Emerald Ash Borer

We are proud to have received funding from the Western Integrated Pest Management Center (project CO020) to support a Regional Education and IPM Implementation Program focused on managing emerald ash borer in urban landscapes. This website provides up-to-date information relevant to the states involved in our project, with contributions from collaborators at Oregon State University, Utah State University, Montana State University, and the University of Wyoming.

Important resources

Insects that resemble emerald ash borer

Identifying ash trees

Emerald ash borer feeding injuries

Emerald ash borer information network

Oregon EAB invasive species alert

EAB overview: recorded presentation

General information on emerald ash borer (EAB)

Emerald ash borer in the west: what to know

How to identify emerald ash borer and symptoms of infestation

What to do if you suspect emerald ash borer

Management and treatment options

Where to report

WIPM grant collaborator resources

Helpful websites and publications

Please visit the emerald ash borer webpage for information on the pest description, life history, and management.

Emerald ash borer in the west: what to know

The emerald ash borer (EAB) is a highly destructive, invasive beetle that targets ash trees. Since its first detection in Michigan in 2002, EAB has spread rapidly across North America, killing tens of millions of ash trees in forests, urban landscapes, and residential areas.

Ash trees are valued in the western United States for their drought tolerance, shade, and ecological benefits. Unfortunately, EAB poses a serious threat to these trees. Larvae tunnel beneath the bark, disrupting the tree’s ability to transport water and nutrients. Without intervention, infested trees typically die within 3 to 5 years.

Why it matters

The consequences of EAB infestation are far-reaching:

Economic impact: tree removal, replacement, and treatment are costly for homeowners, municipalities, and park systems.
Ecological disruption: the loss of ash trees reduces biodiversity and alters habitat for wildlife.
Urban heat and aesthetics: fewer trees means less shade, higher urban temperatures, and diminished neighborhood character.

Current presence in the west

Emerald ash borer continues to expand its range across North America. In the western U.S., its presence varies by state:

Colorado: first detected in Boulder in 2013; now confirmed in multiple counties
Oregon: detected in 2022, with active monitoring and quarantine zones
Montana, Utah, Wyoming: no confirmed detections as of now.

Early detection and proactive management are critical to slowing its spread and protecting valuable ash tree populations.

Tracking and tools

To explore EAB’s spread in more detail, several interactive tools are available:

Colorado

View detections by year on the Colorado State Forest Service map.

Oregon

See current detections and quarantine zones on the Oregon Department of Agriculture map. Oregon also offers a degree-day model to predict EAB adult emergence and egg-laying periods, helping guide surveillance and management decisions. A similar tool is also managed by the USA National Phenology Network.

National overview

For a broader view of EAB’s distribution across North America, visit the EAB Information Network map.

These tools are essential for tracking EAB’s movement and planning timely responses in areas at risk.

How to identify emerald ash borer and symptoms of infestation

Accurate identification of both ash trees and the emerald ash borer beetle is essential for effective monitoring, management, and prevention of infestation.

Identifying ash trees

Before identifying EAB, it’s important to confirm that the tree in question is an ash. Key characteristics of ash trees include:

Leaves: compound leaves with 5–11 leaflets arranged in pairs along a central stem, often with a single leaflet at the tip. Leaflet edges may be smooth or slightly toothed.
Bark: gray bark with a diamond-shaped pattern on mature trees; smoother on younger trees.
Branching: opposite branching pattern—branches and buds grow directly across from each other.
Tree shape: typically, oval or rounded canopy with a straight trunk.

For more help, see ash tree ID guides from Colorado State University and Oregon State University.

Ash tree leaves

Image credit: Robert Vidéki, Doronicum Kft., Bugwood.org

Ash tree bark

Image credit: Paul Wray, Iowa State University, Bugwood.org

Ash tree with branches opposite one another

Ash tree opposite branching

Image credit: City of Aurora, Colorado

Ash tree shape and trunk style

Image credit: David Cappaert, Bugwood.org

Identifying emerald ash borer

EAB can be identified in both its adult and larval stages:

Adults are slender and elongated beetles, measuring approximately ½ inch long and ⅛ inch wide, with a metallic emerald green exterior and a coppery-red underside. They are active during the summer months and leave behind distinctive D-shaped exit holes in the bark as they emerge.
Larvae are cream-colored and feature distinctive bell-shaped body segments; when fully developed, they can grow up to 1½ inches long and create winding, S-shaped feeding galleries beneath the bark.

