Emerald Ash Borer

What is an Emerald Ash Borer?

Emerald ash borer, Agrilus planipennis, is a beetle that was first discovered in the U.S. in 2002 in southeastern Michigan. It has since been detected in more than 30 states, including Oregon (Forest Grove), on June 30, 2022. This was the first confirmation of the invasive pest on the West Coast. 

While the emerald ash borer (EAB) has not been detected within the City of Lake Oswego, it has been detected in Clackamas County as well as Washington, Yamhill and Marion Counties. These counties are currently under quarantine. Quarantine prohibits materials from all plant parts of ash (Fraxinus spp.), white fringetree (Chionanthus virginicus spp.), and olive (Olea spp.) trees from movement outside these counties. 

Emerald Ash Borer in Oregon

The adult beetles nibble on the foliage of ash trees but cause little damage. However, the larvae (the immature stage) feed on the inner bark of ash trees, disrupting the tree's ability to transport water and nutrients. The invasive beetles have largely been spread through the movement of infested firewood.

The Oregon Department of Forestry warns that the establishment of EABs will likely devastate ash woodlands and riparian zones where native Oregon ash (Fraxinus latifolia) is a dominate species. These trees provide important shade, food and habitat resources in riparian areas where soils can be poorly drained and where seasonally high-water tables can exclude other tree species. 

Oregon ash, a member of the olive family (Oleaceae), is one of 16 species of ash in the United States. It is the only ash species that is native to the Pacific Northwest; however, ornamental ash species from other parts of the country and world are commonly used in landscaping in Lake Oswego, including: white ash (F. americana), flowering ash (F. ornus), Raywood ash (F. oxycarpa), green ash (F. pennsylvanica), European ash (F. execelsior), black ash (F. nigra), and velvet ash (F. velutina). 

The loss of ash trees caused by EAB infestations could lead to a reduction in urban tree canopy, an increase in invasive plants taking hold within our community, and loss of shade and habitat along streams, to name just a few of the anticipated impacts.

What can you do?

1.  Take Care of your Ash Trees 

If you have ash trees on your property, take care of them. The EAB is most attracted to trees that are stressed.

• Water your trees in the dry months and maintain a layer of woodchips or mulch around the base of your trees. One of the main stresses for a tree can be summertime drought, and these measures will help maintain adequate water in the soil near the tree. Visit the Lake Oswego Tree Care and Maintenance Archives for a Spring 2023 article on “Supplemental Watering and Mulch to Prevent Drought Stress” 
• Avoid pruning, especially during high EAB activity (April through October). Pruning can send signals to insects that a tree is in stress. If you do need to prune your ash tree, hire a professional arborist to ensure pruning is done properly. A professional arborist can also provide guidance on other things you can do to improve the health of your trees. 
• If planting new trees on your property, carefully inspect plant materials before purchasing. Avoid planting new ash trees. 

2.  Do Not Move Firewood! 

To slow the spread of the EAB, it is important to not transport firewood or wood products. Insects and diseases, which can be microscopic and undetectable to the eye, can move much faster and farther by people transporting firewood and wood products than they can on their own.

• Buy or obtain your firewood as locally as possible (within 10 miles or less is best. 50 miles is too far). 
• Even moving firewood from one town to the next town could provide EAB with a free ride.
• Learn more at www.dontmovefirewood.org.

3.  Assist with EAB Detection

• Use the resources provided below and local training opportunities to learn how to identify ash trees and EAB. 
• Report observations of EAB or trees with symptoms by reporting online to the Oregon Invasive Species Online Hotline. 
• Enroll in OSU Extension's Oregon Forest Pest Detector Program to learn more about recognizing and reporting signs and symptoms of high-priority, invasive forest pests like EAB. 

What is the City doing?

The City follows Oregon's Emerald Ash Borer Readiness and Response Plan (March 2021) and it's recently approved/updated Urban and Community Forestry Plan (UCFP). The UCFP brings together the policies, practices, codes and documents relating to tree management in the city and includes actions items to more effectively manage and maintain the City’s urban forest. There are several actions recommended in the UCFP that will help the City address EAB and other emerging pests, such at the Mediterranean oak borer (Xyleborus monographus). Recommended actions include:

• Conducting a comprehensive tree inventory
• Creating a pest management action plan
• Continuing public education programs

In addition:

• The Parks & Recreation Department is working with the Clackamas County Soil and Water Conservation District to monitor EAB traps throughout the city.
• In 2023, the Parks Department treated 28 ash trees at Foothills Park as a preventative for EAB.
• Following the January 2024 winter storm, the Parks Department has been conducting tree risk assessments in natural areas to identify and manage high and extreme risk trees and to monitor others on a periodic basis.
• Staff from the Parks, Planning and Public Works Departments are continuing to receive training on identification and best practices related to EAB and other emerging pests.
• The City has offered a number of public education opportunities including a free public workshop on EAB preparedness and numerous articles in city-wide publications.

Identification

Identification - Emerald Ash Borer

EAB is a small metallic-green buprestid, or jewel beetle, that bores into ash trees, feeding on tissues beneath the bark, ultimately killing the tree. The Emerald Ash Borer is capable of infesting all ash trees in the genus Fraxinus. 

