By Katie Drewitz, U of M Extension
Japanese beetles (Popillia japonica) have been in Minnesota since 1968, but in central Minnesota we do not tend to see them very often. Unfortunately, that trend seems to be changing. I have had several reports just this week from gardeners reporting large numbers of the invasive insect.
The Japanese beetle is incredibly distinct with its metallic green head and thorax and copper-brown wing covers. The beetle also has five white patches of hair along the abdomen. Unlike some invasive species, the Japanese Beetle is easy to spot because of its size being 1/3-1/2 inch.
While some invasive insects only attack certain species or types of plants, the adult Japanese Beetle feeds on more than 300 different plant species. These range from turf, fruits and vegetables, trees and shrubs, flowers, to field crops. Damage can be recognized on leaves by the skeletonized, lace-like appearance. The adults feed on the leaf tissue leaving behind the major veins. Petals of flowers are also eaten and will turn brown. On most mature and healthy plants, the damage is mostly cosmetic. Large trees and shrubs will survive significant feeding. Healthy flowering plants will have their blossoms ruined, but the plant is likely to survive. Young or unhealthy trees, and most fruits, vegetables, and herbs that are significantly eaten may not survive. Turf damage is mostly done by the larvae that feed on the root systems of grass.
While most damage is cosmetic, many people wish to remove the beetle from their plants and help maintain low populations. If you are dealing with a small population or yard-sized area, you should consider hand-removing the beetles and dropping them in a bucket of soapy water. Damaged leaves from adult feeding attracts more beetles to the area, so daily management will help in reducing your numbers. Do not use Japanese Beetle traps. These are often sold at garden centers and will end up attracting more beetles to your area. While the traps do capture a large number of beetles, it will attract a greater number than it traps. In the end, traps cause more harm than good.
If you are dealing with a large area, or the number of adult beetles is overwhelming, you can consider chemical controls. Depending on the plants that they are feasting on, the size of those plants, and your desire for reapplication will determine which products you use. You can find more specifics at https://extension.umn.edu/yard-and-garden-insects/japanese-beetles. Always read and follow the label instructions.
Special thanks to Jeff Hahn, Extension entomologist, and Julie Weisenhorn, Extension educator, for some of the details found in this article. For residents in Stearns, Benton, and Morrison Counties who have questions about this or any other horticulturally related topic you can reach me at (320) 255-6169 ext. 1 or firstname.lastname@example.org. Residents in all other counties please reach out to your local Extension Educator.