What to do about Emerald Ash Borer (EAB)?
Emerald Ash Borer (EAB) has become a household name and a dreaded pest. Most people have heard of the devastation this pest has wrought on Ash trees in the eastern United States and know that it has an undeniable presence in the Minneapolis and St. Paul areas now. This pest indiscriminately kills Ash (genus Fraxinus) regardless of the tree’s vigor or size. Emerald Ash Borer larvae (youth life stage) create meandering tunnels under the bark which disrupts the flow of nutrients and water between the leaves and roots, eventually this kills the tree. For more details on this pest, life cycle and current location in Minnesota please see Minnesota Department of Agriculture’s EAB information website. Now that this pest is in our backyard, it is time to finalize the strategy to use regarding this issue of EAB.
A Black Ash (Fraxinus nigra) in decline as a result of EAB, found Spring 2018 in Woodbury, MN by Horticulture Services | Photo By B.J. Holty
When considered simply, there are a three basic strategies for dealing with EAB: remove trees before infestation, remove trees after infestation, or treat to prevent infestation.
1. The first strategy, remove trees before infestation, is most suitable if trees are young, less than 10” diameter, as it is less expensive to remove a small tree than a large one. Young Ash grow quickly and will cost substantially more to remove each year removal is delayed. Also, if a small Ash is being removed and replaced with a 2”-3” diameter shade tree the impact on the landscape is much less alarming than replacing a large Ash with the same 2”-3” tree. Remove the young Ash, replace with an Ash alternative and move on. (See list of alternatives appropriate for the Twin Cities area below.)
2. The second strategy, remove trees after infestation, is suitable for mature Ash which are not growing rapidly and are not highly valuable. Large Ash are very costly to remove and if the tree is not growing rapidly, these costs can be delayed by removing at a future date, or removing a few trees each year. It can take a few years for EAB to kill a large, mature, otherwise healthy Ash, so there is not a high degree of urgency to remove the tree immediately once it becomes infested. As large limbs begin to die the tree should be removed to avoid risk of these dead limbs falling and causing injury or damage. Cut them down as you can or must and let go of the Ash you’re losing.
3. The third strategy, treat trees to prevent infestation, is appropriate for middle-aged to mature, healthy, valuable Ash. A middle aged Ash can be considered any Ash greater than 10” diameter. A mature Ash is regularly 2’-3’ diameter; the current White Ash champion is 5.8’ diameter. A healthy Ash is one free of harmful pests, pathogens (such as Heart Rot) , and symptoms of stress. A valuable Ash is a well-branched tree performing a critical function in the landscape, such as shading a home or park, blocking an unsightly view, or providing a large structural element in the landscape design. For these middle-aged to mature, healthy, valuable Ash chemical treatment has proven to prevent damage and reverse effects of current infestations of EAB. Some of these treatments need only be applied every 2-3 years and are trunk injected, greatly reducing chemical contact on people and structures. This treatment would likely be necessary to some degree for the remainder of the tree’s lifetime. If the EAB population decreases the treatments could be less frequent.
The three strategies for addressing Emerald Ash Borer will vary depending on your specific population of Ash; you may find a combination of all three methods fits your budget and Ash inventory best.
Following is a Decision Tier to assist you in developing a strategy for dealing with this sure and certain issue of Emerald Ash Borer. Ask yourself these questions as a starting point for your plan.
Click the icon below to view Ash alternatives for the Twin Cities:
The following are links to trees cited in the “Ash Alternative” Table:
Catherine Nickelson | Horticulturist | B.S. Horticulture, University of Minnesota | ISA Certified Arborist