Jonathan Heaton is an ISA certified arborist working for Bartlett Tree Experts in St. Paul Minnesota. He can be reached at or on twitter @mnarborist.

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A Battle with Emerald Ash Borer is in Your Future
by Jonathan Heaton       #Advice   #Feature   #Insects   #Invasives

Close-up view of adult emerald ash borer. 1

Emerald ash borer (Agrilus planipennis) is an invasive beetle that has killed tens of millions of ash trees in the Midwest since first discovered in Michigan in 2002. If you haven’t already dealt with this serious problem, you, your neighborhood and community will face it in the not-too-distant future.

No species of ash (Fraxinus) is immune from attack by this Asian import that does not have any natural predators in this country. It’s just a matter of time for most of us, as the insect spreads far and wide.

Although a complicated issue, you can help by understanding a few things about emerald ash borer (frequently called EAB), how it works and options for management.

It is frequently incorrectly reported that nothing can be done to save ash trees, which account for 10 to 40 percent of urban trees in the Midwest. Fortunately, there are options for saving important trees and managing the impact and spread of EAB.

Identify Ash Trees

The first step to managing EAB is learning to identify ash trees. They have unique bark, leaves and branching habits. I think the best way to learn how to identify a tree is to ask another person with experience to show you, or visit an arboretum, public park or other place that has trees labeled. Online resources ( and guidebooks are good, but a picture is no substitute for a live tree.

Adult EAB beetles lay eggs on the bark of ash trees. The larvae tunnel into the tree and eat the portion of the wood responsible for transporting water, nutrients and sugars through the tree. Each year the larvae grow into adult beetles, which emerge from the tree and lay more eggs, increasing the population exponentially. In as little as three years, the damage becomes severe enough to kill the tree.

Infested trees begin dying at the top and will usually grow numerous sprouts from the lower trunk. When the adult beetles emerge, they leave a characteristic D-shaped hole, about the size of a pencil eraser, in the bark. Many inspectors find that the easiest way to spot infested trees is to look for extensive, irregular missing patches of bark caused by woodpeckers feeding on the larvae. There are other problems that can cause similar symptoms, so, if you have an ash tree that you suspect is infested, contact a certified arborist.

Missing patches of bark caused by woodpeckers feeding on EAB larvae. 2

Infested trees die from the top down. They will often grow thick water sprouts from the trunk. 3

Management Options

You may or may not have ash trees on your property. Either way, you’ll want to know about options for management. Your community likely has a fair number of ash trees, which like most trees, have a significant impact on the quality and character of your neighborhood, such as shading sidewalks, storm water absorption and helping clean the air.

In my opinion, far too many municipalities have taken an approach heavily weighted toward removal, based on the misconception that nothing else can be done. The only way to change this is if informed and involved citizens fight to save trees where it makes sense.

Options for managing ash trees include:

•  Preemptive removal and possibly replacement trees

•  Removing infested trees as they become hazardous

•  Insecticide treatments to protect trees

•  Efforts to slow and limit the spread, including quarantines and biological control

If you have ash trees on your property, you will need to weigh the cost of removal against the cost of treatment with the benefits they provide. Take into consideration the size and condition of the tree. A small tree is easy to replace. Trees that are in poor health or too close to other trees or structures may need to be removed anyway and are not worth treating. In some cases, the ash tree may not be important enough to warrant treatment. (If the decision is to remove problematic trees, do so before they are infested. Infested or dead trees are weaker, which makes them more difficult and expensive to remove.)

If you decide to keep the tree, insecticide treatments need to be done before it is infested. A good guideline is to begin treatments when an EAB infestation is within 15 miles of your tree.

Insecticide and Applications

There is a wide range of opinions regarding products and application methods for protecting ash. Several universities are conducting research to learn more about the best methods, so current recommendations may change. At this point, research is showing the best control with a product called Tree-age, especially for trees with a diameter greater than 20 inches. This needs to be applied by a licensed, certified applicator every other year. The disadvantage of Tree-age is that it requires drilling holes into the trunk to inject the product, which is why it is important to hire a professional applicator with a good reputation. It is important that Tree-age is injected correctly, so that it is effective and to minimize damage from drilling.

