Emerald Ash Borer
We have received funding from the Western IPM Center for a Regional Education and IPM Implementation Program for Emerald Ash Borer in Urban Landscapes. This website reflects up to date information on emerald ash borer applicable to states represented in our project group, which includes collaborators from Oregon State University, Utah State University, Montana State University, and the University of Wyoming.
Important resources
Please visit the emerald ash borer webpage for information on the pest description, life history, and management.
Biology and importance
The emerald ash borer is an invasive beetle that severely damages ash trees across North America. First found in Michigan in 2002, it has spread to other areas very rapidly (including Colorado and Oregon), killing millions of ash trees in forests, cities, and neighborhoods. EAB has not yet been detected in Montana, Utah, or Wyoming.
What does the beetle look like?
Larvae are white with characteristic bell-shaped body segments (see photo, below left); they burrow into the inner tree, then feed and create S- or serpentine-shaped patterns. Larvae will emerge as adults in spring, leaving D-shaped exit holes in trees. Adults are small, bright metallic green beetles with a copper/red underside and are approximately ½ inch long (see photo, below middle). They are active throughout the summer.
What are symptoms of infestation in ash trees?
Recognizing the symptoms of emerald ash borer infestation in ash trees is essential for several reasons, including early detection, ensuring safety and integrity of trees, and reducing costs of treatment or removal. It’s important to note that some symptoms may resemble those caused by other pests and diseases, so observing any of these in combination is particularly crucial to be aware of.
- Dieback of ash trees, or tree death of branches and twigs that starts near the tips and moves inward. This occurs in multiple branches and twigs, not just one. (See photo below at right — this is likely one of the first symptoms noticed)
- Excessive branching on tree trunks, also known as epicormic shoots
- S- or serpentine-shaped markings under tree bark
- D-shaped exit holes on the outer areas of trees
- Increased woodpecker activity (birds will attempt to eat larvae under the bark)
Why is emerald ash borer a problem?
Ash trees are very common and have been extensively planted in the Western United States due to their drought tolerance. Larvae feed under tree bark, disrupting water and nutrient flow, leading to severe tree damage and even death within 3 to 5 years if left untreated. Tree removal, replacement, and treatment can lead to huge economic impact for homeowners and cities. Loss of ash trees can disrupt local ecosystems and reduce shade cover.
Larva of emerald ash borer
Image credit: David Cappaert, Bugwood.org
Adult emerald ash borer
Image credit: Pennsylvania Department of Conservation and Natural Resources, Bugwood.org
Ash tree with upper canopy dieback
Image credit: Ada Szczepaniec
Where has emerald ash borer been found in the Western region?
Emerald ash borer has been detected in Colorado (as of 2013) and Oregon (as of 2022) and is currently undetected in Montana, Utah, and Wyoming. To learn more about where EAB is present throughout North America and the Western region, see this map maintained by the EAB Information Network.
Colorado
See this map, maintained by the Colorado State Forest Service, for EAB detections by year.
Oregon
See this map, maintained by the Oregon Department of Agriculture, for more information about EAB detections and quarantine. Oregon also maintains a website with degree-day model predictions to improve surveillance and containment of EAB. This model exists to provide decision-makers with accurate and timely forecasts of EAB adult emergence and egg-laying, helping guide decision-making related to surveillance and management. You can find a similar tool, managed by the USA National Phenology Network, at this link.
What should I do if I find emerald ash borer in my yard or a public ash tree?
Step 1: Make a positive identification of an emerald ash borer infesting an ash tree
Key characteristics of ash trees:
- See this file from Colorado State University for assistance with identifying ash trees.
- Leaves: ash trees typically have compound leaves, meaning each leaf is made up of multiple leaflets. These leaflets are usually arranged in pairs along a central stem, with a single leaflet at the tip. The edges of the leaflets can be smooth or lightly toothed.
- Bark: the bark of an ash tree is usually grey and can have a diamond-shaped pattern as the tree matures. Younger trees will have smoother bark.
- Branch and bud arrangement: ash trees have opposite branching, meaning the branches and buds grow in pairs directly across from each other.
