Figure 1: Photo of an adult emerald ash borer that is resting on a chewed leaf

Figure 1: Emerald ash borer, Agrilus planipennis. Photo by D. Miller, USFS,

This fact sheet provides information on emerald ash borer biology and damage symptoms, what you can do right now, management recommendations if the EAB is found in Montana, other ash pests or non-EAB ash issues, and EAB look-alike insects in Montana.

A PDF version of this fact sheet can be found at the bottom of the page.


  1. Emerald ash borer Agrilus planipennis
  2. What’s at Risk in Montana?
  3. Trees at Risk
  4. Detection
  5. Damage
  6. EAB Life Cycle
  7. Common Issues in Montana Ash Trees Not Caused by emerald ash borer
  8. Prevention and Mitigation
  9. Other Ash Pests
  10. EAB Look-Alikes
  11. Symptoms of EAB Infestation
  12. What To Do if You Suspect Emerald Ash Borer
  13. Treatment
  14. Further Information
Figure 2: Photo of a large ash tree that is thick with leaves

Figure 2: Green ash tree. Photo by J. O’Brien, USFS,

Emerald Ash Borer, Agrilus planipennis

The emerald ash borer (EAB) is a destructive wood-boring insect that has killed millions of ash trees in North America. It was first discovered in Detroit, Michigan in 2002, and it likely came from wood packaging material imported from Asia. It has become widely established in 35 states and five Canadian provinces. As of April 2021, it has not been detected in Montana. Unfortunately, it is easily transported on firewood, so Montana is always just one visitor’s mistake away from EAB establishing here.

What’s at Risk in Montana?

Ash are the most commonly planted trees in many Montana communities east of the Continental Divide. Ash species represent more than 40% of all publicly-owned trees in 20 Montana communities. The pest is also easily transported through infested firewood. Emerald ash borer can also naturally spread by flying approximately 2 to 12 miles per year. Ash trees that are killed by EAB become particularly brittle and liable to breakage, which then threatens property and public safety.

Trees at Risk

Emerald ash borer attacks all true ash species (Fraxinus sp.) and the white fringetree, Chionanthus virginicus. Mountain-ash trees are not true ash trees and they cannot become infested with EAB. Proper identification of true ash trees is critical. Ash trees have opposite, compound leaves with short-stalked leaflets. Leaflet margins may be smooth or toothed.


Figure 3: Photo of a cutting of ash leaves, showing leaf structure

Figure 3: Green ash leaves. Photo by P. Wray, ISU,

Detection is difficult, so study the symptoms and be alert. The upper canopy of trees is attacked first, making it difficult to notice early stages of an infestation. Other factors can mimic symptoms of EAB. Ash trees in Montana may show evidence of decline and dieback for a variety of factors, none of which has yet been linked to EAB. The pest is often in the tree for up to four years before symptoms are visible. Green and purple prism traps are not yet proven effective for early detection nor mitigation of emerald ash borer.


The juvenile stage (larva) damages by feeding in the phloem and cambium, which interferes with the tree’s ability to transport nutrients and water. Ultimately, the branch and the trunk are girdled, causing dieback, canopy loss, and death of the tree. Infested trees will usually die within two to four years if left untreated.

Prevention and Mitigation

  • Diversify tree species in the community in both new plantings and regular replacement trees.
  • Remove unhealthy trees.
  • Don't bring out-of-state firewood into Montana.

Visual Guides

Select a title below to expand the page to reveal related images and information.

Step 1: Eggs

  • Eggs laid on outer bark and fissures on trunk and larger branches, mid-June to August
  • Eggs hatch in 14 days
Step 1: Photo of a freshly laid, white-colored, EAB egg, next to an older brown egg

Step 2: Larvae

  • Larvae enter the bark and feed on phloem
  • Overwinter as larvae in outer sapwood or outer bark
Step 2: Picture of an EAB larva, showing a cream color and several bell-shaped segments
Step 4: Photo of an emerald ash borer adult with wings spread, revealing a purplish abdomen

Step 4: Adults

  • Adults emerge late May through June t mate
  • Adults live 3 to 6 weeks
Step 3: Photo of a worm-like EAB pupa nested within some ash wood

Step 3: Pupae

  • Pupate during April and May

EAB Adult

Figure 8: Photo of an shiny insect with no obvious body or color segments, wings folded under matching elytras
  • Metallic green
  • Half an inch long (12mm)
  • Slender, bullet-shaped

EAB Larva

Figure 9: Photo of an emerald ash borer showing an off-white long body with many segments
  • Flat-headed borer
  • Up to 1.5 inches long (38mm)
  • Bell-shaped abdominal segments


EAB life cycle photos provided by Individual authors include: Step 1 D. Miller, Step 2 D. Cappaert, Step 3 D. Cappaert, Step 4 D. Cappaert, Figure 8 Pennsylvania DCNR Forestry, Figure 9 V. Ferreira.

Figure 10: Photo of a large ash tree that has had all of its branches trimmed back

Photo: Montana DNRC

Topped ash trees.

Figure 11: Photo showing several trees with clusters of dead branches

Photo: Montana DNRC

Dieback of ash trees (environmental).

Figure 12: Photo of an ash trunk showing large gashes and scars

Photo: J. O'Bien, USFS

Physical damage from mowers, cars, etc.

