Pests & Diseases: Emerald Ash Borer

Park Cultural Landscapes Program

Updated Cultural Landscapes

The Emerald Ash Borer (Agrilus planipennis Fairmaire) was identified in North America in 2002, most likely after it was accidentally transported from its native Asia in wood packing material. Emerald Ash Borer (EAB) has caused ash tree decline across the Midwestern and Northeastern United States. The beetle is the most destructive forest insect introduced to the continent in recent history and is now impacting 31 U.S. states and two Canadian provinces.

Identifying an Infestation

The Emerald Ash Borer (EAB) targets green, black, and white ash trees. The ½ inch-long, metallic green adults nibble on the ash tree foliage, but they do not cause much damage to the trees.

The EAB is most destructive during the insect’s early stage of life. When the larvae feed on the inner bark, it limits the tree’s ability to transport water and nutrients, and the dead trees quickly become brittle.

The insects leave a D-shaped hole in the bark when they emerge as adults in the spring. Affected trees may also exhibit bark splitting and epicormic shoots (or water sprouts) growing from the roots and trunk. Woodpeckers eat the EAB larvae, so heavy woodpecker damage on ash trees may be another sign of infestation.

What to Do About the EAB?

The beetle’s distribution is largely due to individuals and businesses transporting infested nursery stock, firewood, or unprocessed logs. Because of its impact, Federal and State agencies like the USDA enforce quarantines and fines to regulate the transport of wood products.

There is no known cure once a tree is infected, and most ash trees succumb to the beetle’s effects within 3-6 years after infestation. With a nearly 100% mortality rate, preventing the spread of EAB is critical.

Map of the United States and Canada with green states indicating the spread of Emerald Ash Border by 2017
Spread of EAB by 2017. Click on the map for full timeline (Source: EAB Information Network)

To help limit the spread of the beetle, you can:

  • Understand the signs and risks of infestation
  • Share information with staff and visitors, and
  • Don’t move firewood from impacted areas.
Forest monitoring and management
Early detection and quick response are important steps in addressing new infestations. Regularly monitor high risk areas and respond with prompt, interagency action where the EAB is identified. EAB management actions can be a part of broader forest or landscape management plans.
Mitigate danger from hazardous trees
Dead ash trees quickly become hazardous. Provide staff with training on hazard tree identification and management. Remove and remediate dead or dying ash trees, particularly in places that are commonly traveled by visitors or employees.
Restore healthy forests
The EAB has significantly reduced the number of ash trees across several regions of North America, and our current ability to eradicate infestations is limited. Rehabilitate forest ecosystems by promoting and restoring healthy, sustainable urban and rural forests. Consider options for using salvaged ash trees and planning for long term management of ecosystem functions – with or without ash trees.

A Case Study

Theodore Roosevelt Island, part of the George Washington Memorial Parkway in Washington, DC, was closed for several weeks in the summer of 2017 while park staff removed hazardous, diseased trees along the park’s trails.

Trees on the island have both cultural and natural value. The Olmsted Brothers firm helped to establish a forest on Roosevelt Island over a period of fifteen years, developed as a living memorial to Theodore Roosevelt. The plan featured meandering paths through a mature, native forest, envisioning visual connections to surrounding memorials with a feeling of sanctuary.

Black and white photograph of Civilian Conservation Corps workers clearing brush among trees on Theodore Roosevelt Island
Members of the CCC clear vegetation (NPS Photo)

In the 1930s, members of the Civilian Conservation Corps (CCC) cleared the island of most of its non-native vegetation and planted native hardwood trees and shrubs to fill gaps in the existing native forest. Over 35,000 plants were added to the island at this time. Ashes (Fraxinus sp.) were among the dominant large trees that Frederick Law Olmsted, Jr. selected for the forest.

Other parks of the National Capital Region have been significantly impacted by EAB infestation. Where park cultural landscapes have lost ash trees, compatible substitute trees can be planted. Examples of other native or specimen hardwoods are tulip poplar and willow oak.

Additional Resources

Can’t find what you need?   Contact the Park Cultural Landscapes Program via email or the program lead in your region.

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