Season After Season: The Corona Blog

Emerald Ash Borer – Worst Invasive Tree Pest of this Generation?

Posted by Dr. David Coyle on Fri, Feb, 15, 2019 @ 13:02 PM

Despite bone chilling temperatures this winter, courtesy of the Polar Vortex, you would think that would be enough to wipe out one of the most invasive tree pests, the Emerald Ash Borer, a.k.a, EAB. But you'd be wrong. This single insect has been the demise of millions of North American Ash trees and their destructive reign continues. In this guest post, Dr. Dave Coyle, assistant professor at Clemson University, shares his insights on the EAB and how to deal with it. He was also a guest on the Green Industry Leaders Network podcast, Blurring the Tree Lines, discussing tree stress and pests like EAB, in urban, suburban and forest trees.

Where did EAB Come From?

Who would have thought that a little green beetle – not even an inch long – would cause billions of dollars in damage and lead to the death of millions of trees on this continent?  I mean, sure, it was always a possibility, but we’re currently living though one of the worst invasive species issues in our lifetime.

The emerald ash borer, (EAB for short, Fig. 1) was first discovered in 2002, but probably arrived in the late 1990, near Detroit, MI. It is now present in most of eastern North America (current distribution map) from APHIS.  The larvae or young of this beetle, feed on the phloem of ash trees (genus Fraxinus), and their feeding nearly always results in tree death.  Oh, and not just one type of ash tree – all of them: white, green, blue, pumpkin…if it’s a Fraxinusspecies, it’s susceptible to EAB. 

EAB on Corona Tools Blog

Figure 1. EAB adult.  Photo by Matt Bertone, NC State University.

How do I know if my Ash tree has EAB? 

If the tree starts declining, or losing foliage and branches, or has a sudden increase in woodpecker populations, they’re there trying to find and eat the EAB larvae, and often cause “ash blonding” (Fig. 2), your ash tree may have EAB.  

EAB2 on Corona Tools

Figure 2. Ash blonding.  Photo by David Coyle, Clemson University

It’s important to inspect your tree and look for little D-shaped holes (Fig. 3) – this is where the adults leave the tree once they’re fully developed.

EAB3 on Corona Tools

Figure 3. D-shaped holes made when EAB adults leave the tree.  Photo by David Coyle

Can I save my tree if it has EAB? 

Well that depends…if most of the crown still looks healthy, then probably.  There are many chemical treatments that work great to both prevent and treat EAB once a tree is infested.  There are biocontrol agents (other bugs that eat EAB), but these won’t usually save an individual tree – they’re good for keeping overall populations in check, and are most often used in natural areas.  It is important to note that in nearly all situations, treating a tree is cheaper than removing and replacing it.  And, trees provide many benefits.  The National Tree Benefit Calculator is a great resource to see the value of a tree.

The EAB Outlook

It’s difficult to determine exactly how many trees EAB has already killed, but the number is easily in the millions.  And, EAB is already present across much of eastern North America.  Will it get out West?  It’s likely...there’s already a population in Colorado.  Remember, by not moving firewood from place to place we can prevent the spread of EAB – this is one of the main ways invasive insects get transported to new places.  Our friends at have a lot of great resources on this topic.

The recent polar vortex had folks wondering if the cold temperatures might kill all the EAB.  I hate to burst your bubble (but I’m going to burst your bubble…), but the answer is no. Sure, in some places many EAB larvae likely died, but even this recent cold snap isn’t enough to kill all the EAB. Some died, yes – especially in colder areas like the northern U.S. and Canada.  But certainly not all of the EAB died.

Resources About EAB

InsideClemson_PicbyErinMurphyFor the latest resources on EAB, check out, a multi-state and multi-agency collaborative, and the great site by Purdue University. 

About the Author

Dr. Dave Coyle is an Assistant Professor in the Department of Forestry and Environmental Conservation at Clemson University.  He can be found on Twitter @drdavecoyle and Instagram. And listen to Dave's podcast, Blurring the Tree Lines, on the Green Industry Leaders Network.

Topics: #treechat, gardening, trees

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