A Japanese beetle.

More than 20,000 Japanese beetles have been trapped in and near a Central Washington town, an infestation the Washington Department of Agriculture hopes to contain with a quarantine.

The department has filed a notice that it intends to establish a quarantine in portions of Yakima and Benton counties. Grandview, the outbreak’s epicenter, is in Yakima County and just west of Benton County.

The department has not determined the boundaries or what would be regulated under a quarantine, spokeswoman Karla Salp said Monday. Before establishing a quarantine, the department would analyze how it would affect businesses, she said.

Japanese beetles eat fruit, flowers and buds, and damage roots. The invasive pests are widespread east of the Mississippi. If established in Washington, the beetles would be a threat to agriculture, according to the department.

The Oregon Department of Agriculture has been battling Japanese beetles in the Portland area since 2016. In Washington, beetles are being trapped by the thousands close to farms and nurseries.

The beetles have the potential to affect export markets for farm goods grown in the area, according to the department.

To eradicate beetles, Oregon spreads a granular larvicide in the spring on lawns and planting beds. The state agriculture department last spring treated 12,000 properties over 4,000 acres with Acelepryn G.

Landowners who didn’t consent to the treatments were served warrants allowing the department onto their property.

The beetles spend about 10 months underground. The trapping season is coming to a close, Salp said. The department likely will use chemicals against the beetles in the spring.

The department has not yet presented a formal quarantine proposal or opened a comment period.

Anyone who would like to participate in formulating the rule can contact Assistant Director Brad White of the Plant Protection Division at (360) 902-1907 or bwhite@agr.wa.gov.