For help distinguishing EAB from similar species, see comparison guides from Colorado State University and Oregon State University.

Adult emerald ash borer

Image credit: Pennsylvania Department of Conservation and Natural Resources, Bugwood.org

Larva of emerald ash borer

Image credit: David Cappaert, Bugwood.org

Symptoms of infestation

Early detection is critical. Look for these signs, especially in combination:

Canopy dieback: progressive thinning or death of branches, typically starting at the crown and moving downward.
S- or serpentine-shaped markings: present under bark, caused by larvae moving and feeding. Galleries are filled with frass, or larval excrement.
Epicormic shoots: unusual sprouting from the trunk or base, often a stress response.
Bark splitting: vertical cracks may form as the tree attempts to grow tissue around larval galleries.
D-shaped exit holes: characteristic marks lest by emerging adult beetles
Increased woodpecker activity: birds feeding on larvae beneath the bark may indicate infestation.

Note: These symptoms can resemble those caused by other pests or diseases. Multiple signs together are more indicative of EAB.

See Colorado State University and Oregon State University resources for diagnostic photos and further guidance.

Ash trees with canopy thinning

Image credit: Ryan Armbrust, Kansas Forest Service, Bugwood.org

S-shaped markings under bark of ash tree

S- or serpentine-shaped markings under ash tree bark

Image credit: Joseph OBrien, USDA Forest Service, Bugwood.org

Epicormic shoots emerging from ash tree trunk

Image credit: Pennsylvania Department of Conservation and Natural Resources – Forestry , Bugwood.org

Split bark on ash tree with emerald ash borer gallery underneath

Bark splitting on ash tree

Image credit: Joseph OBrien, USDA Forest Service, Bugwood.org

D-shaped exit hole from adult emerald ash borer emerging from ash tree with a pencil for size scale

D-shaped adult exit hole with pencil for scale

Image credit: Kenneth R. Law, USDA APHIS PPQ, Bugwood.org

Ash tree with holes from woodpecker feeding

Ash tree with woodpecker flecking

Image credit: David Cappaert, Bugwood.org

What to do if you suspect emerald ash borer

Step 1: Confirm identification

Before taking action, make sure the tree in question is an ash and that symptoms match those of EAB.

Use identification guides for ash trees and EAB feeding injuries from Colorado State University and invasive species information from Oregon State University.

Refer to the symptoms listed in the How to identify emerald ash borer and symptoms of infestation section for visual and behavioral clues.

Step 2: Report the infestation

If you suspect EAB, report it to the appropriate agency in your state:

Colorado

Contact your local CSU Extension office, city or county division of forestry, or the Colorado State Forest Service (CSFS).

Oregon

Report sightings to the Invasive Species Hotline.

Montana

Reach out to your local extension agent, the Schutter Diagnostic Lab at Montana State University, or the Montana Department of Agriculture.

Utah

Contact the Utah Plant Pest Diagnostic Lab or the Insect and Pest Program at the Utah Department of Agriculture and Food.

Wyoming

Notify your local county extension office or the Wyoming Department of Agriculture. You may also submit detection information to USDA-APHIS.

Step 3: Take action

Once EAB is confirmed, consult a professional to determine the best course of action:

Hire an ISA-certified arborist to assess the tree and recommend treatment or removal.

Avoid do-it-yourself removal, especially for large or heavily infested trees—this can be dangerous. Note that canopy dieback of 30% or more means that a tree is no longer safe for an arborist to climb for removal.

If removal is necessary, dispose of wood properly. Shred wood into chips smaller than 1 inch to prevent EAB survival and follow local disposal guidelines to avoid spreading the pest.

