Emerald Ash Borer – How concerned should I be?

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On Monday July 11th 2022 the Oregon Department Of Forestry, Oregon Department of Agriculture, and Portland area news stations released findings that the first known specimen of emerald ash borer (EAB) had been found in Forest Grove. While we knew that this was inevitable, it still sent shockwaves through the local arboriculture community. The potential danger that EAB now poses for all species of ash trees west of the Rocky Mountains cannot be understated.

WHAT IS EMERALD ASH BORER?

Emerald ash borer is an invasive beetle from northeast Asia. It was first found in North America in Michigan and Ontario in 2002. Unlike the ash trees of its native habitat their North American counterparts have little to no natural immunity or defense against EAB.

Over the past 20 years EAB has spread through 35 states in the U.S. and 4 provinces in Canada decimating populations of native and ornamental ash. Five species of native ash are now on the critically endangered list and it’s estimated that EAB has killed over 100 million trees since its arrival.

Until last week’s news came out, the closest known infestation of EAB had been in Colorado–safely contained by the natural barrier of the Rockies. Now that EAB has been found in Oregon its spread through the western states is only a matter of time.

HOW TO IDENTIFY EAB

Adult EAB are metallic green beetles with red bodies under their wings. They are 3/8-1/2″ long with flat heads and large bulging eyes. There are several other species of beetle in the Pacific Northwest that look similar to EAB, so the Oregon Department of Agriculture has put together this visualization to help with identification.

The larvae of EAB tunnel through the cambium layer of the tree cutting off the tree’s flow of nutrients. The tunnels, called galleries, are serpentine in shape and can be easily recognized when the bark is removed. The larvae will live under the bark for about a year before emerging as mature beetles in the late spring when they move on to reproduce in the next tree. It’s estimated that they have a range of up to 30 miles when the adults emerge.

Signs of EAB activity include dieback or thinning of the upper canopy, excessive output of epicormic sprouts (also called “suckers”), and damage from woodpeckers as they feed on the EAB larvae. These symptoms can also be caused by other environmental factors making it important to have your trees assessed by a trusted professional arborist.

If you have a confirmed sighting of EAB please go to this website to report it to the Oregon Invasive Species Council.

HOW DO I KNOW IF MY TREE IS AN ASH?

Ash trees (genus Fraxinus) can be most easily identified by their branching structure and leaves. All ash have an opposite branching structure where branches emerge in pairs directly across from one another. They are one of only four genera of common trees with opposite branches (ash, maple, dogwood, and horsechestnut) with most other trees displaying an alternate branching structure.

Ash also have oppositely arranged compound pinnate leaves. The pinnate leaves emerge along the “stem” in pairs with one terminal leaf at the very end. There can be anywhere from 5 to 11 leaves per “stem” depending on the species. The leaves are ovate in shape, coming to a point on either end.

While the native Oregon Ash (Fraxinus latifolia) is the most common ash found in our forests, many cultivars of green and white ash have been planted as street and ornamental trees. It’s important to note that EAB is equally detrimental to all ash species. If you aren’t sure if you have ash trees on your property, you can call General Tree Service at the number listed at the bottom of this article and we’ll send an arborist out to identify and assess your trees.

WHAT CAN I DO NOW?

The bad news: There is no way to reverse damage done by EAB once it’s in your tree.

The good news: General Tree Service has consulted local and national experts and publications to put together a prevention program that will give your trees the best chance of survival. Our treatment program can be tailored to your landscape and includes an inoculation that can be combined with additional soil and nutritional care to keep your trees healthy.

While the preservation of the Oregon Ash in our forests falls to the Department of Forestry and the Department of Agriculture, it’s our responsibility as private citizens to ensure the longevity of trees on our properties. To speak with an arborist about caring for your trees call General Tree Service at (503) 461-6535.

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