For trees under 20-inch diameter, products containing imidacloprid (brand names include Bayer Advance and Optrol) can be poured around the trunk in a soil drench. This has been reasonably effective. Imidacloprid tends to stick to organic matter such as mulch, so it is important to dig a small trench down to bare soil around the trunk. Water the tree well for one to two weeks after you apply the chemical to help the tree absorb it through the roots. Many commercial applicators will use a soil probe with a pump to inject the product beneath the surface so that they don’t need to dig a trench. Watering is just as important, even if you hire someone to do the soil treatment for you. Soil treatments need to be done every year.

There are several efforts on a local and national level to help monitor and slow the spread of EAB. 

  • You may have seen purple boxes hanging in trees. These are traps that help arborists and researchers know where EAB has spread, but they do not directly limit the population. There are some new programs that we hope will help to limit the spread.
  • A pilot program in Minnesota is using dogs to sniff out wood that is infested with EAB. This can help to find wood that needs to be disposed of in a way that kills the larvae. 
  • Researchers have found wasps from EAB’s natural habitat in Asia that parasitize EAB larvae. They are currently testing the wasps to see how far they fly and if they can survive in cold climates. Results are promising. 
  • Many people have participated in ash identification programs, such as Neighbors Against Bad Bugs in Indiana. Citizens tag public ash trees and raise awareness of the impact that the loss of these will have. In some cases, the tags list the annual benefits in dollars each tree provides to further encourage saving trees. Some have joined with their neighbors to cover the cost of treating public trees if the government will agree not to cut them down.

Organize to Fight EAB

Don’t Do Battle Alone

Take Advantage of These Helpful Resources:

•    To find a certified arborist, visit the International Society of Arboriculture’s website,

• is a cooperative venture including Michigan, Connecticut, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Massachusetts, Minnesota, Missouri, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, Wisconsin, Ontario and Quebec to share the latest information about emerald ash borer. 

•  University of Minnesota,

•  Iowa State University,

•  University of Wisconsin,

•  State of Michigan,

You can get involved in several ways to help combat EAB on a larger level. First and foremost, you should not move any firewood and you should discourage others. People moving firewood is the prime way EAB has spread so quickly throughout the Midwest and Eastern United States, the two most heavily infested regions. Always obey quarantines.

Become involved with your local government to help shape the way officials handle ash trees along streets, parks and other public spaces. You can get involved by attending city meetings and contacting public officials to advocate saving healthy trees instead of wholesale removal.

Many cities have essentially given up when faced with an EAB infestation. The perception seems to be that treatments are not effective or are too expensive, making removal the only option. It doesn’t help that many federal grants only cover removal or replacement.    

Treatments are reasonably effective and not expensive, especially when the monetary benefits of mature street trees are taken into account. For example, a single mature tree can capture several hundred gallons of storm water in a year, reducing the strain on municipal sewer systems and the need for expensive upgrades.

In my opinion a balanced approach, with a complete understanding of the benefits of trees, needs to be taken. Trees under 10 to 15 inches in diameter, or with structural defects and declining health should be removed and replaced. Larger trees in good condition should be treated wherever it is practical.

While emerald ash borer may seem like a staggering or insurmountable problem, it is possible to fight. Our experiences with EAB will also help us gain valuable knowledge for other invasive pests that will inevitably threaten our forests in the future. With education, involvement and a balanced approach, many ash trees can be saved and the spread of this devastating pest can be reduced.


1. Photo courtesy of Pennsylvania Department of Conservation and Natural Resources - Forestry Archive,
2. Photo courtesy of Jim Tresouthick, Village of Homewood,
3. Photo courtesy of Daniel Herms, The Ohio State University,

From State-by-State Gardening March/April 2013.


Posted: 03/24/14   RSS | Print


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