The Gift That Keeps on Giving

Contact: Colleen.Kenny, MD Dept. of Natural Resources – Forest Service |

Emerald ash borer adult. Photo: Leah Bauer, USDA Forest Service Northern Research Station,
"D"-shaped exit holes on ash trees are a good indication of EAB infestation.(Cropped) Photo: Kenneth R. Law, USDA APHIS PPQ,

ANNAPOLIS, MD (April 01, 2016) – The emerald ash borer (EAB) is an invasive beetle that has been in Maryland since 2003 and continues to increase its range throughout the state. Since the original detection in Prince George's County in 2003, the beetle has spread throughout all of Southern, Central, and Western Maryland, and was found for the first time on the Eastern Shore in 2015. EAB attacks all species of native ash trees, killing as much as 99% of untreated trees. Dying trees pose a significant threat to public safety, and to the health of our urban tree canopies and forests. Although the beetle doesn't emerge until May, April is when ash trees begin to leaf out and EAB damage may be visible in infested trees. For this reason, the Maryland Invasive Species Council has named EAB as its April Invader of the Month.

In its adult stage, EAB is a metallic-green beetle that is about 1/2 inch long. EAB emerges throughout May and June to feed, mate, and lay eggs on ash trees. Within two to three weeks, newly hatched larvae bore into ash trees, where they spend most of the year hidden under the bark. EAB is difficult to spot; signs that an ash tree may be infested could include crown dieback, epicormic sprouting, "D"-shaped exit holes, serpentine feeding galleries below the bark, bark splitting, and woodpecker damage.

Since its original detection in Detroit, MI in 2002, EAB has invaded 25 states, as well as Ontario and Quebec, Canada. The beetle has killed millions of trees; some estimates are as high as 25-50 million trees. Some of the EAB spread can be attributed to normal insect movement, but much is human assisted, including the transport of infested firewood and nursery stock. Due to the spread of EAB, the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service has enacted a federal quarantine (see link below). The quarantine allows for free movement of ash material within its boundaries. Due to the recent spread of EAB to the Eastern Shore, the entire state of Maryland is now under the federal quarantine.

EAB dieback
Crown dieback and epicormic sprouting.
Photo: Daniel Herms, The Ohio State University,
EAB bark
Woodpecker damage of infested tree.
Photo: Kenneth R. Law, USDA APHIS PPQ, (cropped) 

Maryland has more than 5 million ash trees. Many line our streams and rivers, helping to filter out sediment and pollutants from our water. Ash trees are also commonly planted along streets and lawns, providing shade and air quality benefits in urban areas. As EAB moves across Maryland, all of these trees are at risk along with the benefits they provide. When these trees die, they may become very brittle and snap within a few months, posing a serious safety hazard. In response to the ecological and public safety threats posed by EAB, a host of tools is being used in the fight to manage this devastating pest.

Chemical treatments are available and effective for protecting healthy trees. Trunk injections of emamectin benzoate are currently the most effective option and last two years. This method must be done by a licensed pesticide applicator. It is effective but expensive to treat large numbers of trees, particularly since they need retreatment every year or two.

The Maryland Department of Agriculture (MDA) continues to do the trapping surveys for EAB that it has done since the beetle was first discovered here, concentrating on the counties where infestations have not yet been found. In 2015, MDA placed 130 traps throughout the state. As new "positive" areas are found in Maryland, we launch our best long-term defense: biological control (biocontrol). USDA has approved the use of four biocontrol agents to help in the fight against EAB. These biocontrol agents are small parasitoid wasps that come from Asia, where they have evolved to parasitize EAB. All of the biocontrol agents work against EAB in the same way. They lay their eggs on or in EAB eggs or larvae. When the wasp eggs hatch, the wasp larvae devour the EAB egg or larvae, preventing EAB from surviving to reproduce. A total of over 323,000 biocontrol wasps have been released in 36 sites throughout Maryland. The hope is that, in time, these tiny wasps will help reduce the populations of EAB to a very low, tolerable level.

Maryland is attacking this ash-destroying beetle in many ways and will continue this fight into the foreseeable future. Will we ever get rid of EAB? Probably not. But we hope to be able to introduce tools that will slow its spread, reduce the numbers of this destructive pest, and help our ash trees to survive.

For more information about other Invasive Species of Concern in Maryland, visit the Maryland Invasive Species Council or call the Maryland Department of Agriculture at 410-841-5920.

Tetrastichus planipennisi, one species of parasitoid wasp released in Maryland to target EAB. Photo: David Cappaert, Michigan State University,

photos available electronically on request.

For more information on the Internet:

Emerald Ash Borer Information Network.
Emerald Ash Borer, Maryland Department of Agriculture.
Emerald Ash Borer Reports (Map), Cooperative Emerald Ash Borer Project.
Federal EAB Quarantine (Map), Cooperative Emerald Ash Borer Project.
Emerald Ash Borer, USDA Animal and Plant Health Inspection Service.