Kyle Geissler talks with Janesville Gazette reporter Cathy Idzerda about effective ways to battle the Japanese beetle.
Japanese beetles seem to be back with vengeance this summer. But trying to kill all the beetles in your yard could be a costly—and fruitless—endeavor.
JANESVILLE — Stop right there.
Do not buy that Japanese beetle trap.
Do not run through your yard willy-nilly, spraying everything in sight with pesticide.
Do not buy bags of mystery granules, bottles of special beetle killer or any other new fangled gizmo that promises to keep your yard free of those #*?! beetles moving through your yard like it’s an all-you-can-eat buffet.
Before you do anything, it’s crucial you understand the difference between a psychological victory and a genuine victory.
And here to tell us the difference—and give us the key to beetle control—is garden realist Mike Maddox.
Maddox, who is horticulture educator for Rotary Gardens and Rock County Extension, explained that some products and techniques give gardeners and homeowners a psychological victory—a satisfying sense they’re winning the war. But often, those techniques can make matters worse, cost a lot of money and needlessly poison the environment.
What’s needed is a genuine victory.
But first, the basics:
Japanese beetles are slightly less than a half inch long and are a shiny metallic green, said UW Extension turf and ornamental specialist Chris Williamson.
They have coppery-brown wing covers that do not entirely cover their abdomens. Newly hatched larvae are a translucent creamy white and, once feeding begins, their hindguts turn gray to black.
The grubs feed on the roots of grass and ornamentals.
Now for the specifics of what works and what doesn’t:
-- Japanese beetle traps. The traps have become increasingly popular because they give people a psychological victory. Jane Homeowner finds her trap full of dead beetles and thinks she’s making a difference.
But here’s the problem:
“They’re only catching a percentage of what they’re attracting,” Maddox said.
University studies have shown again and again that the traps bring in more beetles than they actually kill. Those extra beetles are mating and laying eggs in your lawn so that next year you’ll have a new crop of beetles and, possibly, new damage to your grass.
Now, if you have a “couple of acres” and want to put the traps on the back of the property, they’ll probably lure the beetles away from the ornamentals near your home, Maddox said.
-- Pesticides. A variety of pesticides are labeled for use against the adult beetles.
“Controlling Japanese beetles requires a defensive approach,” Maddox said.
That means protecting specific plants or trees—instead of trying to kill every beetle in the solar system.
Why?
“The beetles will just fly in from elsewhere,” Maddox said.
That is especially true in city neighborhoods.
Only spray where the beetles are present and follow product instructions to the letter.
“Some people have noticed that the beetles tend not to return to something that’s been sprayed; it becomes unpalatable,” Maddox said.
However, no specific research has proven that phenomenon—only anecdotal evidence is available.
If you don’t have a significant number of beetles, consider handpicking the beetles and dropping them into a jar of soapy water. Beetles are attracted to beetles, so such a method only works when the populations are low.
-- Systemic pesticide treatment for trees or treatment for lawn grubs.
The systemic treatment for trees is usually applied in the fall and is absorbed by the tree’s roots and helps it withstand beetle attack next year.
It’s a good defensive approach for next year, especially on valuable ornamentals, Maddox said.
Japanese beetles lay their eggs in the lawn, and grubs feed on the roots of the grass. If present in large enough numbers, the grubs can leave large brown patches on the lawn.
“Use the grub control if the grubs are killing your grass,” Maddox said.
Again, the temptation is to try to wipe out all the grubs in your lawn, even if they aren’t causing problems.
“You can kill all the grubs, but the adult beetles will just fly in from elsewhere,” Maddox repeated, this time sounding a little exasperated.
-- Other methods. Biological controls such as milky spore disease and nematodes are marketed as “natural” ways to control the grubs. Although many gardeners swear by such methods, university research has shown inconsistent results.