- Overall shape: ash trees often have a rounded or oval shape with a straight trunk.
See resources from Colorado State University and Oregon State University for more help.
Key characteristics of emerald ash borer:
- Color: the adult emerald ash borer is emerald green, making it quite distinctive.
- Size: adults are about one-half to three-fourths of an inch long and about an eighth of an inch wide.
- Shape: the body is slender and elongated.
- Larvae: cream-colored with very distinct bell-shaped body segments. Their size varies as they grow but they will reach a length of about one and a half inches when fully grown.
See identification resources from Oregon State University for more help. Additionally, several look-alikes exist in the western region. See this compilation of similar species from Colorado State University and Oregon State University for help distinguishing EAB from similar species.
Key characteristics of an emerald ash borer infestation:
It’s important to note that some symptoms may resemble those caused by other pests and diseases, so observing any of these in combination is particularly crucial to be aware of.
- Dieback of ash trees, or tree death of branches and twigs that starts near the tips and moves inward. This occurs in multiple branches and twigs, not just one. (See photo below at right — this is likely one of the first symptoms noticed)
- Excessive branching on tree trunks
- S- or serpentine-shaped markings under tree bark
- D-shaped exit holes on the outer areas of trees
- Increased woodpecker activity (birds will attempt to eat larvae under the bark)
See resources from Colorado State University and Oregon State University for more help.
Step 2: Take action
Report the infestation
Make sure to share specific details about the location and signs of infestation and try to get a sample of the wood and the insect itself when you detect it.
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.
Utah
If you suspect EAB in Utah, contact the https://extension.usu.edu/pests/uppdl/index or the Insect and Pest Program at the Utah Department of Agriculture and Food.
Wyoming
Submit detection information to USDA-APHIS.
If the tree is in your yard, contact an International Society of Arboriculture (ISA) certified professional arborist in your area to discuss a plan of action. Due to safety concerns, it is not advised that you take matters into your own hands. If the infestation is in the earlier stages, insecticide treatments may be recommended to protect the tree. If the tree is heavily infested, removal may be necessary to prevent risk of injury. Note that canopy dieback of 30% or more means that a tree is no longer safe for an arborist to climb for removal. If a tree is removed from your yard, proper wood disposal is necessary. Shredding the tree into wood chips is an option, and research indicates that wood chips one inch or smaller cannot harbor EAB. Boulder County, Colorado has a helpful decision guide to aid you in determining an effective plan of action. Oregon State University has outlined helpful information about how to hire a pest control company. Your local extension agent or specialist (Colorado, Oregon, Montana, Utah, Wyoming) can also help.
Ash tree with upper canopy dieback
Image credit: Ada Szczepaniec
D-shaped exit holes, created by adult EAB as they emerge from ash trees
Image credit: Daniel Herms, The Ohio State University, Bugwood.org
Ash tree with serpentine galleries caused by EAB larvae
Image credit: Edward Czerwinski, Ontario Ministry of Natural Resources, Bugwood.org
Recommendations for homeowners
As emerald ash borer is present in our area, it is important to be aware of any infestations. Consider these steps.
Conduct regular monitoring of ash trees on your property:
Identification information listed above can help you determine if you have an ash tree in your yard. Regularly inspect your ash trees for signs of emerald ash borer, such as the characteristic dieback at tops of trees, excessive branching around tree trunks, D-shaped exit holes, serpentine galleries under tree bark, and increased woodpecker activity. Keep a regular watch over your own ash trees, being aware of their location on your property and overall health status.
Take preventative measures:
When using firewood for camping or other activities, avoid moving firewood or other ash tree materials from infested areas to prevent emerald ash borer spreading. Make sure to purchase firewood when you reach your destination. Consider planting diverse species of trees and shrubs to improve resilience of your landscape.
