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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

B’more Battles the Beetle: Emerald Ash Borer, Agrillus plenipennis


Beautiful, but deadly, an Emerald Ash Borer emerges from a tree after completing larval development.


Back in 2011 Bug of the Week reported the escape of the Emerald Ash Borer, a.k.a. EAB, from a federal quarantine zone in Prince George’s and Charles counties, MD. This nefarious killer of ash trees has now been found in almost every county in Maryland west of the Chesapeake Bay. Nationwide it has killed more than 100 million ash trees since it was first detected near Detroit, Michigan in 2002. It now occupies parts of Arkansas, Colorado, Connecticut, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Massachusetts, Maryland, Minnesota, Missouri, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, Wisconsin and two provinces in Canada.  

Legless Emerald Ash Borer larvae like these two are easily moved in firewood, logs, or branches.

EAB likely arrived in this country in packing material from Asia. In 2003 the first EAB tremor was felt in our region when the borer was detected in a nursery in Prince George’s County. This detection confirmed the suspicions and fears of many, namely, that the EAB could be transported and relocated with infested nursery stock. Ash trees infested with EAB were illegally shipped from an out-of-state quarantine zone to a Maryland nursery just south of Washington, DC in April, 2003. During the spring and summer beetles moved from infested Michigan-grown trees to ones grown in the nursery. Some of these trees were shipped and installed in several locations in the greater Washington, DC area.  

Officials from the Maryland Department of Agriculture in cooperation with the USDA conducted search and destroy missions. In 2003, more than 1000 ash trees were destroyed in an attempt to eradicate this pest. State officials were optimistic about the results of the eradication program until August 21, 2006 when larvae of EAB were detected in ash trees in and near the original eradication area. What this meant was that beetles somehow escaped the first eradication attempt and established an infestation in native ash trees nearby. Reminiscent of Jurassic Park, yes?  


Since its arrival in the US, Emerald Ash Borer has killed hundreds of millions of ash trees. Estimated management costs, lost property values and lost revenues from timber exceed 1.6 billion dollars annually.

Emerald Ash Borer larvae create serpentine galleries beneath the bark. By consuming cambium, phloem, and sap wood, the borer effectively girdles the tree condemning it to death.

Beetles were apparently on the loose for about four growing seasons before the beast was rediscovered in 2006. On August 22, 2006 the Maryland Department of Agriculture issued a revised Quarantine Order that prohibited anyone from moving ash trees, ash products, or any hardwood firewood into or out of Prince George’s County until further notice. In 2008, this rascal jumped the southern border of Prince George’s County and was discovered a few miles away in northern Charles County. Using historical data provided by the Maryland Department of Agriculture, we were able to estimate the natural rate of spread of EAB to be just under one mile each year, nearly twice the ½ mile per year scientists had previously believed that this pest could fly. At this rate of spread, it would have taken the beast almost 30 years to move from its introduction point in Prince George’s County to Baltimore. However, once again EAB escaped the quarantine, possibly through the movement of infested firewood, and was detected in Howard and Anne Arundel counties in 2011. With the detection of EAB in Howard County, our initial projections were out the window, and our revised models put the green menace in charm city in less than 10 years. Now in 2015 this vision has become reality. The bad beetle is in B’more.  

Why is this news so discouraging? Here are the reasons. According to the Maryland Department of Natural Resources, ash trees are the most common tree in Baltimore where the population stands at something north of 290,000 trees. Perhaps more disturbing is the fact that when the entire metropolitan area surrounding Baltimore is considered, the total population of ash exceeds 6 million trees. According to estimates by USDA the loss of ash trees in Baltimore could exceed $200 million dollars.  

Why are ash trees so valuable especially in urban forests? Most people don’t appreciate the many benefits that accrue from trees in our cities and suburbs:

  • By virtue of their shade and evapotranspiration, trees cool cities and the loss of this ecosystem service drives up summer cooling costs dramatically.
  • Trees intercept rainfall, slowing its movement and allowing water to infiltrate the soil, thereby mitigating surface water runoff and protecting the Bay.
  • Photosynthesis uses carbon dioxide as a raw material. Trees are vital for fixing carbon and removing it from the atmosphere, thereby helping to mitigate climate change.
  • Trees in cities also remove pollutants from the air and help beautify our urban areas, adding significantly to property values.
  • Recent studies demonstrate a link between the presence of urban trees and improved human health, including faster recovery times of patients in hospitals and reductions in rates of heart disease.
  • Ashes are also a common native tree in watersheds in Maryland’s piedmont, where they provide shade and nutrients to our riparian and woodland ecosystems. Ashes provide food and shelter to more than 20 species of indigenous native creatures. Collectively, these organisms are valuable members of several ecological communities. They help the natural world go around.  

