Japanese Beetle Management Tips

Japanese Beetle Management Tips

Japanese beetles are a pest—not just by definition—but the damage they can cause to plants. PJ Liesch, known as the Wisconsin Bug Guy on Twitter, is an entomologist at the University of Wisconsin-Madison and Insect Diagnostic Lab. He explains how you can identify the beetles.

“They’re a type of small scarab beetle. They have a very distinctive coloration with some metallic shiny green on their body, although their wing covers, those are a coppery brownish bronze color, and then on the side of the body are a series of little puffs of whitish hair running down the side of the abdomen.” 

Liesch says managing the beetles depends on the scale you are managing. It’s different for home gardeners versus cropland.

“On the perspective of a home gardener or a yard where we have some trees or shrubs that are effected, one option is to actually go out and handpick the beetles, you could squish them by hand, you could carry a little container soapy water and knock the beetles into that, that approach can be very labor intensive. We do also have some other approaches in home yards. One thing I will mention, if you go to the hardware store, you may see these, the Japanese beetle traps, and it turns out from a number of research projects that if you have a trap near your plants you end up in general seeing more damaged, they seem to do more harm than good.” 

And for farmers, they should scout and keep an eye on populations.

“We do have some established thresholds for Japanese beetles, this would be the point where it makes economic sense to intervene and spray for them. If they’re lower than that level, then it doesn’t make sense to do that because we’re not getting as much benefit. And we have different thresholds out there for different crops like soybeans, for example, where they can feed on the foliage of the beans, it’s either going to be about 20 to 30 percent defoliation, depending on the growth stage of the beans. If we’re talking about corn, our main concern is the Japanese beetles actually clipping off the silks, and if they do that it’s going to disrupt pollination and we won’t get kernel development inside our ears.” 

Bottom line, he says is to scout often and be prepared to take action if needed.