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.

The adult beetles nibble on the foliage of ash trees but cause little damage. 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.

Emerald Ash Borer 2025 Update:

First found in Oregon in 2022 at a school in Forest Grove, this summer the insect showed up in traps in five new areas, all within the existing EAB quarantine boundary:

• Hazeldale Park about a mile west of Beaverton
• Killin Wetlands Nature Park near Banks in western Washington County
• 5 miles northwest of the town of Yamhill in Yamhill County
• Three miles southeast of Oregon City in Clackamas County
• On Bureau of Land Management land east of Scotts Mills in Clackamas County

While it’s possible EAB could turn up in more traps when they are checked in September, Williams said most adults will have finished their short life cycle, laid their eggs, and died by October or November. 

City Response and Treatment Plan

The city's EAB response primary goal is to preserve Ash canopy and to prevent EAB spread for as long as possible. Since EAB was first detected three years ago, we have been preparing for its spread beyond Forest Grove.

Hillsboro is protecting our ash trees by treating approximately 500 healthy public ash trees along the western and southern city boundary. This will create a buffer zone from current outbreaks as a phase one response plan.

A comprehensive tree inventory is also underway that includes public and right-of-way trees. Data collected from this ongoing effort will help locate all ash tree populations and inform the city’s additional EAB response plan phases.

The phased approach is adaptive to current outbreak information; the phased map and timeline is subject to change to reflect city needs and resources available.

What can you do?

1) Take Care of your Ash Trees 

If you have ash trees on your property, take care of them. Emerald Ash Borer (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. 
• 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 

• Community members with private trees (in good health and over 6") are encouraged to contact a tree care company to plan a preventative treatment of emmimectin.
• 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.
• 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 inches in diameter. Small trees that cannot be treated are recommended to be replaced.

3) Do Not Move Firewood! 

To slow the spread of Emerald Ash Borer, 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 Dontmovefirewood.org.

4) Assist with EAB Detection

• Use the resources provided below and local training opportunities to learn how to identify ash trees and the emerald ash borer. 
• 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. 

Report EAB in Hillsboro

If you observe EAB please report your findings to Urban Forestry via the form below.

Report EAB Activity

If you are able, please photograph any evidence and document the exact location of perceived EAB sighting. Photographs should include declining canopy, epicormic growth, D-shaped exit holes, S-shaped galleries, and bark shedding or splits.

Images can be emailed to our Urban Forester, Lisa Renee Wilson at lisa.wilson@hillsboro-oregon.gov.

Emerald Ash Borers in Oregon

The Oregon Department of Forestry warns that the establishment of Emerald Ash Borers 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 draining and where seasonally high water tables can exclude other tree species. 

Oregon ash (Fraxinus latifolia), 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, including: white ash (F. americana), flowering ash (F. ornus), Raywood ash (F. oxycarpa), green ash (F. pennsylvanica), European ash (F. excelsior), black ash (F. nigra), and velvet ash (F. velutina). 

The loss of ash trees caused by Emerald Ash Borer 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.