Extension Logo
Extension Logo
University of Minnesota Extension

What You Should Know About Emerald Ash Borer

Emerald ash borer (EAB) is native to East Asia and was discovered in Detroit, Michigan and Windsor, Ontario in 2002. Indications are that it may have been introduced to this area as early as 1990 by means of infested wood packing material from Asia. EAB has spread rapidly across the eastern United States due to the long-distance movement of infested ash firewood, nursery stock and other ash materials. On May 14, 2009, EAB was discovered in the South Saint Anthony Park neighborhood in St. Paul, MN. 

Why is this important?

EAB kills ash trees! All ash trees (Fraxinus spp.) are susceptible to EAB. (Mountain Ash is not a true Ash, but rather, it is in the Rosaceae family.) Millions of ash trees have already been killed across the Midwest, eastern United States, and Canada. Minnesota has the highest volume of ash trees in the U.S. with nearly a billion forestland and urban ash trees combined. The potential for economic and environmental impacts of losing these trees is significant. 

Most of the emerald ash borer life cycle takes place below the bark. EAB larvae feed on the inner bark of ash trees and cut off the water, and nutrient conducting vessels, causing tree death. Woodpeckers readily look for larvae feeding beneath the bark, and often reveal infested trees during the winter months. These trees become covered in light-colored "flecking" as woodpeckers remove the outer bark.  As tunnels (called galleries) from feeding larvae accumulate and disrupt the flow of a tree's nutrients, trees begin to show signs and symptoms of the infestation. Once symptoms have started to show, trees generally die within one to three years. Emerging adult beetles chew characteristic 1/8-inch-wide, D-shaped exit holes that can be useful in confirming infested ash trees. Because the holes are small and frequently high in the tree, they can be difficult to find.

So how do you know if EAB is the cause of your ash tree problems? The MN Department of Natural Resources recommends looking for these symptoms:

  • Canopy Dieback: tree begins to die, shedding leaves from the top 1/3.  This progresses to the bottom until the tree is bare.
  • Epicormic Shoots: branches growing from the roots and trunk with leaves often larger than normal.
  • Serpentine Galleries: Larval feeding marks under bark and on trunk that weave back and forth across the woodgrain and are often packed with frass (mix of sawdust and excrement).
  • Bark splitting: Vertical splits in bark.  Galleries can be exposed under bark split
  • Increased woodpecker activity and damage: Several woodpecker species feed on EAB larvae/pupae and peck outer bark while foraging, creating large holes when extracting insects.

What should you do if you see a green bug in your yard?

There are many green bugs out there that can be confused with EAB. The adult ash borer is ½” long with bright metallic wings that cover a purple, segmented abdomen.  They are widest at the head, and thin to a point at the end. Larvae are creamy white and legless with a flattened, bell-shaped, segmented body. Other bugs you are likely to see are 6-spotted Tiger Beetles, Japanese Beetles and Bronze and Chestnut Borers.

How do you know for sure?

If you are still uncertain if you have EAB, contact your local extension office.  Douglas County residents can reach me at 320-762-3890 or at trot0053@umn.edu.  Take pictures of the bugs you find and any damage you notice.  You can also access many identification resources at https://extension.umn.edu/tree-and-shrub-insects/emerald-ash-borers.

Page survey

© 2023 Regents of the University of Minnesota. All rights reserved. The University of Minnesota is an equal opportunity educator and employer.