beautiful hydrangeas

We need to talk about Japanese beetles

Hello, everyone and thank you for coming. We’ve asked you here today because we need to talk to you about something shiny, green, and annoying. Yes, you guessed it, we need to talk about Japanese beetles. 

No doubt, many gardeners have noticed the return of this pest over the last few weeks. Right when our gardens are looking really fantastic, they swoop in to spoil the show. At the height of their activity, the metallic green menaces are hard to miss. They congregate in large numbers to breed, feed, and fly around quite clumsily. Damage from feeding typically shows up as lacy, skeletonized leaves and damaged flowers. What’s more delightful, excrement will be evident if they have been feeding particularly voraciously on a favorite plant.

What to Do about Japanese Beetles

If you have a heavy population of Japanese beetles in your area, the number one recommendation is to choose plants that they don’t favor. Many of the best landscape trees, shrubs, and perennials are either ignored by them or only very lightly damaged. Viburnum, dogwood, spirea, hydrangea, lilac, dwarf bush honeysuckle, dogwood, evergreens, loads of perennials, many maples and oaks, ginkgo, hackberry, musclewood, and ironwood all excellent choices for a Japanese beetle resistant landscape. This is only a short list- there are many more.

The Good News

Though the prognosis might seem grim for plants that the beetles love, there are a few pieces of good news in all this:

  • Nature is trying to help! A parasitic fly called Istocheta aldrichi (catchy name, no?) lays eggs on Japanese beetle’s heads. If you find a beetle with a white dot on its head, let that one live to help proliferate these predators. We found a beetle with this white dot just last week! Here’s a link with more information on how to attract these beneficials and helpful pictures.
  • In most cases, mature, vigorous plants can sustain heavy Japanese beetle feeding and shrug it off, so try not to panic. Light damage is not an issue at all.
  • The heaviest feeding period is a relatively short window. Accepting some damage or controlling light infestations before they get out of hand is the best call. 

When to Act

Defoliation of immature, unhealthy, and newly installed plants can be a cause for concern and there are different treatment options available. If you’re dealing with a smaller tree or shrub, you can even knock the beetles into a bucket of soapy water by hand. Works like a charm!

If you live in an area with a high Japanese beetle population and many of the plants in your landscape happen to be delicacies, it might be time to consider some replacements. We are happy to point you toward the plants that we have noticed display greater resistance. You might even consider replacing some of your lawn, since turf is the preferred breeding ground for these pests. 

Whatever you decide to do, remember that these beetles are a terrible annoyance but they’re not the end of the world. Most plants are equipped to deal with some herbivory, and many resistant plants are available.  

Want more information? Here’s a link to the University of Minnesota recommendations

 

2 thoughts on “We need to talk about Japanese beetles”

  1. Simone, we love you articles. Maybe I’m to aggressive: I use Japanese beetle traps and at least I have the personal satisfaction of eradicating thousands of them. I also use grub control on ma yard. Yes, I still have them this year, but it seems like I have fewer. Maybe I just tell myself that to make me feel better.

  2. Thank you! It certainly is a satisfying feeling to control them. The Minnesota Landscape Arboretum recently posted on their Facebook page that they found several with white dots on their heads. Wonderful news!

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