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Invasive Japanese beetles spotted in Cedar Mill area

Insects feed on popular Oregon plants; likely arrived via infested plant material.

PHOTO COURTESY OF THE MINNESOTA DEPARTMENT OF AGRICULTURE - Japanese beetles have been wreaking havoc on plants elsewhere in the United States for decades, but a localized infestation in Cedar Mill has taken the Oregon Department of Agriculture by surprise.An eye-catching, iridescent species of insect has popped up in Cedar Mill for the first time, according to the Oregon Department of Agriculture — and it means nothing good for local gardeners, growers and farmers.

The Japanese beetle is an invasive species that has not generally spread west of the Rocky Mountains in North America, according to Clint Burfitt, who manages the insect pest prevention and management program for the Department of Agriculture. But the voracious insect was detected north of Highway 26 west of Portland this year, likely having surfaced due to soil or plant material infested with its eggs or larvae being brought to the area, Burfitt said.

“This thing is not going to naturally migrate to a place like western Oregon,” Burfitt said, adding, “It's only going to get here artificially, through the help of humans.”

The Department of Agriculture announced that 265 Japanese beetles, a “record number,” had been found in traps in Washington County as of Aug. 29.

According to its report, “It appears the infestation has been present for at least more than a year but not detected until this summer.”

As Burfitt described it, the preferred menu of the adult Japanese beetle lines up uncannily well with many of western Oregon's most popular and iconic plantings.

“Japanese beetles like to eat a lot of the same types of plants that we love to grow,” Burfitt said. “Some of the top ones would be roses, hops, grapes. We've recently had a publication that indicated that it enjoys cannabis, also.”

The female beetles lay their eggs in turf. The larvae then surface, and once they grow into adults, they will eat leaves and fruit, Burfitt said.

“The main problems with Japanese beetle is that the adult population can become very abundant,” he said.

Burfitt explained further, “If you were to just let this thing go, it would become an economic pest for many of the agricultural industries in the state of Oregon, and then it would become a significant nuisance pest for … the residents of western Oregon.”

“I can say, if these beetle are established, it will become a large issue for a number of crops Oregon agriculture exports out of the state or country such as nursery crops and blueberries,” said Robin Rosetta, an Oregon State University entomologist who works at the North Willamette Research and Extension Center in Aurora. “These beetles can directly damage a wide range of plants including our iconic roses. The larvae of the beetles are very destructive to turf. Likely much more pesticide usage would occur if they become established.”

The good news, according to Burfitt, is that with fall right around the corner, gardens, nurseries and farms in the area are basically safe for now. The bad news is that the beetles could be back, and in greater numbers, in the spring.

“The damage is done for the year,” he said. “The adult females have laid their eggs in the turf grass. … Adult beetles will become even harder to find here over the next few weeks as things cool off.”

The Department of Agriculture will be considering how to respond to the infestation in Cedar Mill, Burfitt said.

“This is pretty surprising,” he said. “This is the most beetles we've ever detected in Oregon. But the good news is it's very localized.”

The areas where beetles were caught in early detection traps are in the vicinity of Northwest Saltzman and Thompson roads, according to Burfitt. He said there appear to be two areas of concentration about a half-mile apart, with some smaller pockets in between them.

Because it is a recent infestation, Burfitt said, the beetle population has not exploded out of control yet, as it has in many parts of the United States east of the Rockies.

“Most people aren't going to be able to notice damage or adult beetles associated with the outbreak right here,” he said.

However, Burfitt added, if anyone does see what they suspect to be a Japanese beetle — although it does have some lookalikes, as noted by the Minnesota Department of Agriculture — they should contact the Oregon Invasive Species Hotline online or by calling 1-866-468-2337 (1-866-INVADER).

By Mark Miller
Assistant Editor
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