A large topic of conversation surrounding the Victory Memorial Drive has been the large patches of dry, brown and dying grass, most near trees. There has been a lot of speculation about what is causing this, especially since it is also appearing in some community home lawns. Some thoughts have been ants, drifting herbicides or animals, but I think the most likely explanation is grubs of the European Chafer Beetle. A fellow Master Gardner in our community plucked a grub from some of the infected turf, took a picture and sent it to the Minnesota Department of Agriculture (MDA) for verification. As of this writing she has not heard back yet, and she is preserving the critter in alcohol in case they need to have a closer look. The MDA needs to track and learn more about the European Chafer Beetle in Minnesota. It is a serious threat to turf growers and golf courses (and thus our economy) and of course home lawns.
The European Chafer Beetle was only discovered in Minnesota, in a lawn in south Minneapolis, in August 2020. It first appeared in a nursery in Rochester, New York in 1940 and from there it migrated to New Jersey, Connecticut, Massachusetts, Rhode Island, Ohio, Delaware and the lower peninsula of Michigan. It showed up in Door County, Wisconsin in 2016 and now has raised its ugly head in Minnesota.
The mature European Chafer is about ½ inch long and tannish to red in color. It resembles a June bug but is smaller and lighter in color. The adults emerge from the soil in mid-June to early July around dusk on warm clear evenings to mate around shrubs and small trees, and then return to the soil. This makes their activity hard to detect. Their mating activity is temperature dependent and not all of them emerge at once.
The adult chafers are not the problem, they do not eat at all. After mating they lay their eggs in the top two-four inches of the soil and these eggs generally hatch within two to three weeks. It is the larvae they leave in the soil that feeds on the turfgrass roots; they can do much more damage than Japanese beetle grubs because they spend a larger portion of summer feeding on turfgrass roots.
The grubs (larvae) over-winter in the soil just below the frost line. As the ground thaws in spring they return closer to the surface and continue to feed. In late spring and early summer they descend back in the soil to pupate and then emerge as the adult beetles ready to repeat the cycle. So what we may be dealing with right now are the grubs that were laid by the beetles last summer.
The European Chafer grubs are ¼ to 1 inch, C-shaped with a dark brown head and obvious legs. The larva is very similar to Japanese and May/June Bug beetles and may require an entomologist to identify – which is where the MDA comes in. If you think you have a European Chafer either adult or larva, you are asked to alert the MDA through their Arrest the Pest website: mda.state.mn.us/plants-insects/arrest-pest or call 1-888-545-6684. Before doing so try to capture the insect or grub, take a picture and put it in a baggie in the freezer, as my colleague did. You will be contacted by the MDA if they want to see your specimen.
So what kind of treatment can you use if it is confirmed that you have the European Chafer plaguing your home lawn. Since it is relatively new in Minnesota we can turn to our neighbor, Wisconsin, who has been dealing with this pest since 2016. According to the University of Wisconsin Extension website, insecticides are the main way to deal with grubs. Not all insecticides will work and even those which are effective won’t work if applied at the wrong time.
There are two types of insecticides; preventatives and curatives. The best time to apply a preventative insecticide is when the grubs are small. The window of opportunity is the time between egg laying and hatching. Since it is hard to know when the beetles are actively mating and laying eggs, mid-July is suggested as the best time for a preventative insecticide application. And since not all of the eggs are laid and hatched at the same time a curative insecticide should be applied in late August to early September to kill the larva that escaped the first insecticide. More information on the types of insecticides and how to apply them can be found in the “Controlling European Chafer in the Summer Months” bulletin on the UW Extension website extension.wisc.edu.