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. Experts agree that it is just a matter of time before it is found in Minnesota. 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.
Slowing the Arrival of EAB & Cooperative Detection Efforts
EAB adults can fly at least 1/2 mile from the tree where they emerge. At this rate it would take decades for EAB to reach Minnesota. The most likely way that EAB will reach us is by people moving ash logs, ash firewood or infested ash trees from nurseries. This is one reason why the MPRB has stopped planting ash trees. The shipments of ash nursery trees and ash logs is now federally regulated and transporting firewood outside of quarantined areas is illegal. Unfortunately, it is the transportation of infested firewood that poses the biggest risk of intoduction. The simplest way to slow the spread of EAB is to not move firewood.
The earlier that EAB is found, the sooner it can be dealt with. The lead agency in Minnesota for preparing for and detecting EAB is the Minnesota Department of Agriculture (MDA). The Minneapolis Park and Recreation Board (MPRB) Forestry Division has been actively cooperating with the MDA in this effort for years. This has entailed participation in the state’s EAB Strategic Planning Team which led to the creation of the EAB Response Plan. Cooperation has also meant the provision of wild grown ash trees that are sacrificed as EAB bait. Such trees are called trap trees and are removed and examined for the presence of EAB.
Experts agree that EAB will eventually be detected in Minnesota. In fact it may already be here but has not yet been found. Once EAB is found, the MDA will implement its EAB Response Plan. A variety of options are laid out in the plan ranging from suppression (limit the spread of EAB in Minnesota) to eradication (remove EAB from Minnesota). The extent of an infestation will determine which course of action will be pursued.
Links
Contact Information
For more information about EAB and how the MPRB takes care of our urban forest call the Forestry Division at 612-370-4900.
