What are some effective methods to reduce the Japanese beetle population?


The Japanese beetle population my large perennial beds has been increasing greatly every year despite hand-picking and using Captain Jack’s Deadbug Brew Spray (sparingly and in the evening, as I’m concerned about harming bees). Are there other methods that would be more effective and/or also reduce the population? 


Jonathan Foster, Community Education Assistant

I’m sorry to hear about your Japanese beetle woes, but rest assured you are in good company with this particular pest.

The silver lining is that while the cosmetic damage can be quite irritating, especially on nice, showy plants, the plants themselves should weather the problem well as long as the infestation doesn’t get out of hand. So overall plant health is less of a concern. But that may be small comfort if your lovely plants are looking tattered!

The easiest and least toxic method of control is simply to knock them off the leaves into a bucket of soapy water every day or two while the population persists. If they tend to fall into grass below and disappear (they let go pretty easily when bothered), or if you don’t relish handling dozens of beetles, you can spread a tarp out under the vines and gently work the foliage with a soft broom or use a hand vacuum to suck them right off the leaves.

I’ll include some Extension resources on management of Japanese beetles and their life cycle. They are an annual nuisance for many plants and the best way to mitigate the problem other than mechanical removal from the leaves is to address their grubs overwintering in nearby lawns. If the grub population can be reduced, you should notice a drop in the attendant mature beetles, as well.

UMaine Japanese Beetle Fact Sheet

University of New Hampshire Japanese Beetle Fact Sheet

UMaine Japanese Beetle Life Cycle and Management