Emerald Ash Borer -- What To Do?

The emerald ash borer.

Since Emerald Ash Borer (EAB) was first discovered near Detroit in 2001, it has killed tens of millions of ash trees in southeastern Michigan along, with tens of millions more lost in Ohio, Illinois, Indiana, Pennsylvania, West Vriginia, Missouri, Wisconsin, Virginia, Ontario, and Quebec, according to www.emeraldashborerer.info. In round figures, that's at least 40 million dead ash trees in seven years.

In 2008 EAB was found in eastern Wisconsins, causing many professionals to think Minnesota's ash have time before EAB feeds its way across Wisconsin. In 2009 a pocket of EAB infested trees were discovered south of La Crosse. The discovery of an EAB infestation means that dead or soon-to-be dead ash trees were found. Based on the ash tree losses east of Minnesota, the oncoming threat of widespread losses of our native and landscape ash trees looks real. There is time for action.

Planning
Start by making an assessment of the overall condition of all your trees, not just the ash. Tree owners are often in love with a deeply flawed tree that should have been removed long ago. Determine how all the trees on the site interact together. For example, an ash tree might be falling apart, or suppressing the growth of another more valuable tree. What are the goals for the landscape? Many people are averse to removing any trees, no matter the condition or long term health. A significant number of tree owners are equally disinterested in using chemical treatments. And then there is the budget for doing the work. Might it be cheaper to remove in the winter? Could we wait to treat until fall? Should I treat all my ash trees to save them? Or cut them all down because they are all going to die anyway?

Planting
Planting another tree or trees, depending on the specifics of your site and the goals of your landscape might be the best plan. Although there is always time for planing, get going before you lose the time it takes to grow more shade. Plant a variety of tree species to minimize the threat of any one insect or disease threat. I agree with Tom Powers' article in the April Scoop, the autumn blaze maple is a great tree, but planting them only is not the correct response to the EAB problem.

Chemical Controls
There are different chemicals available to treat for EAB. Basal drench, soil injected or trunk injected chemical treatments, not spraying, are the best application methods. By the time the obvious signs of infestations appear it is too late for chemical treatment. If chemical treatments make sense for your valuable ash tree(s) you must start before infestations. Properly applied, applications prior to infestation can be effective. Annual or biannual reapplication is required depending on material used.

Recently I saw a news story about the decline of donations to the arts in Detroit. Many of the interviews were outside and there were very few trees in the background. Regardless of how many trees are treated we will need more trees planted. Most of the shade we sit under was planted by those who came before us.

(Originally published in the June 2009 issue of The Arborist, the magazine of the Minnesota Nursery and Landscape Association. View a printable version.)