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Unwelcome encore for Japanese beetles

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Catherine W. Idzerda
Friday, July 17, 2009
— I’m still recovering from last year’s Japanese beetle story.

After it was published, I was denounced online, over the phone and even on the radio for allegedly saying nothing could be done about the beetles.

But that’s not what I said.

So this year, I’m going to be very explicit.

Very, very explicit.

My 40-by-40-foot garden is in an old pasture owned by my in-laws, the Fulton Township Thompsons. It’s tucked into a little valley between their farm fields. Up on the ridgeline, ancient oaks create artistic silhouettes against the sunset.

Into this perfect world come Japanese beetles.

Explicit description: “Japanese beetle adults are slightly less than one-half inch long, and are shiny, metallic green. They have coppery-brown wing covers that do not entirely cover the abdomen.

“The typical C-shape of Japanese beetle larvae is similar to other white grub species.”

From a UW Extension fact sheet written by R. Chris Williamson, turf and ornamental specialist

I’ve been a Rock Prairie Master Gardener for three years, and my training and study leads me to believe most pests can be controlled using an integrated pest management system.

The system involves prevention strategies, cultural practices, biological controls and chemicals—but only as a last resort.

One of the very few times I use pesticides is for Japanese beetles, and it makes me hate them even more.

At first, I tried integrated pest management practices, hand picking the beetles and dropping them into a Mason jar filled with soapy water.

Explicit tip: This method works only if you have a few beetles.

As the beetles began to eat my beans, my raspberries, my cutting flowers and just about everything else, I panicked and pulled out the big guns: insecticides.

Explicit information: “Several insecticides are labeled for use against adult Japanese beetles,” Williamson says.

Always, always follow the instructions. More spray isn’t always better.

I spray selectively to save my favorite plants.

Explicit tip: Spraying all plants all the time is a waste of chemicals and won’t eradicate all the Japanese beetles; it only reduces the damage to plants.

So says Mike Maddox, UW Extension and Rotary Gardens horticulture educator. He’s still recovering from last year’s story, too.

The biggest complaint about last year’s story?

I asserted that Japanese beetle traps weren’t effective. One guy called me up and, after denouncing me as an “idiot” and a “know-nothing,” invited me to his Janesville home to see the beetles in his traps.

Yes, I’m sure he caught lots of them because the beetles were coming from his yard—and everybody else’s too.

But don’t take my word for it, because apparently I’m an idiot.

Explicit information from the UW Extension: “…Traps often attract more beetles and result in subsequent damage to plants.”

Here’s something even more explicit from the entomology department at the University of Kentucky: “Research conducted at the University of Kentucky showed that the traps attract many more beetles than are actually caught. Consequently, susceptible plants along the flight path of the beetles and in the vicinity of traps are likely to suffer much more damage than if no traps are used at all.

“In most landscape situations, use of Japanese beetle traps probably will do more harm than good. If you experiment with traps, be sure to place them well away from gardens and landscape plants.”

But you can use other tactics.

Explicit tip: Biological controls against the grubs such as milky spore powder or beneficial nematodes are sometimes effective and are considered “natural.” Milky spore is a disease that kills the grubs, and parasitic nematodes attack and kill the grubs.

Research shows that “the performance of these products have been inconsistent,” according to the UW Extension.

But many long-time gardeners swear by the stuff. It’s possible that they were the “consistent” portion of the “inconsistent” group.

I’m giving it a try.

Explicit tip: Most soil insecticides provide adequate control of Japanese beetle grubs. However, one size doesn’t fit all.

The experts at a dedicated garden center are the best people to consult about your particular situation. Are the grubs eating your lawn? Is it your roses you care about or just your beans?

All the experts agree that it’s important to get the right product for your landscaping goals.

Yes, you might spend a tiny bit less at a big-box store, but you lose the expertise.

Buying a chemical you don’t need or that doesn’t work is a waste of money and hard on the earth.

Even an idiot knows that.


One way to beat Japanese beetles is to offer them a menu that doesn’t include their favorites. The U.S. Department of Agriculture listed these plants as less appetizing to Japanese beetles:


Red maple, boxwood, hickory, redbud, tulip poplar, dogwood, burning bush, forsythia, ash, holly, juniper, sweetgum, magnolia, spruce, pine, northern red oak, lilac, yew, arborvitae and hemlock.


Ageratum, columbine, dusty miller, lychnis, begonia, lily-of-the-valley, coreopsis, larkspur delphinium, foxglove, California poppy, coral bells, hosta, impatiens, forget-me-not, pachysandra, lantana, moss rose, showy sedum, nasturtium, violet, pansy and viola.

Last updated: 10:55 am Thursday, December 13, 2012

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