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Emerald Ash Borer Discoveries Threaten Le Sueur County

With the confirmation of emerald ash borer (EAB) beetle in St. Clair, Le Sueur County is now surrounded by this damaging pest. Now, is the time to decide what to do with your ash trees.

What makes EAB so devastating is how effective it is in killing its host. I see many sick trees in my line of work, but few pests can kill a healthy tree just by itself. EAB mortality rate for native ash is just under 100%. It may take a few years, but no matter how giant your ash is now, it will die if exposed to EAB. In Asia, where the beetle comes from, the trees there have tricks up their bark to fend off these pests. While these resistance traits could perhaps be bred into North American ashes, it takes many years to do this with trees. American elm for example, was decimated by Dutch elm disease, which was introduced in the 1920’s. It took decades for plant breeders to produce resistant hybrids for the public. Ironically, these elm hybrids are now recommended to replace the ash tree, as ash trees were once used to replace the elm tree years ago.

What should you do now? First, scout your property for ash trees. The location of the ash tree is important. If ash trees are in a woodland and will not damage anything if they fall, they could be left for wildlife habitat. 

Otherwise, if there is risk to people or property, the ash should be treated or removed. EAB does not care about your shed or roof when it leaves a weakened tree behind. Action should be taken for these hazard trees—even if the ash is healthy. One reason to remove ash trees before they get sick from EAB is cost. A dead tree is more expensive to remove than a living one. Another reason is to avoid the rush when the infestation becomes severe in your area, as tree experts will be busy.

If you decide to save some of your ash trees, there are effective products available to prevent (but not reverse) damage. Depending on the tree’s diameter 4 ½ feet up, you can treat the tree yourself. Trees greater than a 20-inch diameter will require certified arborists. Price estimates usually range from $8-10 dollars per inch. Certain treatments might be applied yearly, while others every two years. Be sure to read and follow the label if you apply any treatment yourself.

If you need to remove your ash trees, hire certified tree care professionals. Try and get at least two estimates, ask for referrals, and see proof of insurance. You can check their certification at the International Society of Arboriculture’s website, www.treesaregood.org/.

For more information about emerald ash borer, I encourage folks to visit the Minnesota Department of Agriculture’s webpage at www.mda.state.mn.us/eab. Other great resources include Purdue Extension’s EAB Cost Calculator https://int.entm.purdue.edu/ext/treecomputer/. As always, you are welcome to contact us at the UMN Extension office as well.

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