn’t. They’ll also learn about foodscaping (incorporating vegetables and herbs into the landscape) and how to grow colorful cutting-edge flower gardens. Johnson County residents are invited to bring soil for one free test to determine nutrients in the soil. For more information, including how to take a soil sample, go to johnson.k-state.edu or call 913-715-7000.