Emerald Ash Borer

Emerald Ash Borer has been discovered in Forest Lake

The emerald ash borer (EAB) is a very destructive wood-boring insect pest of ash trees and in June of 2019, EAB was discovered in an Ash tree at the Forest Hills Golf Course in Forest Lake.  Ash is the only known host of this borer in the United States.  The exotic beetle is native to Asia, including China, Japan, Mongolia, Korea, the Russian Far East and Taiwan.  It was first discovered in North America in southeast Michigan in June 2002, although it was likely introduced at least 10 years earlier.  EAB was first discovered in Minnesota in 2009 and has spread through predominately the SE area of the State. 

What to do if you suspect you have an infected tree?

Map showing EAB Infestations in Minnesota:


What does the emerald ash borer (EAB) look like? 

The emerald ash borer is a small, metallic green beetle about 3/8" to ½" long and 1/16 inch wide that emerges from the inner bark of ash trees from May through September, creating a D-shaped exit hole.  Minnesota Department of Agriculture considers May 1 – September 30 to be the flight season for emerald ash borer (EAB). This means that EAB adult beetles are emerging from infested wood or trees and flying in search of new hosts during this time. EAB larvae complete their development by pupating into adult beetles in the spring and early summer.

The larva of the beetle is the destructive stage of the life cycle, disrupting the movement of nutrients and water uptake in the tree. A full-grown larva averages 1 1/2 inches in length and has a series of bell-shaped body segments.

This beetle attacks only true ash (Fraxinus sp.) including green ash (F. pennsylvanica), white ash (F. Americana), black ash (F. nigra) and blue ash (F. quadrangulata).  Mountain ash (Sorbus sp.) is not a true ash and not susceptible to the borer.


Frequently Asked Questions

Frequently Asked Questions about Emerald Ash Borer (EAB)

Does EAB kill all trees?

No. EAB only attacks true ash trees in the Fraxinus genus such as Green Ash, Black Ash and White Ash, Mountain Ash (genus Sorbus) is not a true ash and is not attacked by EAB.

Is my tree an Ash Tree?

If your tree has compound leaves (a leaf with many leaflets) and branches that grow opposite of each other, you may have an ash tree. This resource from the Minnesota DNR can help you learn how to identify if your tree is an ash tree:


How do I know if my tree is infested by EAB?

If your tree is an ash tree, it is vulnerable to EAB and will likely become infested. The signs of an early EAB infestation can be difficult to see. As the infestation grows (and greater harm is caused to the tree), the signs become more visible.

The Minnesota Department of Agriculture has a step by step process in determining if your tree has EAB.


If you value your ash tree, the best course of action is to protect the tree from infestation instead of waiting to see if it becomes infested.

How does EAB kill ash trees?

EAB larva (immature beetle) eat the inner bark of an ash tree, essentially eating away the tree’s circulatory system for transporting food and water. The inner bark does not grow back. Within 2 to 5 years of infestation the tree dies from lack of food and water. The amount of time it takes for an ash tree to die from an EAB infestation depends on the size of the tree and the size of the infestation.

If an ash tree has EAB, can it be saved?

An EAB-infested ash tree may be saved if the infestation is caught early (within the first couple of years of infestation) and the tree is otherwise healthy. However, once an infested ash tree has lost about 30% or more of its leaf canopy, it has become very compromised and is unlikely to survive even with treatment. Depending on the size and health of an ash tree, it may take anywhere between 2 to 5 years for a tree to die from an EAB infestation.

What can I do to protect my ash trees?

A pesticide treatment is the only reliable way to protect your ash tree from an EAB infestation. And a pesticide treatment may save an otherwise healthy tree with a mild EAB infestation.

For general health, you should also keep your ash tree properly watered and pruned (but avoid pruning during the EAB active season May 2 to September 30).

Who can perform the pesticide treatment?

For private trees, the City-allowed methods include trunk injection (recommended), soil injection, spraying, and soil drenching. However, soil drenching is not allowed for boulevard (right-of-way) trees and is not recommended for private trees because of environmental concerns.

While some pesticides are sold at retail locations, others may only be purchased and applied by a state-licensed commercial pesticide applicator. The Minnesota Department of Agriculture (MDA) recommends that property owners ask to see an applicator’s identification card and verify that the license is current and includes turf and ornamental licensure before allowing any application work on their property. Property owners may also contact the MDA at (651) 201-6615 to verify proper licensing. You can also check the MDA Online Licensing System.


How much does the pesticide treatment cost?

The cost of treatment to protect an ash tree from EAB varies based upon pesticide, application method and tree size. Typical cost can range anywhere from $50 to $200, and some treatments last two years or more.

How can I select a good tree care company?

Avoid door-to-door salesman and stick with reputable, established firms. If you’re hiring a company to treat your ash tree, make sure that they have a valid commercial pesticide applicator license from the Minnesota Department of Agriculture.

Should I be planting or removing ash trees?

Because of the overabundance of ash in urban landscapes and other sites, it is strongly recommended not to plant additional ash. However, if you have an ash in your yard and it is healthy, it is not necessary to remove it. Instead, consider planting a tree adjacent to your existing ash to avoid a drastic loss of shade if and when your ash tree must be removed. The University of Minnesota has a list of recommended trees for Minnesota.


What else can I do to help prevent the spread of EAB?

Adult (beetle) Emerald Ash Borers typically only fly short distances of about one-quarter mile, so the natural spread of the destructive insect is slow. However, humans have helped EAB spread by moving infected firewood and other wood products from an infested site. Do not move firewood—even if you intend to burn it promptly. The insects can escape from the wood quickly and infect new sites. The best prevention is to keep EAB contained