Skip to content

On the Lookout for Japanese Beetles

It’s that time of year where every trip to the garden involves an inspection for Japanese beetles. Are they here yet?

So far, in my garden in St. Paul, the answer is no, not yet. Japanese beetles typically appear in Minnesota in late June or early July. They live for 6 to 8 weeks, creating havoc the entire time, eating roses, green beans, birch trees and about 300 other plants. They mate; the grubs hide in the soil for the winter, and it’s all over before the Minnesota State Fair.

Japanese beetle on rose

Roses are a favorite target of Japanese beetles.

While beetles have been in the United States more than 100 years, they have only been in Minnesota about 50. In 2018, we first spotted them on June 26. In 2017, the first sighting (for me) of Japanese beetles was not until July 3. In 2015, they were here by June 24. I’ve seen none so far.

We’ve had a cool, wet spring, so perhaps they are delayed. Many gardeners are hoping that the brutal winter we had with early sub-zero temperatures and a lengthy cold period may have knocked them back, but conversations with University of Minnesota entomologists indicate that is unlikely. We did have a tough winter, but beetle grubs stay below ground—sometimes as low as 6 to 8 inches below ground.

In addition, going into the winter of 2018/2019, Japanese beetle grub numbers were high. The U has a research area in Rosemount where researchers counted 26 Japanese beetle grubs per foot. That’s a lot. Grub numbers are most affected by drought during the mating season.

Dealing with Japanese Beetles

Once they get here, beetles are a real challenge. Keep an eye out for the Japanese beetles because early interventions tend to be more successful.

Traps do catch a lot of beetles, but they also bring more into your yard. They are not recommended unless you have a very large yard and can set the trap away from your garden. The best non-insecticidal control is to knock the beetles into a bucket of soapy water. Going out in the morning is best as they tend to be out and they move more slowly then. You can also add covers to plants you want to protect. Fruit plants, however, should not be covered until blooming is finished and no pollination is required. Insecticides can work, but the effective ones tend to harm bees as well. This article from the University of Minnesota Extension covers your options and the pros and cons of each.

A long term option may be to not plant the plants JBs love the most, such as roses and grapes. It also helps to remember that this, too, shall pass, and most plants are not killed by Japanese beetles.

 

5 Comments

  1. Henry Fieldseth on June 28, 2019 at 11:30 am

    No need for soap in the water. Since I feed them to the chickens, I did not want to use soap. I knock them into plain water which completely contains them. The soap might kill them but I prefer the free chicken feed. A cut-flower farm nearby does the same and saves them for us!

    • Mary Lahr Schier on June 30, 2019 at 2:36 pm

      Thanks for the comment, Henry. I have heard that chickens love the JBs.

  2. Christine Yesko on July 20, 2019 at 12:41 am

    I too use a bucket with only water. It seems that they are attracted to the white bucket, I just place the bucket close to my flowers and they fly in and drown. Have done this many years and have killed lots of beetles.

  3. Paul Mencke on July 21, 2019 at 8:27 pm

    I cut a small hole in the bottom of the JB trap bag and suspend one over my koi pond and one out in my lake in one foot deep water on a shepherd’s hook. The koi and sunfish love to eat them when they drop out of the bag.

    • Mary Lahr Schier on July 21, 2019 at 9:24 pm

      Great idea!

Leave a Comment