"Has Emerald Ash Borer Infested My Ash Trees?"
Quick & Easy Leaf Identification Helps to Prevent, Treat EAB Damage
Oct 12, 2009
Many homeowners in the US and Canada may have heard about the devastating infestation of Emerald Ash Borer (EAB), an invasive Asian beetle accidentally introduced around the year 2000. EAB feeds on the vascular systems of ash trees while in its larval stage, which causes the trees to suffer thinning canopies and ultimate defoliation. Treatments are available to help strengthen the trees' defense against this pest, but one must identify where the problem is before it can be addressed.
Identifying Ash Tree Leaves
Perhaps the easiest way for a homeowner to identify an ash tree is by looking at its leaves. Though there are some subtle variances among the different species of ash, all ashes have opposite branching compound leaves. A compound leaf is one that is made up of more than one distinct leaflet. A maple leaf, for example, has only one distinct leaflet and so is simple, not compound. Most ash leaves have 5-9 leaflets that branch in pairs on opposite sides of the stem (except for the single terminal leaflet). Unfortunately, some other tree species have similar leaves and distinguishing one from the other can be a bit tricky.
Distinguishing Ash From Walnut, Hickory, and Box Elder
The black walnut, like the ash, has opposite branching compound leaves; but, unlike the ash, it has 12-14 leaflets. Hickory leaves are also opposite and compound, but the size of the leaves differs from the ash. On an ash leaf, the largest leaflets occur near the middle of the branch, whereas on a hickory leaf the largest leaflets occur at the terminal end. The leaves of a box elder can look like some species of ash from a distance, as some (e.g. Blue Ash) display toothed leaves (leaves with sharp-edged protrusions), but up close one can see that box elder leaves are lobed, or have soft-edged protrusions. These distinctions are somewhat subtle, and some may find it easiest to make them using a pair of binoculars or by studying fallen leaves.
Identifying and Treating EAB Damage
Once the homeowner has identified which of her trees are ash, she can determine the extent of Emerald Ash Borer damage. This is best done in the early summer (June) after the trees' canopies have had a chance to fill out but before they begin to change color and fall. If a tree has been significantly affected by the feeding of EAB larvae, it will lose the ability to grow leaves as well as it should, leading first to small, unhealthy-looking leaves and then ultimately to bare branches. This process of defoliation occurs at the top (or crown) of the tree first and works its way down.
The homeowner should stand some distance away from the tree so she can view it in its entirety. She should then note whether there are bare branches in the crown of the tree, if the leaves are smaller than they once were, and generally if the canopy looks as full as it should. If it appears that about 50% of the canopy is missing, that tree will likely be dead within two to three years. But, if there appears to be only 0-35% canopy loss, the homeowner might be interested in the treatment options for her tree. Healthy-looking ash trees are still at risk of EAB infestation and can be protected by a number of pesticide treatments, but the homeowner must be certain it's an ash tree she's treating!
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