Ash Trees and the Emerald Ash Borer

By John Wilson, Extension Educator

The emerald ash borer has the potential to be devastating to ash trees when it gets to Nebraska. But the key word here is WHEN! Emerald ash borer has not yet been found in Nebraska. The nearest it has been confirmed is in Iowa, about 80 miles east of Plattsmouth, Nebraska.

This borer has been in the news long enough tree owners are asking if they should start treating, or take the more radical step of removing  ash trees. I just had someone in my office this week that wanted to cut down a couple healthy ash trees because of this potential threat. Now I have an ash tree just east of my house and I’m sure someday I may need to remove it if ash borer gets here.

But I’m not going to cut it down now and give up potentially 10 to 15 years of shade and beauty for a pest that might get here someday. And I’m not going to spend money on treatments to treat a pest that is not here.

The recommendation of the Nebraska Forest Service and UNL Extension is to wait to begin treatment until emerald ash borer is confirmed to be within 15 miles of a tree.  According to the Nebraska Forest Service, treating trees beyond 15 miles will likely provide little or no benefit to the tree but will result in unnecessary environmental exposure to pesticides as well as unneeded expenses.

If you have an ash tree, you should know that state and federal agencies are monitoring emerald ash borer infestations and will provide updates when it is found in Nebraska. Information about it and about when and how to treat ash trees can be monitored on the Nebraska Forest Service website. Go to http://nfs.unl.edu.

After I tell people to wait, I’m often asked what if emerald ash borer is in Nebraska but hasn’t yet been found. It can take up to five years for this borer to kill a tree. So once it is confirmed, it has likely been in the state for at least a few years. However, unlike pine wilt killing Scotch pine where the tree must be treated prior to the nematode infesting the tree, ash trees that are already infested with emerald ash borer are still treatable and can be saved if the damage is not too severe.

Instead of making pesticide applications likely to be of little benefit, become more informed to help make decisions about EAB. If you have an ash tree, decide if you are willing to treat the tree on an annual basis or if you will replace the tree.

Valuable trees, such as those providing shade for a home and are in good condition, may be worth the cost of an annual treatment. Trees with health or structural issues or those not planted in key locations, may best be replaced rather than treated annually. For example, if a tree has branch dieback, sparse foliage, or severe trunk injuries, it is probably not worth the expense of treating.

If you are planting a new tree this spring, avoid ash trees. Most types of ash are susceptible to emerald ash borer. If you know you will not treat an ash tree once it is infested, do you have space on your property to plant another tree now to take over the landscape function if the ash tree dies?

When Dutch elm disease killed American Elms, many of these trees were replaced with green ash. This created another monoculture susceptible to pests. We could now lose a large percentage of these trees. Let’s not make the same mistake twice. Select trees for diversity.

A few readily available large trees to plant are honeylocust, American linden, Norway maple, Miyabe maple, hybrid elms and white oak. Other species not frequently planted in a landscape include Kentucky coffeetree, shagbark and bitternut hickory, silver linden and horse chestnut.

For more information on emerald ash borer or on selecting a replacement shade tree, contact your local UNL Extension office.