Frequently Asked Questions About Emerald Ash Borer In Oregon

By Kristin Ramstad, ODF Urban and Community Forestry Assistance Program (Jim Gersbach, ODF Public Affairs, contributed to this article)

As almost everyone has heard by now, the invasive and destructive pest, emerald ash borer (EAB) has been detected recently in the city of Forest Grove in Washington County. This article seeks to answer some of the questions city officials and staff may have about the pest and how they should prepare for it.

What’s the Big Deal about EAB?

Although ash trees are not one of the most common urban trees in Oregon, tens of thousands of beautiful, large, non-native ashes are growing in parks and yards and along streets statewide. The experience in other states shows that up to 99% of all ash trees in cities and towns die within a few years of the arrival of emerald ash borer. We expect the same will be true in Oregon. Tree loss on this scale will be expensive for many cities to deal with and momentous at a time when communities are trying to increase tree canopy to reduce urban heat and improve the mental and physical health of their residents. However, the biggest impact of EAB will likely be along Oregon’s rivers and streams. Research shows that Oregon’s native ash (Fraxinus latifolia) is highly susceptible to emerald ash borer. The experience in other states shows that almost the entire wild ash population is wiped out once emerald ash borer arrives. The same devastation is expected in the Pacific Northwest. Oregon ash plays a vital role in the wetlands and rivers where it prefers to grow. It’s canopy shades streams, helping keep water cool for fish. Its extensive root system helps reduce erosion along streams. Many birds, animals and insects eat the seeds and leaves. So, the loss of the tree will harm our native forest ecosystems.

Will the State of Oregon be attempting to eradicate this outbreak?

The 16 ash trees initially found to be infested with emerald ash borer were promptly cut down and properly disposed of. However, it’s evident that the insects had been in the area for at least a couple of years prior to discovery. Given the distance female emerald ash borers can fly, it is almost certain that this pest has spread too widely to eradicate. Over the course of two decades, no state out of 35 has succeeded in eradicating emerald ash borer once it was detected in their area. The focus now is on preventing people from spreading it farther and faster than it would naturally travel. One way all of us can slow the spread of this pest is by not moving firewood beyond the local area where it is cut.

What does the State of Oregon recommend cities do about EAB at this point?

First, cities should avoid planting any more ash trees given the presence of emerald ash borer in the state. We recommend cities and towns with approved street tree lists eliminate the ash trees from them, as has already been done in several Oregon cities. Second, find out how many trees in your city are ash and where they are located. The Oregon Department of Forestry has tree inventory software1 it can make available to cities for free for this purpose. Next, among your city’s ashes, determine the healthy large trees that should be treated to keep them from getting infested, and map the trees that are already unhealthy. Third, if EAB has not yet been detected in your area, focus your city’s efforts on preparing for an infestation. Your town should consider both how it will treat and preserve its large healthy ash, and how it will remove and store the infested wood from dead trees until it can be properly disposed of. Please do not move the wood more than about 10 miles in any direction area to avoid spreading the insect faster than it could spread naturally! Generally, the guidance is that if the pest has been detected 25 miles away, your town should be on “high alert” and be ready to start its EAB treatment on important ashes. Once the pest is detected within 15 miles of your city, begin treating those designated trees. Since experience shows that heavily infested trees

1 To find out more about Tree Plotter Inventory software, please send an email to urbanforestry@odf.oregon.gov, with “TPI interest” in the subject line.