FOREST GROVE, Ore. — The Oregon Department of Agriculture has reinstated a temporary quarantine in Washington County to prevent the spread of emerald ash borer, an invasive insect that has killed hundreds of millions of North American ash trees nationwide.

Emerald ash borer was found last year in planted ash trees at a middle school parking lot in Forest Grove, about 20 miles west of Portland. 

A quarantine was first adopted in June 2022, restricting the movement of olive, ash and fringe white tree material outside the county that could harbor the small but destructive beetle. 

The newly imposed quarantine excludes olive trees, but still applies to ash and fringe white tree material — including logs, stumps, green lumber, nursery stock, scion wood, roots, branches, chips, mulch and firewood. 

Native to Asia, the emerald ash borer arrived in the U.S. in 2002. Researchers consider it North America’s most damaging forest pest. 

About the size of a cooked grain of rice, the shiny, metallic green insect has since spread to 30 states and Canada. Its discovery in Oregon marked the first sighting on the West Coast.

Signs and symptoms of emerald ash borer in infected trees include:

• Crown dieback in heavily infested trees.

• D-shaped emergence holes in bark, about 3 millimeters in size.

• Sucker shoots emerging from trunk.

• S-shaped galleries underneath the bark.

• Trees dying from the top down.

ODA also recommends several treatments for potentially infected tree material, including:

• Debarking and removing at least 1 inch of underlying wood.

• Grinding or chipping material to 1 inch or less in size.

• Heating wood to a minimum of 140 degrees for at least 60 minutes.

• Burying material under at least 12 inches of topsoil.

• Incinerating wood.

• Secondary processing into byproducts, such as paper, fiber board or pellets. 

The temporary quarantine will remain in effect until Nov. 23, and could be amended or extended as more data becomes available. 

Invasive emerald ash borer found in Oregon — first sighting on West Coast