Emerald ash borer (EAB) is considered the most destructive forest pest in North America and can kill all species of ash trees. In the greater Portland area and throughout the Willamette Valley, native Oregon ash (Fraxinus latifolia) is of particular concern in our region. This tree is critically important for forested wetlands and riparian areasRiparian areas The land alongside a creek, river, pond, or other body of water. For some ash-dominated wetlands, there is no native canopy-forming tree that grows in the same conditions.
Adult beetles lay their eggs inside ash trees. The larvae feed on the tissue below the bark, slowly killing the tree. Larvae pupate into adult beetles inside the tree and bore their way out through the bark. Adults then feed on the leaves of host trees.
Most females lay their eggs on trees within 100 yards of where they emerged but can disperse up to 2 to 3 miles. Therefore, ash trees within 30 miles of an infestation are considered at risk. It can take 4 to 6 years for an infested tree to die, and there may be no noticeable effects for the first few years.
The insect is native to northeast Asia and was unintentionally introduced to the U.S. likely in ash wood used in cargo shipping. It was first detected in Michigan in 2002 and has since spread to 36 states and 5 Canadian provinces. It was discovered in Oregon in 2022. EAB has spread from people moving firewood, logs, or ash trees from nurseries, as well as by the natural movement of the insect.
What you can do
Prevent new introductions: If you use firewood, buy and use firewood locally (within 10 miles of harvest location) and transport only firewood that has been heat-treated and certified as pest-free. Transport of firewood and nursery stock are the major pathways for the spread of this destructive beetle.
Slow the spread:
Look for the following signs of poor tree health and symptoms of emerald ash borer infestation:
- Dead or dying ash trees or branches, particularly high up in the canopy, where the adult beetles typically start their feeding and laying of eggs. Tree die-back can be subtle at first, so it’s important to look closely.
- Epicormic branching — branches that grow out of the trunk or straight up out of the base of larger branches. This is the tree’s last gasp at life.
- Splits along the bark and S-shaped tunnels under the bark
- Patches of lighter wood where woodpecker have pecked to get to insects. Use binoculars to look high in the canopy. Also look lower down on the trunk.
- Very small D-shaped holes in the bark of the tree. Adult beetle exit holes are 3 mm in diameter — less than the size of a pencil eraser. These are hard to see!
Learn to identify the beetle:
- Small and slender, metallic green adult beetles grow up to 0.3 to 0.5 inches (13mm) in length and 0.07” in width. Adults are active from late May to early July. Adult beetles are typically found after trees are already heavily infested and damaged.
- See what EAB looks like compared to similar looking insects.
Report any suspected emerald ash borer insects or signs of infestation to: www.oregoninvasiveshotline.org or call 1-866-INVADER
What we are doing
We are partnering with state and federal invasive insect pest managers to detect signs of EAB in our district and SLOW its spread in Oregon. Specifically, we are:
- Monitoring ash trees on project sites where we know we have native Oregon ash.
- Setting out traps where we know ash trees are growing. We began this step in 2021 to help find any newly arrived beetles in natural areas and urban settings. We are working closely with our federal partner on this effort, U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS).
- Assisting partners, such as Oregon Department of Forestry and the U.S. Forest Service, to map Oregon ash statewide.
- Utilizing Oregon Department of Agriculture survey tools to map healthy and stressed ash trees.
- Continuously training ourselves about the best response to the arrival of EAB in our area.
- Considering the use of “trap trees.” A trap tree is an uninfested ash tree that is deliberately girdled / slowly killed to attract emerald ash borer to it and spare nearby trees. EAB are especially attracted to stressed ash trees. The trap tree is later cut down if infested and the pest larvae die.
- Learning more about the use of insecticides to kill Emerald ash borer in select trees, as well as the use of parasitoids–native predators of EAB in its home range in Asia–which has proved at least partially successful on the East Coast.
- Advising land managers with ash trees. Please let us know if you have questions or want to help!
- OSU Extension Fact Sheet
- Take the free and fun Oregon Forest Pest Detectors Online Course to be a better detector.
- USDA Emerald ash borer info brochure
- Oregon Department of Agriculture info page
- USDA Animal and Plant Health Inspection Service (APHIS) info page
- Oregon Department of Forestry: Roundup of Oregon EAB news
- Oregon Department of Forestry: Readiness and Response Plan for Oregon
- City of Portland
- Xerces Society
- See the regions in Oregon most at risk.