Question: I have Japanese Beetles that are damaging my roses. What is the best way to get rid of them?
Answer: Adult Japanese Beetles are very active from mid-July through August and they especially like roses. These beetles are about half-inch long and are metallic green and bronze in color. The beetles are slow and one easy way to get rid of them is by picking them off the plant by hand and dropping them into a bucket of soapy water. This is the method I use to quickly get rid of them. They usually start feeding on the top of the plant and the fact that beetles are on a plant will attract more beetles.
Several insecticides are effective against Japanese Beetles feeding on foliage. Some examples are carbaryl (Sevin) and permethrin (Astro EC). These provide about two weeks of protection and repeated applications may be needed.
The life cycle of a beetle includes a grub stage. The adult females lay eggs in mid-summer in lawns, turf and cultivated land which hatch into beetle larvae or grubs. The grubs will feed on the roots of grasses and other plants. When the soil cools in the fall, the grubs will pass the winter deep in the soil. They will then move upward in the soil in the spring to begin feeding again, complete their growth and emerge from the soil as beetles in the middle of June. Grubs are easier to control when they are small, so early August is the best time to apply insecticide to the lawn. A Purdue Extension article E-75-W “Japanese Beetles in the Urban Landscape” provides more information on recommended insecticides and control methods for the grub stage.
I used insecticides to control grubs one year. And, I’m sure that it reduced the grubs in the soil and the number of Japanese Beetles emerging from my yard the next summer. However, I later realized that beetles will travel 1 -2 miles to find the plants that they prefer. And eliminating grubs on my property doesn’t impede the growth of grubs in the surrounding neighborhood lawns. The next year, I seemed to have just as many Japanese beetles on my plants as I did before. But, my lawn was healthier!
Some folks will strongly argue for Japanese Beetle traps. These pheromone traps have scents that will attract both male and female beetles. In fact, they will lure beetles from several thousand feet away toward the traps. While the traps will catch a lot of beetles, research has shown that more beetles will fly toward the traps than are actually caught. You’ll actually be encouraging more beetles to come into your yard to feed on the plants.
Japanese Beetles are just one insect that is active at this time. The hot summer days brings out many more insects into the garden and it’s important to identify the good bugs from the bad bugs.
The Greene County Master Gardeners are hosting a class on insects that are commonly found in gardens this time of the year. Bob Bruner, an entomologist and Purdue Extension Ag & Natural Resourced Educator in Clay and Owen Counties, will be conducting the class at the Greene County Community Event Center at the 4-H fairgrounds on Thursday, Aug. 3 at 6 pm. If you are interested in learning more about garden insects, please come on out. Admission is free.
This question was answered by Lila Massa, Greene County Master gardener. Send your garden-related questions directly to the Master Gardeners. Email your question to GardenQuestions45@gmail.com or send by mail to Ask a Greene Gardener c/o Greene County Extension, 4513 SR 54, Bloomfield, IN 47424.