Washington County reinstates quarantine to prevent emerald ash borer spread

PORTLAND, Ore. (KOIN) – The emerald ash borer quarantine that expired in May in Washington County has been reinstated to help prevent the spread of the invasive insect, the Oregon Department of Agriculture said. 

The quarantine, which had been in effect from Dec. 20, 2022 to May 16, 2023, prohibited people from moving tree materials from all ash, olive and white fringe trees to places outside Washington County. These are all tree varieties the emerald ash borer is known to target and kill. 

It included logs, green lumber, nursery stock, scion wood, bud wood, chips larger than 1 inch by 1 inch, mulch, stumps, roots, branches and firewood of hardwood species.  

As of June 16, the temporary quarantine has been reinstated. However, it now excludes materials from olive trees. 

The newly adopted temporary quarantine is set to expire on Nov. 11, 2023. 

ODA said it will continue to evaluate new data on the spread of the emerald ash borer to determine if a quarantine is still needed past that date. 

So far, the emerald ash borer has only been detected in Washington County and state officials are working to prevent it from spreading to other Oregon counties. 

The invasive pest was first discovered in Oregon in June 2022 when it was spotted on several ash trees in Forest Grove. This was the first confirmed sighting of the emerald ash borer on the West Coast. 

However, after the discovery of the emerald ash borer in June 2022, the ODA said it believes the insect has been in Washington County for at least 3-5 years. 

These invasive and destructive beetles have killed up to 99% of the ash trees in some North American locations. At least five ash species native to the Central U.S. have become critically endangered as the emerald ash borer spreads across the country. 

The emerald ash borer has also decimated ash trees in parts of North America outside the U.S., and in Europe. Its larvae burrow into the bark of ash trees, causing the canopy to die, which will ultimately result in impacted trees dying. 

Within a decade of the emerald ash borer’s arrival in an area, most ash trees will be dead or dying, the Oregon Department of Forestry said, putting the state’s native Oregon ash tree at risk. 

Researchers say olive trees and white fringe trees could also be impacted and are known to host the insect. That’s why materials from these trees were both included in the first quarantine and why fringe tree materials continue to be controlled in the newest quarantine. 

So far, the emerald ash borer has only been detected within the city limits of Forest Grove, ODA said. 

The emerald ash borer is about a half-inch long and an eighth of an inch wide. It’s known for its metallic, shiny green color. The insect is native to Asia. 

Signs of infestation include thinning and yellowing leaves on trees, bark splitting, D-shaped holes in tree bark, and basal shoots. 

There are steps the public can take to help control the spread of the emerald ash borer. 

The first is to report any and all sightings of the beetle. Anyone who sees an emerald ash borer should make a report of it online at the Oregon Invasive Species Council Hotline. 

Anyone looking to dispose of tree materials that are included in the quarantine can do so at approved disposal sites. A list is available online. 

The Oregon Department of Forestry also recommends towns remove ash trees from their list of approved street trees. 

Officials recommend planting resistant species in place of the ash trees — like Oregon white oak, incense cedar and Chinese pistache.