Don't trap the Japanese beetles wreaking havoc on your garden — that'll make it worse

They have spent the last century traveling westward from the East Coast, and now millions of Japanese beetles have made their home feasting on rose bushes and gardens in Kansas City.

"Japanese beetles have this nice buffet of plants to feed on," said Kansas State University entomology professor Raymond Cloyd.

The creepy crawlers started appearing in the metro area about 20 years ago and have been slowly increasing in numbers until a peak last summer, said Dennis Patton, a horticulturist for the Johnson County K-State Research and Extension Office in Olathe.

"Last year was kind of the 'all hell broke loose year' where they have been everywhere," Patton said.

The bugs, which are active for four to six weeks during June and July, returned this year with similar numbers, Patton said.

Matt Stueck, vice president of Suburban Lawn and Garden, said he expects his stores to see a 20 to 25 percent increase in sales of Japanese beetle-related products. He joked that he wasn't sure the stores would have customers if it weren't for Japanese beetles.

"We have not exceeded last year's sales but we're already pretty close, and we have weeks to go," Stueck said.

Kansas City has likely hit the halfway point for Japanese beetles this year, Patton said. Though they may be a nuisance, that's all they are. The bugs don't cause any lasting harm to the plants they feed on. Japanese beetles eat the leaves and petals of sweet smelling plants like roses and linden trees — but they don't kill them.

"They’re ruining the aesthetics of the plants," Cloyd said.

For plants like roses, however, the aesthetics are important. To minimize damage from the pests there are a few tactics available to gardeners.

One common practice is to trap the insects, but Patton and others advised against it.

Beetle traps attract the bugs with a sweet scent, but they pull more bugs into a yard than would have been there beforehand. Oftentimes those beetles feed on plants before finding their way into the trap. Traps are only effective if they are arranged every few feet around the perimeter of a yard, Patton said.

Two effective options, according to Cloyd and Patton, are to spray plants with chemicals to kill the bugs or to knock the bugs off of plants with your hand into a bucket of soapy water.

Each has its drawbacks. Knocking the bugs down is organic but can be time intensive and must be done every day. Anne Wildeboor, a horticulturist at the Overland Park Arboretum, said volunteers spend a couple of hours every morning knocking down beetles.

"With the public being in the gardens we try to be as organic as we possibly can," Wildeboor said.

Using chemicals can harm beneficial insect populations.

"The insecticides that are effective are very harmful to bees," Cloyd said. "People need to really be cognizant and apply them when bees are not present."

Specifically, Cloyd said chemicals should be applied early in the morning or late in the evening to avoid harming other insects.

In the next few weeks, however, the Japanese beetle will finish out this life cycle. The larvae will live within grassy plants through the winter and they will return to gardens next summer.

Although Patton said the population will fluctuate, Kansas City residents can expect to put up with the Japanese beetle for "eternity."

This story was originally published July 3, 2018 at 4:52 PM.