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

Figure 1. The emerald ash borer adult is a bright, metallic green beetle, about ½ inch long.

Figure 1. The emerald ash borer adult is a bright, metallic green beetle, about ½ inch long.
Photo by Matt Bertone, NC State University.

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? The emerald ash borer (EAB for short, Fig. 1) was first discovered in 2002 (but probably arrived in the late 1990s) near Detroit, MI, and is now present in most of eastern North America (current distribution map from APHIS: https://www.aphis.usda.gov/plant_health/plant_pest_info/emerald_ash_b/downloads/MultiState.pdf). The larvae (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 Fraxinus species, it’s susceptible to EAB.

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 trying to find and eat the EAB larvae, and often cause “ash blonding”, Fig. 2), your ash tree may have EAB. 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.

Figure 2. Ash blonding refers to the lighter areas on the trunk where woodpeckers have knocked off the outer, darker ash bark in search of EAB larvae.

Figure 2. Ash blonding refers to the lighter areas on the trunk where woodpeckers have knocked off the outer, darker ash bark in search of EAB larvae.
Photo by David Coyle, Clemson University.

Figure 3. D-shaped holes made when EAB adults leave the tree.

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

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 (link: http://www.emeraldashborer.info/documents/Multistate_EAB_Insecticide_Fact_Sheet.pdf). 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.

Remember, we can prevent EAB by not moving firewood from place to place – this is one of the main ways invasive insects get transported to new places. Our friends at https://www.dontmovefirewood.org/ have a lot of great resources on this topic.

Want more information on EAB? Check out http://www.emeraldashborer.info/, a multi-state and multi-agency collaborative, and the great site by Purdue University: https://extension.entm.purdue.edu/EAB/.

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), Instagram (drdavecoyle), or through email at dcoyle@clemson.edu.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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