Dieback in the canopy and heavy activity by woodpeckers are two strong indicators that an ash may be infested by Emerald Ash Borer.

As far as we know, EAB attacks all native species of ash and also non-natives used for ornamental purposes in landscapes. Black ash and green ash appear to be the most susceptible to this pest and mortality of these species is a near certainty unless they are protected by insecticides. Other species of ash, such as blue and white ash, are more resistant, while the Asian host of EAB, Manchurian ash, exhibits high levels of resistance. In North America it is estimated that some 8 billion ash trees populate our lands. We once believed that only members of the ash clan were on the menu for this beast. Unfortunately, we recently learned that our beautiful native fringe tree can also serve as a host for this killer.  

Since its detection in the Midwest in the early 2000’s, much has been learned about managing this pest in cities and suburbs. EAB tends to roll over the urban forest like a great tsunami, doubling the number of ash trees killed in a city each year once it becomes established. In a period of eight to ten years, tree mortality rises from 1 or 2 percent to 100 percent if intervention does not take place. Early infestations of EAB often went undetected and cities were forced to remove dead and dying trees at enormous expense to municipal budgets. While some municipalities are still opting to remove all ash trees when EAB is detected, experts are now recommending a hybrid approach of removing smaller or less healthy ash trees that provide fewer ecosystem services and are less valuable, while protecting larger and high value trees with insecticides. Clever analysis by Cliff Sadof of Purdue University and Rich Hauer of the University of Wisconsin have demonstrated that this hybrid approach of removing some trees and protecting others minimizes the cost of management while preserving the benefits of urban forest ash trees. A similar analysis performed for three municipalities including Annapolis, Maryland, yielded the same result.  

The Emerald Ash Borer adult leaves behind a “D” shaped exit hole in the bark of the tree. This is a good clue for diagnosing the presence of this pest.

Many cities are developing EAB response plans and some have already put these plans into action. All municipalities in Maryland should start planning now for the almost certain arrival of this pest. The first step is, of course, to conduct a tree inventory of the municipality to determine the size of the ash population and its value. Next, plans should be made to determine the costs of tree removal, replacement, and treatment to decide which the best options are. We use the wonderful on line software packages i-Tree, EAB Cost Calculator, and EAB Planning Simulator to help in this planning process (see links below). An effort to manage the green menace is also underway in Maryland and other states that involve the release of tiny parasitic wasps that attack and kill larvae and eggs of EAB. To learn more about this approach, please visit the May 31, 2010 Bug of the Week episode entitled “Parasitoids to the Rescue.”

 If your plant identification skills are a little rusty or if you suspect that one of your ash trees is infested by EAB, please visit the Home and Garden Information Center’s EAB web page. It contains valuable links including one that will help you identify the ash trees in you landscape. Information on how to report a suspected EAB infestation is also available at this site:  

Maryland’s cities, including B’more, now face weighty decisions regarding how they will manage their valuable ash resources in the face of this egregious and lethal pest. 


The references “Emerald Ash Borer Invasion of North America: History, Biology, Ecology, Impacts, and Management Approaches” by Dan Herms and Deb McCullough; “Predicting the Movement and Potential Economic and Ecological Impacts of the Emerald Ash Borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), in Maryland Municipalities and a Discussion of Possible Management Options” by C. Sargent, H. M. Martinson, R.A. Bean, S. Grimard, B. Raupp, S. C. Bass, E. J. Bergmann, D.J. Nowak, and M. J. Raupp; and “Direct and indirect effects of alien insect herbivores on ecological processes and interactions in forests of eastern North America” by K. J. K. Gandhi and D.A. Herms, were used in preparation of this episode. Excellent webinars by Deb McCullough, Cliff Sadof, and Rich Hauer at the web site below were also used.  

To learn more why it may be more cost effective to treat trees than remove them, please listen to the webinar at this site:

 Web based tools to estimate benefits of ash trees and costs associated with managing EAB can be found at the following links:

 To learn more about EAB in Maryland and throughout the US, please visit these sites: