US National Arboretum


Emerald Ash Borer Update

Ash decline - Emerald Ash Borer The emerald ash borer has killed more than twenty-five million trees (see image at right of trees in decline), and in spite of tens of millions of dollars spent on control measures, this introduced exotic pest is spreading to an ever widening area. The emerald ash borer will have a major impact in all locales where ash trees are dominate, either as landscape and street tree specimens or in native woodland populations. In North America, the emerald ash borer attacks only ash trees, primarily white ash (Fraxinus americana) and green ash (F. pennsylvanica) and their many cultivated varieties. Their native range covers two-thirds of the continental United States, from Montana to Maine, south to Florida and Texas. Because ash trees are fast growing and adapted to growing in alkaline soils, they are widely planted throughout the United States including all the western states. It is currently unclear if native western ashes, Oregon ash (F. latifolia), native from British Columbia to southern California, and Arizona ash (F. velutina), are also susceptible to emerald ash borer and may be attacked as well.

Adult ash borer This Asian beetle, beautifully iridescent green in color (see image at left), was discovered in Michigan in 2002. It is believed to have been imported in wooden pallets and may have been undetected for more than ten years. By 2005, the emerald ash borer had spread to Ohio, Indiana, and Illinois, with an isolated outbreak in Maryland. This pest continues to extend its range, now established in western Pennsylvania and most recently in Fayette County, West Virginia. While other ash boring insects seem to infect weak or dying trees, the emerald ash borer can infect large healthy trees, killing them within one to three years. This beetle can devastate an area physically and economically. One small city in Michigan removed over 2,000 dead or dying large ash trees at a cost of 2 million dollars. The economic impact of this borer will end up totaling billions of dollars.

Emerald Ash Borer larva Lifecycle of the Emerald Ash Borer
The 1/2 inch adult beetles emerge in late May and June in warm climes of the Mid- Atlantic region, June and July in the Midwest and live about three weeks. Females lay eggs on crevices in the bark. After hatching, larvae chew through the bark (see image at right) to the inner bark areas, called the cambial layer. The larvae feed in this area making S-shaped tunnels or galleries, which eventually become larger and quite extensive. Since the cambium layer is the site of new wood and bark production, as well as nutrient and water transport, larval feeding in this area is lethal to the tree. Larvae pupate in late spring and adults emerge in summer from D-shaped exit holes in the bark.

Exit Hole Damage.jpg Symptoms of Emerald Ash Borer
Usually trees are not diagnosed with emerald ash borer until severe dieback in noticed. Whole branches wilt and die and the tree re-spouts below the dead areas. The D-shaped exit holes (see iamge at left) distinguish this borer from other insects that attack ash trees. If you suspect your tree is infected, please call your county Agricultural Extension office.

Please remember that the new infestation sites are areas along major interstate highways and it is believed that illegal transporting of ash firewood is the major cause of these new outbreaks. People are giving emerald ash borer larvae a free ride to new unaffected areas inside firewood. The best way to slow down the rapid spread of emerald ash borer is to leave your firewood at home.

- More Emerald Ash Borer information:

  • For specific information about a multistate effort in Michigan, Illinois, Indiana, Maryland, Ohio, Pennsylvania, and Wisconsin (uninfested) to bring you the latest information about emerald ash borer, visit this web site.
  • For additonal general information about the insect and other disease resources, visit the US Forest Service pages here.
  • Sources of images used in this web page:
    - Ash decline, courtesy USDA Forest Service;
    - Ash Borer adult, David Cappaert of MSU (courtesy;
    - Larva, Michigan Dept. of Agriculture (courtesy;
    - Exit Hole (courtesy

- For more information about other plant pests and how to control them:

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Last Updated  September 4, 2011 3:40 PM

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