In gardens across Minnesota, the battle against beetles begins
Published 12:25 PM Tuesday, July 9, 2024
An invasive Japanese beetle climbs up a rose bush in the Twin Cities last week. Andrew Krueger/MPR News
By Andrew Krueger, MPR News
While many Minnesotans have been plagued by mosquitoes and ticks over the past few months, another pesky insect is now beginning to make its way into yards and fields across much of the state.
Dressed in metallic green and copper hues, the Japanese beetles begin their annual feast on roses, grape vines, fruit trees and a variety of other plants, including soybeans and some other crops.
The invasive insects — first found in the U.S. in 1916, and first spotted in Minnesota in 1968 — spent last winter underground as larvae, gnawing on grass roots. Now they’re emerging as adult beetles and causing headaches above ground.
The beetles “skeletonize leaves by feeding on tissue between the major veins, giving them a lace-like appearance,” the University of Minnesota Extension reports. They also eat the blossoms and blooms of rose bushes and some other flowering plants.
July and August are the months with the most Japanese beetles. Also for gardeners who try all sorts of methods to keep the insects under control, these are the months with the most activity.
Are they harmful to the plants?
According to the U of M Extension, while the beetles can cause unsightly damage to leaves and flowers, healthy plants can survive an infestation without long-term effects.
But young plants, or plants that are already under stress – such as many plants due to the drought of recent years – are less able to withstand the attack.
And whether it’s healthy or not, if beetles target vegetable plants or fruit trees, it can reduce their yield.
And once the beetles lay their eggs underground this summer, the larvae that hatch begin to feed on the roots and can cause damage to the lawn.
Where in Minnesota are the beetles found?
The Minnesota Department of Agriculture has created a map showing where the beetles have been found in the state, including areas where they are most common.
Parts of Minnesota where pests are common include the Twin Cities and areas near Mankato, Owatonna, Albert Lea, Rochester and Winona.
No invasive insects have yet been observed in southwestern, northwestern, and northeastern Minnesota.
According to the U.S. Department of Agriculture, the beetles are widespread in most eastern U.S. states, except Minnesota. They have not yet been reported in states west of the Rocky Mountains.
What can be done to stop this?
The University of Minnesota Extension outlines several options for controlling Japanese beetles.
For smaller gardens, a common and simple method is to manually remove the beetles from plants or to knock them off and place them in a bucket of soapy water to kill them. The beetles have some fairly effective defense mechanisms—they will drop a plant at the slightest vibration of a leaf or stem—so it may take some trial and error to find an effective removal technique.
It is important to start early, when the first beetles are already visible. When beetles are active, they attract more insects to a certain area.
Japanese beetle traps can be found in stores, but U of M experts advise against them because they can attract more beetles to an area than they catch, potentially causing more damage to nearby gardens. The Star Tribune reported earlier this year that two U of M students are working on an improved trap that could alleviate some of those concerns.
Insecticides are another option, but carry the risk of harming other insects, including beneficial pollinators.
The U of M Extension reports that a wasp and a fly species have been released in Minnesota that prey on the beetles or their larvae, although “neither are very numerous and they have little impact on Japanese beetle populations.”
Another control option is to choose plants over time that the beetles do not target. And there is always the option to just live with the beetles and the damage they cause.
Do you have a favorite, proven method for dealing with Japanese beetles that you’d like to share? Email more information to [email protected] ; if we get enough submissions, we’ll collect those ideas in a follow-up post.
