Emerald Ash Borer

Emerald Ash Borer in Oregon

The emerald ash borer, Agrilus planipennis, is a destructive, invasive beetle that infests and kills ash trees (Fraxinus spp.). It was first discovered in the U.S. in 2002 in southeastern Michigan and has since been detected in more than 30 states, including Oregon (Forest Grove) in June 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 the following counties:

Clackamas
Marion
Multnomah
Washington
Yamhill

A permanent quarantine is now in effect for these counties, triggering specific restrictions. Tree materials from ash, olive, and white fringe tree, must remain within quarantined counties (Washington, Yamhill, Marion, Clackamas and Multnomah). Wood waste must be processed and disposed of accordingly.

Visit the Oregon Department of Agriculture, for specific quarantine details and restrictions, including:

Regulated materials
Treatment options for regulated materials
Timing for removal and pruning

Why it Matters

EAB adults lay their eggs on ash trees, and after hatching, the larvae burrow under the bark to feed on the tree, eventually cutting off its supply of water and nutrients. All species of ash in Oregon are susceptible to EAB, in both urban and natural environments. Once an ash tree becomes infested, the tree will die over the course of three to seven years.

Oregon ash (Fraxinus latifolia) is an important native tree that grows along rivers, streams, and wetlands in low-elevation areas, including throughout the Willamette Valley. It is a critical source of shade, erosion control, pollution filtration, and wildlife habitat. Many other ash species are commonly planted in yards, parks, and along streets all over Oregon, including in Lake Oswego.

Losing ash trees will have wide-reaching effects on Oregon's environment and economy. Large, healthy trees make communities more resilient to heat, pollution, and natural disasters. Dead and dying trees pose a risk to life and property. Responding to EAB is costly and will impact local economies. However, proactive planning and management can help save money, time, and hardship in the long run.

Management Strategies

Ash trees become extremely brittle as they die and can be hazardous to people, property, and infrastructure as their risk of failure increases. Methods for managing ash trees before they become hazardous include:

Removal and Replacement
Insecticide Treatment

Visit Oregon EAB to learn more about these management strategies.

In Lake Oswego, management options for ash trees also include treatment or removal/replacement. Tree removal permits may be required.

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. Replace or Treat your Ash Trees

Property owners are responsible for the care and maintenance of trees located on their property as well as any trees in the right-of-way adjacent to their property.

Community members with private trees (in good health and over 6 inches (6") in diameter) are encouraged to contact a tree care company to plan a preventative treatment. Insecticide treatments can be an effective way to protect ash trees from EAB and keep them alive for the rest of their natural lifespans. When properly applied by a trained and licensed pesticide applicator, insecticide treatments can be up to 95% effective.
Spring and Fall are the best times to treat.
Preventative treatment is better to provide less stress to trees.
Stressed trees are more vulnerable and you must treat prior to 20% infection (die back) for the best chance of success.
A single round of Ash treatment lasts two years and is the most sustainable and budget-friendly option.
EAB can never be eradicated from an area once it is established, therefore, ash trees will need to be treated every 1 to 3 years to continue protect them from an EAB infestation.
The most effective treatment is an emamectin benzoate trunk injection. Application requires specific tree injection training and a pesticide applicator license, and should be applied after leaf emergence in the Spring to avoid pollinator impact or soil leaching.
Trees that respond best to treatment will be those greater than 6" in diameter (DBH), measured a breast height - 4.5 feet from the ground. Small trees that cannot be treated are recommended to be replaced.
The City of Lake Oswego requires tree removal permits for trees 6” in diameter or larger. If you would like to request removal of a tree 6” in diameter or larger, please visit the City's tree website - www.lakeoswego.city/trees - for applications, or contact Planning staff at trees@lakeoswego.city or 503-635-0290 for assistance.

3. Do Not Move Firewood!

The EAB have largely been spread through the movement of infested 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 and get additional resources at www.dontmovefirewood.org.

4. 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 taking proactive steps to stay ahead of the Emerald Ash Borer (EAB) infestation. For information on what is happening in the City’s parks and open spaces, visit the Parks webpage.

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.

Two helpful resources on recognizing ash trees include: