Emerald Ash Borer

Emerald Ash Borer (EAB) was discovered in Tower Hill Park in the Prospect Park East River Road neighborhood of southeast Minneapolis in March 2010. This was the first officially identified infestation in Minneapolis and is within a mile of the first identified infestation in St. Paul in 2009.

As a result, the MPRB’s Forestry Department has fully activated its EAB Preparedness Plan, which seeks to minimize the environmental, economic and aesthetic impact on the city’s urban forest. Proactive measures include removal of the infested trees, establishment of trap trees, continued surveying of ash trees both in the area and city-wide and continued removal of ash trees that are damaged and defective.

The lead agency in Minnesota in the EAB battle is the Minnesota Department of Agriculture (MDA). The MPRB Forestry Department has been actively cooperating with the MDA in this effort for years and will continue to do so.

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History & Potential Impact
The Emerald Ash Borer (EAB) is an invasive pest introduced from Asia that attacks ash trees (Fraxinus spp.). This metallic wood boring beetle was first found in Detroit, MI, and Ontario, Canada, in 2002. It is believed to have arrived in shipping crates. Since the initial discovery it has been identified in Ohio, Pennsylvania, Indiana, Illinois, Maryland and West Virginia.

The destructive potential of EAB is enormous because there is currently no known cure. It has already killed more than 40 million ash trees nationwide, most of which were in southeast Michigan. Minnesota has the potential to lose 867 million trees because it has one of the highest volumes of forestland ash in the U.S.

As bad as these losses would be, they do not address the losses that would be suffered by municipalities. In Minneapolis the impact to the total urban forest canopy would be significant because 21 percent of all trees, both public and private, are ash. This translates into more than 200,000 trees.

On public property, Minneapolis would lose approximately 38,000 ash trees growing on boulevards. The cost of removal, stump grinding and replanting of these trees would exceed $26 million. This does not include the tens of thousands of ash trees growing in parks and natural areas such as along the Mississippi River corridor.

How EAB Kills Ash Trees
EAB kills trees over a period of one to four years depending on the size of the tree. It is the larval stage that does the damage. The larvae live under the bark of the tree and feed in the tissue layer directly beneath the bark. This layer contains the vascular system of the tree which transports water from the roots to the crown. As the larvae develop they create tunnels throughout this tissue. This activity kills the tree by stopping the flow of water and nutrients.

The most prominent symptom of EAB is dieback of the tree canopy. It is not unusual for as many as one half of a tree’s branches to die back during the first year of attack. The tree tries to compensate for this loss by sprouting new growth below the level of infestation. At this time the bark may begin to split. Eventually the adult beetles emerge from the bark. In the process of emerging as adults, they leave a “D” shaped exit hole that is about 1/8 inch wide.

EAB adults can fly at least 1/2 mile a year from the tree where they emerge. The most likely way that EAB spreads is by people moving ash logs, ash firewood or infested ash trees from nurseries. The simplest way to slow the spread of EAB is to not move firewood.

The shipping of ash nursery trees and ash logs is now federally regulated and transporting firewood outside of quarantined areas is illegal. Due to the local discovery of the infestation, Ramsey and Hennepin counties have been placed under quarantine.

Contact Information
For more information about EAB and how the MPRB takes care of our urban forest call the Forestry Department at 612-313-7710 or e-mail forestry@minneapolisparks.org.