Emerald Ash Borer

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Many invasive species have a long history in the place that they infect. However, the Emerald Ash Borer is a relatively new pest for Wisconsin. They were accidentally introduced around 2002. Since then, they have created serious damage in Wisconsin forests. This article will cover what the Emerald Ash Borer is, where they came from, how they came to Wisconsin, other places they have infected, symptoms, why we need to get rid of them, and how to get rid of them.

What is the Emerald Ash Borer?

Emerald Ash Borer (Agrilus planipennis) is an invasive, wood boring beetle. It eats the tissue underneath the bark of ash trees, thus killing the tree in about two years. The beetle is native to East Asia and was brought to the United States by accident. The beetles hitched a ride in some wooden shipping crates that were shipped from China.

The Emerald Ash Borer is not a threat to human health but it kills our native ash trees of any size, any age, healthy or unhealthy, (according to research by Michigan State University and the US Forest Service).

The larva begins its life inside the ash trees. There it feeds on the inner bark where we can’t see it. The beetle’s consumption of the inner bark interrupts the tree’s ability to move water and other nutrients between the rest of the tree and its roots. Without this constant flow of water and nutrients, the tree eventually starves and dies. This will take between 2-4 years after infestation. There is an estimated 50 million ash trees that are dead or dying because of this beetle. Wisconsin forests are home to more than 770 million ash trees, which is nearly 7% of the tree population. In more urban areas, it’s estimated that, on average, 20% percent of trees are ash.

The beetle can only fly a few miles on its own. But with our accidental help, we have been spreading them by moving firewood, ash trees from nurseries, and other ash products, thus accidentally spreading the pest. [1]

Interview with Mike Grisar

I conducted an email interview with Principal Environmental Consultant, Mike Grisar, from We Energies.

Why Are They an Issue?

"The emerald ash borer is an invasive insect, native to Asia, and is resulting in numerous impacts. Emerald ash borer was first discovered in the US in 2002 near Detroit, MI. It has quickly spread and now is impacting forests and urban tree populations in all but a half dozen states east of the Mississippi River. In Wisconsin, the emerald ash borer was first discovered in 2008 and has quickly spread throughout the entire southern half of Wisconsin as well as a couple of counties in northern Wisconsin. The main reason this is such an issue is that it attacks and quickly kills ash trees. Ash trees comprise nearly 10% of all the trees in Wisconsin; there are approximately three quarters of a million ash trees throughout Wisconsin. Some estimates predict that the vast majority (>98%) of ash trees will succumb to the effects of the Emerald ash borer. In healthy forests, this can happen over a brief, six-year time frame once the ash borer infests an area. The overall result will be that a bit less than 10% of Wisconsin forests will essentially die in a relatively short time frame. Additionally, in urban settings, it’s estimated that ash trees comprise 20% of all street and landscaping. If you picture the impacts, 20% of all urban tree canopy will be wiped out. Drastic economic impacts, perhaps in the 100's of millions if not billions of dollars, are already being realized. It’s affecting home owners, businesses, municipalities, and a host of industries including forestry, utilities, recreation, nursery, chemical production (insecticides), furniture, construction, etc. The bottom line is this one of the most rapid invasions with some of the most devastating and wide reaching impacts by an invasive species that has been observed to date. Ash wood is (which will be ‘was’ in the future) one of two primary sources of wood for Louisville Slugger. The ash borer is even having an impact on MLB. While I don’t subscribe to most theories and scares about global warming or climate change, one of the main topics you often hear with this is the ability for our forests to capture CO2 from the atmosphere. I don’t claim to understand the complex atmospheric dynamics that occur, but wonder if EAB is having some impact with respect to this issue if you think about the fact that 10% of our tree canopy in WI alone will no longer be there to utilize the atmospheric CO2. There is one additional impact that I often think about and have personally seen in just this brief seven year time frame that EAB has been in WI. When the forest canopy opens and creates a sunnier condition on the forest floor, it is a ‘disturbance’ that results to what would have been a more stable, shaded forest setting. When these types of disturbances occur, other species take advantage of the disturbance. One of the top causes of many vegetative invasions by non-native species in forests is disturbance. These can be tree cutting, wind blows, sediment deposition from construction or agricultural run-off, or flooding among others. Disturbance such as increased light penetration from dying trees, gives an opportunity for invasive species such as buckthorn, honeysuckle, reed canary grass, and many others to use their aggressive advantages to invade an area that was otherwise free of these invasive species. This is a long winded explanation to say that dying ash trees from ash borer impacts is resulting in the spread of vegetative invasive species causing a reduction in biodiversity and overall reduction in the quality of forestlands."[2]

Can They be Prevented?

"In short, they can no longer be prevented from spreading. The focus and goal now for most management efforts is minimizing how fast they spread. In a natural setting, the ash borer can disperse less than 1 mile annually, which frankly is a very short distance. However, when humans move wood, they move ash and the ash borer. The primary culprit of this is hauling firewood from an invaded forest source to another location (a home, vacation cabin, or campground). Second, or maybe equal to that, is shipping crates and other wood products used for transporting goods across the state, the country, and even the globe. In fact, this is how it first came to Newburg, WI in 2008; it was through wood shipping pallets." [3]

Do You Think They Could be Permanently Exterminated?

"It will never be exterminated. Unfortunately, it is here to stay. The only way to get rid of it in North America is to kill every ash tree across the continent. This, obviously, is not a reasonable outcome to try to achieve." [4]

Other Places That Have Been Infected

The Emerald Ash Borer was thought to occur in six counties in southeastern Michigan: Livingston, Macomb, Monroe, Oakland, Washtenaw and Wayne, and in Essex County Ontario. Since then, the technology for finding an Emerald Ash Borer infestation has improved. Now it’s found in Michigan, Arkansas, Colorado, Connecticut, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Minnesota, Missouri, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, Wisconsin, Ontario and Quebec. With it not only invading America, but Canada as well, the Emerald Ash Borer has become an international problem. It’s important to keep an eye out for symptoms to make sure any infected areas can be quarantined. The infections are mostly been spread through transporting firewood. When purchasing firewood, make sure to not transport them far away from the site of purchase in case your firewood has been infected. [5]

Symptoms of an Infestation

Like any living thing with a disease or sickness, trees will show symptoms of an infestation. The six main symptoms the tress will show are as follows:

  • D-shaped holes in the bark, where the larvae exit the inner tree
  • S-shaped tunnels on surface under the bark
  • Sprout growth at the base of the tree
  • Seeing more woodpecker activity than normal
  • Death of the tree starting at the top
  • Vertical splits in the bark of the tree



  1. "Emerald Ash Borer: Frequently Asked Questions," Dr. Deborah McCullough and Robin Usborne, Michigan State University, February 2015.
  2. Mike Grisar, Principal Environmental Consultant from We Energies, email interview, Dec 9
  3. Mike Grisar, Principal Environmental Consultant from We Energies, email interview, Dec 9
  4. Mike Grisar, Principal Environmental Consultant from We Energies, email interview, Dec 9
  5. "Emerald Ash Borer: Frequently Asked Questions," Dr. Deborah McCullough and Robin Usborne, Michigan State University, February 2015.
  6. "What is that Purple Thing Hanging in the Tree?," Thomas Worthley, UCONN Cooperative Extension, 2011.

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