Work with professionals to treat or remove trees:
Contact an International Society of Arboriculture (ISA) certified professional arborist to help assess the health of your ash trees and come up with a best plan of action. If treatment is recommended, rely on professionals to apply systemic insecticides. These treatments are most effective when applied before a heavy infestation and must be applied at regular intervals thereafter (approximately every two years). If a tree is heavily infested and is past the point of being saved, it will likely need to be removed to ensure safety. Note that canopy dieback of 30% or more means that a tree is no longer safe for an arborist to climb for removal. Work with a professional arborist or tree removal service to safely remove and properly dispose of infested trees. If you have a young ash and don’t want to deal with long-term maintenance, consider cutting the tree while young. You can find more information here about how to seek help from a professional.
Stay informed of information on emerald ash borer:
Keep up to date with local emerald ash borer management guidelines and resources in your state.
Colorado
City of Fort Collins, Denver extension, Colorado State Forest Service, Boulder County
Oregon
EAB invasive species alert, emerald ash borer in Oregon, Oregon invasive species council, City of Portland
Montana
Urban IPM EAB website, State of Montana EAB field guide
Utah
Utah State University extension
Wyoming
Management information
Contact a professional in your area
If you suspect a tree on your property is affected, it is crucial to take immediate action. Emerald ash borer is highly destructive and can cause significant damage to ash trees. However, dealing with this pest issue requires specialized knowledge and equipment. Please do not attempt to handle this problem on your own. Instead, contact an ISA certified arborist in your area. These experts are trained to identify, treat, and manage emerald ash borer infestations safely and effectively. Attempting to address the issue without professional help can lead to further damage to your trees and potentially pose safety risks.
Why is it so important to manage an emerald ash borer infestation?
- Tree health and safety: emerald ash borer feeding disrupts the overall health of ash trees and negatively impacts the tree’s ability to transport water and nutrients. This can lead to tree death, which leads to an increased risk of falling branches or entire trees, leading to property damage or personal injury.
- Environmental impact: Ash trees are extensively planted in the Western region, providing shade and important habitat for wildlife. The loss of ash trees can be disruptive to local ecosystems.
- Economic considerations: The cost of removing dead or dying ash trees is significant.
- Preventing spread of emerald ash borer: Managing an infestation helps prevent the spread of emerald ash borer to other areas. Management is vital for protecting other ash trees on neighboring properties and public spaces.
Insecticide information
Before taking any steps to apply insecticides to your ash trees, you should first consult with a professional arborist to assess the health of your ash trees and determine the best treatment plan. A professional will be able to help you identify the most appropriate treatment plan. You want to ensure that, if you decide to use insecticides to treat your trees, your plan is safe and effective.
Dinotefuran and imidacloprid were formerly recommended treatments, but the latest research indicates they are no longer effective against emerald ash borer. Research is ongoing in Colorado to provide more data regarding insecticide efficacy against emerald ash borer. For now, we can glean information from other universities.
A study conducted by Michigan State University evaluated the effectiveness of two insecticides, emamectin benzoate (applied as trunk injections) and imidacloprid (applied as soil drench), in controlling emerald ash borer on green ash trees over three years. Trunk injections of emamectin benzoate were more effective in reducing emerald ash borer larvae and exit holes compared to soil applications of imidacloprid. Another study conducted by Michigan State University examines the effectiveness of different insecticides in controlling emerald ash borer over six years. Researchers treated green ash trees with imidacloprid, dinotefuran, or emamectin benzoate at various intervals. Emamectin benzoate trunk injections were most effective, significantly reducing EAB larvae even three years post-treatment. Dinotefuran trunk sprays also helped, while imidacloprid was less effective.
Where to report findings
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.
Utah
If you suspect EAB in Utah, contact the https://extension.usu.edu/pests/uppdl/index or the Insect and Pest Program at the Utah Department of Agriculture and Food.
For Wyoming and other states, you can submit detection information to USDA-APHIS.
Resources for WIPM outreach and implementation grant collaborators
If you’re part of our EAB outreach and implementation grant team, you can access our shared folder with resources here.
References and helpful links
Need Insect Identification Help?
We offer agricultural insect identification services through our Plant Diagnostic Clinic and laboratory. We now charge a $15 identification fee. Please visit the Plant Clinic for sample submission instructions.