Figure 13: Photo of a large ash branch that has fallen on a sidewalk

Photo: S. McConnell

Sudden branch drop.

Ash trees in Montana are commonly stressed by various pests and conditions including lilac/ash borer, western ash bark beetle, cankers/disease, drought, frost, herbicides, and mechanical damage. Homeowners can usually rule out these common issues prior to submitting samples.

Figure 14: Photo of a tree trunk with bark that is flaking off

Photo: S. Katovich,

Damage from lilac/ash borer.

Figure 15: Photo showing shothole-size holes in the trunk of a tree

Photo: W. Cranshaw,

Damage from Western ash bark beetle.

Figure 16: Photo showing deformed clumps of buds on an ash branch

Photo: A. Munson, USFS,

Ash flower gall mite.

Figure 17: Photo of an ash branch showing small scales that resemble oysters

Photo: J. Davidson, Univ. Md,

Oystershell scale.

Figure 18: Photo of an adult Buprestis confluenta, showing green and yellow metallic colors

Photo: V. Ferriera

Buprestis confluenta.

Figure 19: Photo of an adult Chrysobothris sexsignata beetle, showing a gray, purple color

Photo: V. Ferriera

Chrysobothris sexsignata.

Figure 20: Photo of an adult Chrysophana placida showing green and red coloring

Photo: J. Moore

Chrysophana placida.

Figure 21: Photo of an adult tiger beetle showing green coloring

Photo: Pennsylvania DCNR Forestry,

Cicindela decemnotata.

The photos below show common signs of an emerald ash borer infestation.

Figure 22: Photo of an ash tree that is missing bark on large sections of its trunk


Damage from woodpeckers feeding on EAB larvae.

Figure 23: Photo of ash trees that are missing large sections of leaves

Photo: E. Day, Virginia Polytechnic Institute and State University

Thinning in upper canopy.

Figure 24: Photo showing earthworm-sized holes in an ash tree branch

Photo: D. Herms, OSU,

D-shaped exit holes in trunk.

Figure 25: Photo showing a branch with a large split in its bark

Photo: Michigan Dept. of Agriculture

Bark splitting from EAB infestation.

Figure 26: Photo showing earthworm-sized galleries in a tree trunk, resembling squiggly lines

Photo: T. Kimoto, Canadian/Food Inspection Agency,

Serpentine galleries under the bark.

Figure 27: Photo showing many small shoots coming out of the base of a tree

Photo: Pennsylvania DCNR Forestry

Epicormic branches and shoots at base of tree.

What to Do if You Suspect Emerald Ash Borer

If your ash tree exhibits dieback, refer to all possible biotic and abiotic issues in this guide.

For further help, contact a certified arborist in your area. 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.


  • It is unnecessary to do preventive chemical treatments until EAB is confirmed within 30 miles.
  • Work with a certified arborist if infestation is suspected. Remove confirmed infested trees promptly.
  • Chemical treatments can be effective when properly applied (see table).

Application Table

This table consists of 4 columns, row 1 contains headings. Each row of cells describes an active ingredient, its application method, the required applicator type, and the expected period of control.  This table is meant only as a quick-reference, and it should not be a substitute for label directions.

Active Ingredient
Application Method
Applicator Type
Emamectin benzoate
Licensed professional only
2-3 years; 99% reduction in adults
Soil injection or drench
Licensed professional and homeowner
1-yr control; 58-80% mortality of adults and 57-68% reduction in larval densities
Soil injection or drench, trunk spray
Licensed professional and homeowner
1-yr-control; 58-80% mortality of adults and 57-68% reduction in larval densities
Trunk injection
Licensed professional and homeowner
1-2 years; affects EAB reproduction and development of young larvae
Pyrethroids (permethrin, beta-cyfluthrin, bifenthrin)
Trunk, branch, foliage spray (preventive)
Licensed professional only
1-2 years; affects EAB reproduction and development of young larvae

Further Information

Simple graphic depicting a pair of trees

To learn more about emerald ash borers, contact MSU Extension specialist Dr. Lauren Kerzicnik.  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.

The Emerald Ash Borer guide is also available as a printable folded-pamphlet PDF (2MB), and as a standard format PDF (2.1MB)

Photos provided by

The Emerald Ash Borer Fact Sheet was created with support from Montana State University Extension Integrated Pest Management, the Montana Department of Natural Resources and Conservation, the Montana Invasive Species Council, the United States Department of Agriculture, the Don't Move Firewood initiative, and the Montana Urban Community Forestry Association.


Logo: Montana DNRC text over a mountain scene
Logo: USDA text over rolling fields
Logo: MISC text under a fish, insects, and plants
Logo: Don't Move Firewood stylized text resembling logs
Logo: MUCFA text under a house and tree
Logo: MSU Extension IPM stylized text


These recommendations are provided only as a guide.  It is always the pesticide applicator’s responsibility, by law, to read and follow all current label directions for the specific pesticide being used.  Due to constantly changing labels and product registration, recommendations are not meant to replace those provided on the label.  Always consult the product label prior to application.

Common chemical and trade names are used in this publication for clarity. Inclusion of a common chemical or trade name does not imply endorsement of that particular product or brand of herbicide.


Back to Top