For twenty years, a pretty little insect has been traveling across the nation and it has finally arrived in Oregon, as specialists knew it eventually would. Its arrival is no means for celebration, as this non-native beetle is infamous for wreaking havoc on ash trees and our native Oregon ash tree will be no exception.
The emerald ash borer (EAB) is aptly named. This invasive insect is a shiny emerald green and it bores into ash trees where it fulfills its destructive lifecycle, killing its host in the process. In its native habitat of northeastern Asia, EAB is more of a nuisance than an existential threat to ash trees. The trees there have natural defenses and EAB populations are suppressed by predators. Sadly, in North America, host trees lack these defenses and there aren’t strong local predators, so EAB populations have ballooned, and ash trees have paid the price. Tens of millions of ash trees have been killed by EAB since it was first spotted in Michigan in 2002.
How did the emerald ash borer get here?
Like many invasive species, EAB was most likely transported to America unintentionally, likely by hitching a ride on a cargo ship. Once in North America, it probably spread by infesting a tree that was chopped into firewood and driven miles away or by occupying nursery trees that were then distributed across the region.
This is the case for lots of invasive plants and pests. That’s why it’s important individuals take care not to accidently spread an invasive species when enjoying the great outdoors. Read about ways you can reduce the spread of invasive species.
What are conservation agencies doing about EAB?
There have been about twenty attempts to eradicate the emerald ash borer in the United States, but none have been successful. Luckily, researchers and government agencies in states with EAB have learned important lessons about how to slow the spread and damage caused by the insect. This has helped communities recover and adapt to its presence. The Oregon Department of Agriculture (ODA) will lead the response team using the EAB Readiness and Response Plan for Oregon.
Because conservation agencies expected the arrival of EAB, seed collection programs have been underway for several years. The purpose of collecting seeds is to preserve and study the genetic diversity of Oregon ash trees. Eventually, these seeds can be used to start a selective breeding program that develops ash varieties that are more resistant to EAB. Although emerald ash borers will likely kill or damage most ash in its path, the hope is that one day stronger ash trees can be planted to replace the trees that are lost.
What can individuals do about EAB?
To help slow the spread of the emerald ash borer, individuals should learn how to identify an infestation and report it to the Oregon Invasive Species Hotline. Below is an overview of what to look for. For in-depth information on how to identify an infestation, refer to the Oregon Forest Pest Detector Field Guide.
How to recognize an ash tree (Fraxinus species):
- Ash are deciduousDeciduous Trees or shrubs that lose their leaves seasonally. trees, most are medium to tall.
- Our native Oregon ash (Fraxinus latifolia) grows in low-lying wet places. Although, ash trees of different types can also be found in backyards, along sidewalks, and in medians.
- It has compoundCompound A leaf consisting of several distinct leaflets joined to a single stem. leaves which are made up of 5 – 11 leaflets. Leaves form on opposite sides of a branch.
- Seeds are winged and hang in clusters.
- Mature bark has a diamond pattern.
How to identify an emerald ash borer (Agrilus planipennis):
- This insect has a slender, shiny green body that is about half an inch long. It’s about the size of a dime.
- When its wings are open, they reveal a red metallic abdomen.
- Its head is slightly indented with bulging eyes.
- They only fly for a few weeks per year – from late May through early July – when they emerge to mate and lay eggs. Because of its small size and narrow flight window, you are not likely to see an adult beetle. Although you may see them if there are many flying around a heavily infested tree.
- There are many similar looking bugs, become familiar with its look-alikes here.
Clues that point to an EAB infestation:
- Adult emerald ash borers are most likely to be spotted in June and July. Finding EAB is a good indication there is an infected ash tree nearby. EABs only feed on ash trees.
- Infested trees will drop leaves starting at the top of the canopy. Eventually the entire crown may appear thin or dead (no leaves).
- The tree may have branches popping out of the trunk below where the crown begins. This is a common sign that the tree is stressed.
- EAB larva create S-shaped galleriesGalleries Channels or engravings underneath a tree's bark created by insects. as they feed on the tree. When the infestation is far along, the S-shaped wiggles will be so numerous it can look like a plate of spaghetti.
- On heavily infested trees, the bark will sometimes crack, revealing the galleries underneath.
- Eventually, EAB larva grow into adults and exit the tree. When they do this, they form capital D-shaped exit holes in the bark.
- Heavily infested trees may attract woodpeckers, so keep an eye out for increased woodpecker activity on ash trees.
How to report a suspected infestation:
- If you think you’ve found an EAB infestation, submit a report to the Oregon Invasive Species Hotline.
- It’s important you provide as much detail as possible to assist the conservation specialists who will investigate your report. Take lots of photos that are well lit, in focus, and from several angles. Specialists may reach out to you with follow up questions about your report.
What happens once an infestation is reported?
Conservation specialists will follow up on reports to confirm if it’s an EAB infestation. Once confirmed, attempts will be made to contain the infestation. With landowner permission, an infested ash tree may be cut down and chipped to kill the EABs living in the tree. It’s possible that nearby trees will also need to be removed to protect other ash trees in the area.
Agencies responding to the appearance of EAB are in the process of developing a plan for handling the affected wood. It is possible wood chips can be processed and put to other uses such as landscaping, trail surfaces, composting, livestock bedding material, or lumber products.
How can I protect my ash trees?
The emerald ash borer only affects ash trees. Residents should walk around their yards and neighborhoods to take stock of the ash trees present and decide which trees are worth trying to save.
Specialized insecticides can be applied to protect individual trees not already infested. Depending on the tree size and situation, a single treatment costs around $200-$300 and needs to be reapplied every 2-3 years. Pesticides may sometimes work on infested trees, if discovered early. Residents should work with an ISA-certified arborist to pursue this option.
Read more about preventive chemical treatments here.
At this time, residents do not need to remove ash trees from their property. It is better to wait until more information is available about the extent of EAB’s presence in the Portland metropolitan area.
More resources:
Washington County residents can reach out to our Forest Conservation Specialist, Brandy Saffell, with questions about managing EAB on their property.
- Website – Oregon Invasive Species Council Emerald Ash Borer
- USDA StoryMap – An Overview of EAB
- Document – EAB Readiness and Response Plan for Oregon
- YouTube Video – Identifying the Emerald Ash Borer
- YouTube Video – Saving Oregon Ash
- YouTube Video – An introduction to the EAB for Kids
- Article – Breeding Ash Trees for EAB Resistance