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ON THE WATCH FOR JAPANESE BEETLES

GARDEN TIPS – Written by Marianne Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Published September 4, 2016

It was never a matter of “if” the Japanese beetle would reach the Pacific Northwest, it was a matter of “when” it would get here. That could be now. Numerous adult beetles have been trapped and found eating on roses and other plants in Portland, according to the Oregon Department of Agriculture (ODA). ODA says that this suggests “a breeding population of the non-native insect has been established.”

Uh oh! This is terrible news for gardeners and growers. A University of Kentucky publication says that “the Japanese beetle is probably the most devastating pest of urban landscape plants in the eastern United States.”

I am willing to bet that if you migrated to this area from the eastern part of the US, you already know too well why a Japanese beetle infestation is scary. As a pest, this rather pretty beetle packs a double whammy. Its grubs feed on grass roots and can be very damaging to lawns. The extremely voracious adults are omnivorous, feeding on a wide variety of plant hosts including roses, ornamentals, trees, shrubs, fruit, and vegetables, often devouring the upper sides of plant foliage, leaving only the skeleton of veins and midribs behind.

The Japanese beetle is one of the scarab beetles and could be considered attractive if you like beetles. The adult beetle is almost ½ inch in length with metallic copper wing covers and clubbed antennae. The head and thorax in front of the abdomen are metallic green. Along the sides of the abdomen are hairy patches that look like white spots.

Like so many damaging insect pests, the Japanese beetle is an alien, coming here from Japan. It was first identified in the eastern US in 1916 and it became established in all the states east of the Mississippi, except for Florida, by 1998.

Besides its rapacious appetite, this beetle’s propensity for aggregating on plants can lead to rapid and complete defoliation of a plant. Japanese beetle-damaged plants emit volatile chemicals that bring more beetles to the party. In addition, the unmated females emit a pheromone to attract even more hungry beetles. Once done with one plant, they move onto another.

Thankfully, there is only one generation of Japanese beetles a year, but with each adult female laying from 40 to 60 eggs, populations can build quickly. Control with pesticide applications is aimed at both the adults on plants and their grubs in the soil. You may see Japanese beetle traps advertised for their control, but university research indicates that the traps are effective in monitoring for the beetle’s presence, but not for control. In fact, the traps can result in more of the beetles finding your yard and causing damage.

Over the years ODA has been working to contain and eradicate any Japanese beetle infestations that they have detected. They believe that the origin of these infestations are air cargo carriers coming in through the Portland International Airport. ODA estimates that the current infestation has been present for more than a year without detection. Right now they are trying to pinpoint where the breeding population is located so they can treat the infestation next year.

For us in Washington, it is good to know that the Washington State Department of Agriculture (WSDA) has been on the watch for the Japanese beetle and has been conducting trapping each year since the mid-1980s to make sure they have not become established anywhere in the state. So far, WSDA has not had to conduct eradication measures on a breeding population yet. I hope it stays that way.

Garden Tips, WSU Extension, Benton County, 5600-E West Canal Drive, Kennewick, WA 99336-1387, 509-735-3551, Contact Us

WSU Extension, Franklin County, 1016 North 4th Ave, Pasco, WA 99301-3706, 509-545-3511, Contact Us
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