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Invasive Japanese beetles will be problem again this year

Friday, February 8, 2013 | 2:28 p.m. CST; updated 2:47 p.m. CST, Friday, February 8, 2013
Japanese beetles are expected to return this summer and cause damage to agricultural and garden plants. The species population increases with rainfall.

COLUMBIA — When Ben Puttler began tracking Japanese beetles in 1996, none of the invasive species turned up in his trap at the A.L. Gustin Golf Course.

“It wasn’t until 2002 when I found 15 that I knew the population was established in Columbia,” he said.

Japanese beetles

  • First found in U.S. in 1916, possibly coming in iris shipments from Japan.
  • Found in Missouri by 1934, mostly living in golf courses and plant nurseries. It is believed the beetles arrived in the soil of some kind of nursery stock or the adults traveled slowly from the eastern U.S. (they can travel an average of three miles per year).
  • Adults are about a half-inch long with metallic green coloring and wing covers of either bronze or copper.
  • Japanese beetles eat more than 400 different kinds of vegetation—linden trees and roses are among their favorites, along with soybean and corn crops.
  • More information about Japanese beetles, including different ways to control them, can be found at the Missouri Botanical Garden website.

Sources: Wayne Bailey, entomologist for MU Extension; Missouri Botanical Garden


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The MU assistant professor emeritus of plant sciences found approximately 23,000 beetles in his trap in 2012 during the season, which ran from the last week in May to the end of August.

In the St. Louis and Columbia areas, the beetles left linden trees almost completely defoliated, said Wayne Bailey, an entomologist for MU Extension.

The beetles, which eat upwards of 400 different kinds of plants, also count roses among their favorites — not to mention agricultural and garden crops.

The number of beetles Puttler found has slightly decreased over the past two years, suggesting the population might be peaking. Even so, people can expect to see continued damage to plants and trees this summer, he said.

The severity of this year's outbreak will hinge on factors such as ground moisture in the months leading up to summer, Puttler said.

“In general, dry winters and dry springs can hamper the population,” Puttler said.

“The grubs feed close to the surface on the roots of plants, so dry soil slows them down,” Bailey said.

Even though the grubs have a higher survival rate in warmer winters, they are somewhat protected from the lower temperatures because they live in the soil, he said.

Despite Missouri having a drier winter in 2011-12, there was still significant damage to plants in the eastern half of the state last year, Bailey said, and probably the worst damage Columbia had seen from the beetles.

“The eastern half had quite a bit of damage last year and we’re seeing more and more damage in the western half with normal rainfall,” Bailey said. “It is probably going to be worse this summer in the western half than even here.”

Last year, farmers probably had fewer problems with the beetles than normal, but if this year has more normal rainfall, they can expect a lot of damage, Bailey said.

“The population will probably increase with the rain we’re getting,” Bailey said. “The rains coming through now will help them survive.”

Puttler's forecast: "It’s going to be a pest. Period. Let’s put it that way.”

With invasive species such as the Japanese beetle, populations tend to increase as they colonize for seven to 10 years before slowly leveling out, Bailey said.

“When we get invasive species introduced to us, they colonize and have a peak population for awhile because the controls don’t come with them,” he said.

Betsy Kohler, a home gardener and owner of Muddy Boots, a gardening business southwest of Columbia, said the beetles were a particular problem last year for her Japanese maples and roses.

“They can really do some damage to the leaves,” she said. “During their active time, it’s like ‘wow.’ It’s pretty scary if you’re not a bug person.”

Most of the damage done to ornamental plants and gardens is from the adults. The damage to crops such as soybeans and corn is from both adults and grubs, the larval form of the beetles that overwinter in the ground.

Mervin Wallace of Missouri Wildflowers Nursery, south of Jefferson City in Brazito, has taken preventative measures to protect the native grasses he sells.

“We have to treat the soil that we grow our grasses in to kill the grubs,” he said.

Wallace also used some traps last year for the adult beetles. He said the traps were so effective at attracting beetles, he wasn’t sure whether they helped or hurt.

“It was a little windy that day, so we had them swarming around us before we even had the traps assembled,” he said.

To avoid having the beetles swarm to your plants, it is important to place the traps away from the areas you want kept safe.

“We tell people to not put traps by the plants you’re trying to protect because of the pheromone. The beetles will be attracted right to it, so you should put them on the perimeter of the area around your plants,” Bailey said.

Researchers have discovered a wasp, Tiphia vernalis, in Meramec State Park in Sullivan that is believed to be beneficial for reducing the Japanese beetle population, Puttler said.

“There is a possibility of obtaining this wasp, but they are $10 each with a minimum purchase of 100,” he said. “We have the means to get these, but the possibility is really pretty slim.”

Natural controls on the beetle are better established in the eastern U.S. but are less common in mid-Missouri, Bailey said.

Other beneficial biological organisms can be found locally, such as various bacteria and fungi that naturally occur in the soil, but they do not do enough to help, Puttler said.

“There are natural enemies," he said. "It’s just that nobody’s really working on them to a great extent."

Supervising editor is  John Schneller.


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