Hordes of Japanese beetles are invading Iowa vineyards (and your yard may be next)

Julianna and Andy Hrasky got a nasty surprise when they returned home last month: Thousands of Japanese beetles were eating their way through the couple's western Iowa vineyard.

"One day was fine, and the next, they had taken over," said Julianna Hrasky, whose family left their vineyard — Prairie Crossing Vineyard and Winery near Council Bluffs — for a couple days.

"We weren’t expecting them to come that fast and furious," she said. "The quantity was extreme."

The pests are invading the state in numbers few Iowans have experienced before.

"This is the highest populations I've ever seen," said Mike White, an Iowa State University Extension viticulture specialist. "Boy, there's lots of them."

Grapes and other fruit trees and vines are among the pests' favorite feasts, but they're also eating foliage from trees, shrubs and flowers and wreaking havoc with home gardens and flower beds.

About 50% to 60% of Iowa vineyards are spraying pesticides for Japanese beetles, White said.

"We're doing everything we can now to control them," said Julianna Hrasky, adding that the insects mostly wiped out one grape variety, but they hit other vineyards less hard.

The trouble doesn't end with the adults, which die after five or six weeks.

Once the beetles mate, they lay their eggs underground, where the hatching grub larva feed on the turfgrass roots, potentially causing the grass to wilt and fade this fall.

It's unusual for one insect to cause so much damage, said Donald Lewis, Iowa State University entomology professor.

"It's a double whammy," he said.

As difficult as it might be, though, Iowans may decide against fighting back, Lewis said.

Protecting trees, shrubs and flowers requires several pesticide applications, a move some homeowners may be uncomfortable with.

"As unappealing as it is, the practical response for many is to look the other direction," Lewis said. "Tolerate the damage, understanding that defoliated trees are not dead.

"The tree is still alive. It just won't be pretty for the rest of the summer. You might have lost flowers … but the plants are likely to survive."

The Japanese beetles' invasion isn't new.

Gardeners first discovered the Japanese beetle in U.S. in 1916, but the insects didn't arrive in Iowa until 1994.

The pests have been marching their way through Iowa ever since, wreaking havoc in nearly 70 counties.

One reason this year feels intense is that the Japanese beetle experienced colony collapse in Iowa's harsh 2013-14 winter. But they've rebounded with gusto, Lewis said.

"Insect populations go through explosion and crashes," he said. "It's a way of life."

The Hraskys estimate the pests caused their winery about $20,000 in losses from the one variety of grapes. The couple must drop the fruit, with three-fourths of the foliage eaten away.

The leaves provide the fruit the nutrients it needs. Without the foliage, the vine would struggle to fill the fruit, stressing it and making it difficult to survive through the winter.

"We have our fingers crossed they won't cause any more damage," Julianna Hrasky said.

White said grapes, Linden trees and roses top the Japanese beetles' favorite foods list.

"When they get together, they emit a pheromone or a scent … that attracts more in," he said. "It says, 'lunch is over here.' And they'll fly 3 miles to get to that scent."

That's why problems develop fast, White said.

"We went from one to two beetles to a million overnight," said Suzie Berregaard, who owns In Vino Veritas Vineyard and Winery near Grimes with her husband, John Nuhn.

Japanese beetles are among a long list of threats grape growers face, including hail, disease, birds and other insects, Berregaard said. 

"There are so many ways, so many predators and pests that can get in the way of you getting a crop," she said, adding that she didn't think the beetle damage her business saw would impact fruit production.

White and Lewis recommend that homeowners not use beetle traps.

"It may be emotionally satisfying to see … thousands of dead beetles," Lewis said, "but there are still a million more out there.

"Trapping does not alter the overall population. And yes, traps attract more than they catch, so if you disregard our advice and put out a trap, put it as far from your crop as possible."

Or, as White joked: "Put it in your neighbor's yard."

What about my yard?

ISU’s Donald Lewis said a high number of Japanese beetles on your flowers and trees in the summer “do not predict” a large number of grubs in the fall that could damage your lawns.

"To say your lawn will be ruined by white grubs — Japanese beetle and masked chafer larvae — without insecticide treatment is fraud intended to sell more pesticide," Lewis wrote to county extension offices this month.

For more information, go to hortnews.extension.iastate.edu/white-grub-control-turfgrass.