Theeey’re back … Japanese beetles

Ken Johnson

It’s that time of year again. Japanese beetles have begun emerging and will be around for about six weeks (mid-August). As you are probably all too aware, the adults feed on a wide variety of plants (over 300 different species). Some of their favorite plants include linden, rose, crabapple, willow, grape and raspberry. Adults will begin feeding on the upper, sunlit portions of plants and work their way down. They typically feed on the upper leaf surface, leaving the bottom leaf surface behind, but will also eat all the way through leaves. Their feeding damage can cause leaves to look lace-like; and when feeding is heavy, entire branches can be stripped of leaves. One of the reasons they are so destructive is that they are attracted to plants that have already been damaged. The beetles will also release pheromones to attract other beetles. Because of this, large numbers of beetles can be attracted to suitable plants.

There are several different things you can do to manage Japanese beetles.

  • They can be removed by hand. The best time to do this is in the early morning while they are still sluggish. Put a few inches of water in a container along with a drop or two of soap (this will help break the surface tension of the water). You can then shake or pick the beetles and put them in the bucket and drown them. This may be a great project for kids who love playing with bugs.
  • High-value plants, like roses, can be covered with cheesecloth or other fine netting during peak beetle activity to protect them, as well.
  • Japanese beetle traps are not recommended for managing populations of Japanese beetles. They attract far more beetles than they can trap and may end up doing more damage than good.
  • As a last resort, you can use chemicals to help manage the population. For many of the chemicals this will require several applications. Chemical options include: acetamiprid, befenthrin, carbaryl, cyfluthrin, imidacloprid (applied as a soil drench, should be used before May) and permethrin. When choosing a product, make sure that the site/plant to which you plan on applying it is listed on the label. Don’t apply chemicals at higher rates than are listed on the label. Just remember, always make sure to read and follow all label directions. It’s the law.
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