Alfresco dining? How to handle Japanese beetles, other pests chewing up garden greenery

Has some creature been chomping the leaves of your beloved rose bushes?

Don't get antsy. It's probably only a Japanese beetle having lunch, says plant health expert Paul Hacholski, who works for the Lurvey Garden Center & Landscape Supply in Des Plaines.

The insects emerge in late June or early July and remain for about six weeks. During that time, they chow through fruit, vegetable and flowering plants, linden, birch, hollyhocks and elms, among others.

"They don't necessarily kill a plant," Hacholski said. "They skeletonize the leaves, meaning they eat everything between the veins. It's like they don't like the crust on the toast."

Plants whose leaves have sporadic holes were probably feasted upon by slugs or earwigs, Hacholski said. "Everyone's having lunch."

And the menu is vast and varied, according to Ken Johnson, horticulture educator with the University of Illinois Extension.

"Japanese beetles feed on over 300 plants," he said.

In addition to roses, Johnson says, the beetles favor fruit trees, hibiscus, sweet corn, green beans and raspberries among others. They tend to avoid red and silver maples, evergreens, pine trees, spruce and arbor vitae, he said.

Unlike the emerald ash borer, which kills trees, or defoliators, "Japanese beetles aren't causing that much damage," Johnson said.

And they rarely kill a plant unless it's already compromised, Hacholski said.

"Leaves come and go," he said. "If the roots are alive, they'll come back."

Thomas Fritz, plant health care specialist with the Chicago Botanic Garden in Glencoe, agrees. He says unless a plant is under stress from other conditions, such as drought, or on the verge of dying, 95% of plants survive the onslaught.

A warm winter means more insects, while a colder, harsher winter typically translates to fewer insects, says Fritz, who estimates Japanese beetles will reach their peak next month.

"They can be quite a nuisance when they arrive," said Fritz, who recommends gardeners adopt a preemptive approach.

He says a strong stream of water from a garden hose will flick insects away.

"If you're not squeamish, you can pick them off the plant and drop them in soapy water. That will kill them," he said. "It's safe and effective, but you have to be vigilant."

Johnson advises picking insects off plants during the evening, ideally over the first few weeks of their emergence. He says covering high-value plants such as roses with netting, secured tightly around the base, will also keep beetles at bay.

Using grub killers on the lawn in May and June before the pests emerge is a preemptive way to eliminate them, Hacholski said.

Japanese beetle traps, which lure bugs away from savory vegetation, are another option, Fritz said, but they work best in large yards. In smaller yards, the traps can do more harm than good because they can invite greater quantities of bugs into the yard.

Another organic preventive is neem oil, which can be sprayed on the plant, making it distasteful to Japanese beetles.

"It will deter them from feeding on the plant," Fritz said.