Helpful Tools

Boulder County Decision Guide for treatment vs. removal

Oregon State University Guide to Hiring Pest Control Companies

Your local extension office can assist with planning and referrals: Colorado, Oregon, Montana, Utah, Wyoming

Ash tree in shopping center parking lot with upper canopy dieback due to emerald ash borer damage

Ash tree with upper canopy dieback

Image credit: Ada Szczepaniec, Colorado State University

D-shaped exit holes

Image credit: Daniel Herms, The Ohio State University, Bugwood.org

Serpentine carvings on tree due to emerald ash borer

Ash tree with serpentine galleries caused by EAB larvae

Image credit: Edward Czerwinski, Ontario Ministry of Natural Resources, Bugwood.org

Emerald ash borer emerging from ash tree

EAB adult emerging from tree

Image credit: Jared Spokowsky, Indiana Department of Natural Resources, Bugwood.org

Management and treatment options

Homeowner recommendations

EAB is present in parts of the western U.S., making regular monitoring and proactive care essential. Here’s how you can protect your ash trees:

Monitor trees

Identify ash trees on your property using guides from Colorado State University and Oregon State University.
Inspect regularly for signs of an emerald ash borer infestation: canopy dieback, epicormic shoots, D-shaped exit holes, serpentine galleries, and woodpecker activity.

Prevent spread

Never move firewood from infested areas. Buy firewood locally at your destination.
Diversify your landscape with a mix of tree species to improve resilience.

Stay informed by following local updates and resources:

Colorado: Denver Extension, City of Fort Collins, Colorado State Forest Service, Boulder County

Oregon: Solve Pest Problems, Emerald ash borer in Oregon, Oregon Invasive Species Council, City of Portland

Montana: Urban IPM EAB site, Montana EAB Field Guide

Utah: Utah State University Extension

Wyoming: Cheyenne Urban Forestry, University of Wyoming

Treatment strategies

Insecticide information

Before applying any insecticide, consult an ISA-certified arborist to assess your tree’s health and determine the most effective and safe treatment plan.

Multiple studies, including long-term research from Michigan State University (Bick et al. 2017 and McCullough et al. 2018), have shown that emamectin benzoate, applied via trunk injection, is the most effective insecticide for controlling emerald ash borer. It significantly reduces larvae and exit holes, with protection lasting up to 2–3 years, even in high-pressure infestations.

Dinotefuran, applied via basal trunk spray, is moderately effective and acts quickly due to its high solubility and fast translocation. Imidacloprid, typically applied as a soil drench, is less effective—especially for larger trees (over 30 cm DBH) or in areas with many untreated ash trees. Even high-dose applications may result in up to 30% canopy loss.

Azadirachtin, a botanical insecticide, may be useful in low-density infestations. It disrupts egg viability in older females and eventually kills larvae, though its effects are slower and less consistent.

Neonicotinoids like imidacloprid are easier and more cost-effective to apply, particularly as soil drenches, but their performance is inconsistent—especially for larger trees over 30 cm in diameter at breast height (Smitley et al. 2010). High-dose applications may offer some protection, yet many treated trees still experience up to 30% canopy loss (Smitley et al. 2015). Treatment success is highest when initiated early, repeated at recommended intervals, and when surrounding ash trees are also treated to reduce reinfestation pressure.

Work with professionals

Managing EAB requires specialized knowledge and equipment. Do not attempt to treat or remove infested trees on your own.

Hire an ISA-certified arborist to assess tree health and recommend a treatment or removal plan.
If removal is necessary, ensure wood is shredded into chips smaller than 1 inch to prevent EAB survival.
Consider removing young ash trees if you prefer not to oversee a long-term treatment plan.

Resources like Boulder County’s decision guide and considerations for hiring a contractor can help you make informed choices.

Why management matters

Tree health and safety: EAB disrupts water and nutrient flow, leading to tree death and potential hazards from falling limbs.

Environmental impact: Ash trees provide shade and habitat. Their loss affects local ecosystems and urban canopy cover.

Economic costs: Treating or removing infested trees can be expensive for homeowners and municipalities.

Preventing spread: Timely management helps protect neighboring trees and public green spaces from infestation.

Resources and support

Reporting EAB by state

Colorado

Contact your local Colorado State University extension office, your city or county division of forestry, or the Colorado State Forest Service.

Oregon

Report the finding to the Invasive Species Hotline.

Montana

If you suspect EAB on your property or have a suspected EAB insect sample, contact your local extension agent, the Schutter Diagnostic Lab at Montana State University, or the Montana Department of Agriculture.