Japanese beetles make return appearance

Japanese beetles can feast on a plant’s leaves until they resemble lace, experts say.

Japanese beetles can feast on a plant’s leaves until they resemble lace, experts say. Submitted photo

The iridescent pestilence has returned for the summer — in droves.

With a trap that hosts around 1,000 new Japanese beetles per day, horticulture specialist James Quinn believes the infestation of Japanese beetles is far from its conclusion.

“If you’re wondering if they’re back, they’re back,” he said.

Though Japanese beetles can and do envelope the leaves of a knock-out rose like a lustrous black armor this year, their numbers have halved since 2012, according to Quinn.

In 2012, he captured approximately 2,000 beetles per week during the climax of the invasion. Quinn has been trapping beetles near the University of Missouri Extension Office on Tanner Bridge Road since 2007.

“Each year, there were more. We thought they can’t get worse, but they did. They were horrendously worse,” Quinn said of the 2012 beetle population.

Over the course of the summer, the beetles’ population level in the Jefferson City area resembles a bell curve. Around July 3, Quinn trapped approximately 300 beetles per day, and the numbers have only escalated and remain constant at triple the original level.

Japanese beetles concern garden owners and agriculturists because of their ability to damage leaves and defoliate plants.

In addition to roses, the beetles also feast on blackberries, raspberries, grapes and some other perennials.

Though Japanese beetles can devour leaves until they resemble lace, garden owners should “consider tolerating them,” Quinn said. “They typically aren’t going to kill a plant. It’s more a cosmetic, unsightly thing,” he said.

Quinn hopes the Japanese beetle population will one day diminish dramatically, and he cited Japanese beetle population reductions in Springfield as evidence for that possibility.

“They used to be terrible in Springfield, but they’re not any more. We’re waiting for that to happen in Jefferson City. We’re anxious for that year to happen,” he said.

Gardeners and commercial growers face an obstacle in eliminating — or even reducing — the presence of the pests on garden plants.

Though the pesticide Sevin can eradicate the insects, it also can harm bees, which is why Quinn recommends tolerating the beetles.

Instead, Quinn encouraged gardeners to seek other pesticides like Bayer Advanced Tree & Shrub for pest control.

Additionally, traps that are advertised to catch Japanese beetles may, in fact, attract more beetles to the vicinity of plants that a gardener may be attempting to protect, rendering the trap disadvantageous.

Because Japanese beetles begin as grubs underground, a gardener can apply milky spore to reduce the grub population and, thus, the beetle population.

Though this solution can prove quite effective, Quinn said, most gardeners do not consider it because the grubs are not often visible above ground.

“Ninety percent of people don’t care about the grubs. It’s out of sight, out of mind,” he said.

Though many gardeners do not use milky spore, Anika Rudloff attributes her nearly complete lack of Japanese beetles to milky spore, she said.

For gardeners who invest substantially into roses and other plants, the $80 investment into milky spore may prove worthwhile, Rudloff said.

As a Master Gardener, Rudloff would often spend up to 90 minutes per day handpicking the beetles off her other plants, including her porcelain vine, calla lilies, hibiscus and blue plumbago.

“Most insects don’t cause that much damage (as the Japanese beetles). It’s not fun to pick them off,” she said.

Though Japanese beetles may not cause consequential monetary damage for home gardeners, they could inflict devastation on farmers’ crops, including corn and soybeans, according to regional agronomy specialist Joni Harper.

Japanese beetles frequently attack crops during their more vulnerable growth stages including the silking stage of corn and the flowering stage of soybeans.

Because the beetles have the capability of causing economic damage, Harper believes it is “important to scout fields,” she said.

Farmers should consider an “economic threshold” when deciding whether to spray fields to eliminate Japanese beetles.

Harper considers 25 to 30 beetles on each plants to be “high infestation” that warrants spraying.

Additionally, a drought or other unfavorable natural condition can increase the stress on a plant, she said, adding that “any stress on plants will cause more damage.”

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