Japanese beetle recorded in 69 Iowa counties this season

The insects can defoliate up to 300 plant species

Source: ISU Extension & Outreach. Map by John McGlothlen / The Gazette

Japanese beetles have been reported in 69 Iowa counties. Courtesy of ISU Extension & Outreach.
Japanese beetles have been reported in 69 Iowa counties. Courtesy of ISU Extension & Outreach.

Japanese beetles have been an issue for Fireside Winery in Marengo for the past couple years, but not as much of a nuisance as they have been this season.

“There’s been way more,” said Zach Bott, winemaker at Fireside. “They just showed up and swarmed — 20, 30 to 40 (Japanese beetles) per plant.”

With 14 acres of wine grapes — including Marquette, Frontenac, California Carbernet, Brianna — to cover, Bott said the Fireside crew has sprayed insecticide on the leaves three times already and are prepping for a fourth — double from years previous.

The spray does not affect the wine as it is all removed by the time of harvest, he said.

“We’ve been able to stay on top of it,” Bott added. “We can’t lose our grapes.”

Donald Lewis, an entomologist with Iowa State University, confirmed this was a recent record year for Japanese beetles, with an outbreak of the insect reported in 69 of Iowa’s 99 counties.

Japanese beetles, noted for their hard wingcases, emerge annually in mid-June and live for roughly six weeks into early August. But Lewis said this year’s population started the third of week of June — and they all came at once.

Lewis said the beetles reached their peak during the first week of July and have been dying slowing since. He believes they arrived in such large quantities because of the hot, dry winds during June.

The beetles usually are isolated to random areas. For example, they may be found in one city but not the other, or even in one backyard and not the one next to it.

“It’s not that they move in a steady wave across the county,” Lewis said. “They leapfrog and hopscotch.”

While not as devastating as the Emerald ash borer, which has been detected in 51 Iowa counties, the Japanese beetle causes a different kind of havoc.

“They can be quite destructive,” Lewis said. “They can ruin the beauty and the income from a large number of plants” — up to 300.

The cause for the outbreak this season, Lewis said, can be traced to a dozen factors, from the time the Japanese beetle eggs are laid in August, all the way until they emerge in June. These factors could include changes in weather, the eggs’ environment and whether or not it is getting food.

“Because each one of those pieces worked to the benefit of the beetles, we had an outbreak this year,” he said.

The good news, however, is that an outbreak this year does not equate to an outbreak next year.

“They’re definitely a nasty bug,” Bott said. “They don’t smell good and they don’t look good. They’re kind of a pain. We’re looking forward to not having to deal with them this year” beyond August.

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