Are Japanese Beetle Numbers Down?

Maybe I’m imagining it, but are Japanese beetle numbers down this year?

Japanese beetles may be one of the most hated pests of northern gardeners, closely following deer in many places. While they are not prevalent all over Minnesota, Japanese beetles are “abundant” in the seven county metro area, as well as in Blue Earth, Freeborn, Steele, Omstead and Winona counties. They have been confirmed in most counties from southeastern Minnesota up through the central part of the state to the Fargo area. Check out this great map from the Minnesota Department of Agriculture to see how prevalent they are in your area.

The beetles have been around Minnesota for about 50 years. They arrived in the United States more than 100 years ago, when beetle larvae stowed away on a ship from Japan carrying  iris bulbs before imported goods where routinely inspected. They continue to thrive here in part because they are not picky eaters. They love roses, grapes, linden trees, birch trees and green bean plants, but I’ve seen them on anise hyssop, tomatoes, hydrangeas and just about every other plant in my backyard. The second reason they have persisted here is they reproduce like crazy. One thing that can interrupt their reproduction is a drought around mating time.

However, 2019 was a very wet year — the wettest ever — so that’s unlikely to have caused any drop in numbers. There were some very cold days in November and early December, before the snow arrived to protect the Japanese beetle grubs underground. Whether Japanese beetle numbers are down or up, the methods for dealing the them are the same.

Get Them Early and Often

The least harmful way to deal with Japanese beetles, especially if their numbers are down, is to hand pick them and dump them in a bucket of water. You can add dish soap to it, if you’d like. They are easiest to grab in early morning. Beetle traps do work in attracting the beetles, but be warned, they attract a lot of beetles. (A trap at your neighbor’s house may be the best solution!)

There are a variety of ways to treat the grubs in your lawn and the University of Minnesota Extension has a great fact sheet on Japanese beetles that addresses the pros and cons of all of these methods. If you have a severe beetle problem, it’s definitely worth reading.

What about in your garden? Are the Japanese beetle numbers down in your area?