It is more likely you'll notice tree stress before you notice the beetles. Symptoms of EAB include:

• Crown thinning or dieback from the top of the tree
• New shoots sprouting from the base or trunk of the tree below the main crown
• Cracks or separation of bark from the trunk
• Light patches of bark from woodpecker shaving

Signs of EAB include:

• D-shaped exit holes are ⅛ inch wide
• Adult EAB beetles, measuring ⅜ to ½ inch long; slender, bullet shaped body; entirely green; smooth without ridges, hairs, bumps. When in flight (wings raised), the abdomen is bright coppery-red. Adults emerge from trees and are typically present from June through August; larvae are under bark and in sapwood most of the year.
• Long, skinny larvae within feeding galleries
• Serpentine feeding galleries under bark

Note that signs and symptoms of drought, other insects and diseases may be confused with or co-occur with EAB infestations. There are a lot of bright green insects that are native to Oregon, and many may be found on or around trees. Use this chart to help distinguish Emerald Ash Borer from other shiny green bugs. 

Identification - Ash Trees

The EAB is known to infest all species of ash (Fraxinus spp.), which can be easily recognized by their compound leaves and opposite branching pattern. To properly identify ash trees, use the following criteria: 

Branch and Bud Arrangement

Pull down a branch of the tree and look at the branches. All species of ash trees have opposite branching, meaning that the branches originate and extend out from the same point along the stem. Keep in mind that some branches may die and fall off, so not every singles branch will have an opposite mate, but the overall pattern of branching will be opposite. 

Leaves

Now that you've established opposite branching, take a look at the leaves. All ash trees will have pinnately compound leaves composed of 5-11 leaflets. Each leaf will have an odd number of leaflets, with lateral leaflets in pairs opposite one another and a single terminal leaflet at the top. The leaflet margins may be smooth or toothed depending on the species. 

Bark

Mature ash trees have rough bark with diamond shaped ridges. On young ash trees, bark is relatively smooth. 

Seeds

Ash trees have winged, oar-shaped seeds known as samaras that occur in clusters and typically hang on the tree until late fall or early winter. Samaras only appear on female trees, while male trees have clustered flowers but no samaras.

Oregon Ash

Mature Oregon ash attain heights of 60 to 80 feet with a diameter at breast height of 16 to 30 inches. Ash may live at least 250 years. In forest stands, Oregon ash develop short, narrow crowns with small branches on long, straight boles. Open-grown trees have broad, rounded crowns with large limbs on short boles. The root system of ash is moderately shallow, wide-spreading, and densely fibrous.

Visit OSU Extension Service webpage on recognizing ash trees to learn more. 

Emerald Ash Borer Quarantine Alert

In August 2024, the Oregon Department of Agriculture issued a permanent quarantine across Washington, Yamhill, Marion and Clackamas Counties. 

Quarantine prohibits materials from all plant parts of ash (Fraxinus spp.), white fringetree (Chionanthus virginicus), and olive (Olea spp.) trees from movement outside Washington, Yamhill, Marion, and Clackamas Counties.  

In response to the discovery of emerald ash borer (EAB), the Oregon Department of Agriculture (ODA) has adopted an EAB permanent quarantine (control area) as per Oregon Administrative Rule (OAR 603-052-1075), limiting the movement of ash, white fringe, and olive tree materials​ from Washington, Yamhill, Marion, and Clackamas Counties. The purpose of the quarantine is to slow the spread of EAB by restricting the movement of host tree materials to unaffected locations in the state. EAB is now considered the most destructive forest pest in North America, killing hundreds of millions of ash trees. 

The EAB quarantine restricts the movement of ash, white fringetree, and olive tree materials including but not limited to logs, green lumber, nursery stock, scion wood, root stock, chips, mulch, stumps, roots, branches, and firewood of any hardwood species. Exceptions to move nursery stock and wood materials of restricted species out of the quarantine area require a compliance agreement with ODA. Please view the links below for FAQs.

ODA is establishing several processing and disposal resources in the area to limit the movement of ash, white fringe, and olive tree materials within the quarantine area. For processing and disposal resources, please view the list below.

• ​Permanent EAB Quarantine Flyer.pdf
• ​List of disposal resources

Treatment

EAB is currently an unstoppable pest, but treatments are available to slow or prevent ash tree death. Insecticide treatments can be an effective way to protect trees from EAB either before they are infested or when infested trees have less than 20% canopy decline. However, it is important to understand that treatments to prevent damage from EAB must be repeated every two to three years to remain effective. Treatments are typically reserved for the most high-value ash trees. 

Pollinators and other “nontarget” organisms may be at risk from insecticides applied as cover sprays due to the risk of drift. North American ash species are wind-pollinated, and timing of applications should not coincide with pollen production. Systemic insecticides are a much lower risk to nontarget organisms that are not feeding on tree tissues. Research has shown that pesticide residues from systemic applications are not found in ash pollen. Systemic insecticides applied as liquid or granular soil drenches may negatively impact ground-nesting bees and other nontarget insects.

Tree Removal and Wood Disposal

If ash, white fringetree or olive tree species are pruned or removed, there are specific protocols that must be followed to dispose of the wood in accordance with quarantine restrictions. Avoid removing infested trees unless necessary during the EAB active period of April 1–September 30 to prevent the spread of live insects. Removal should be done during EAB’s dormant period, October 1–March 31. It is important to confirm that the tree service provider you are using knows about the quarantine and can properly handle the wood materials. ODA recommends the following practices for disposal:

• Chipping: Wood, brush, and stump grindings must be chipped or ground down to a size of no more than 1” in two dimensions (two of the three measurements- length, width, depth- must be 1” or smaller). Typical chippers used in tree care operations will not reliably create chips that meet this specification. Chippers equipped with a 1” screen will assure compliance.
• Debarking: At minimum, a complete removal of bark is required. The removed bark (and any removed wood) must be chipped down to a maximum size of 1” by 1” in 2 dimensions.
• Heat: Wood must be heated according to established pest or disease specific Best Management Practices. For regulated pests and diseases, the wood temperature must reach 160 degrees F for 75 minutes in the center of the piece.