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Emerald ash borer (EAB), Agrilus planipennis, is a very destructive insect pest of ash trees (Fraxinus spp.). It is native to Asia, including China, Japan, Mongolia, Korea, the Russian Far East and Taiwan. It was first found in North America in southeast Michigan in 2002, although it had likely been present since the early 1990's. EAB has since been found 13 states and two provinces in Canada (as of March, 2010). It was first found in Minnesota in St. Paul in May, 2009. As of March, 2010, EAB has only been confirmed in several adjacent locations in St. Paul and Minneapolis.
All species of ash are attacked, including all ash species found in Minnesota: green (F. pennsylvanica), black (F. nigra), and white ash (F. americana). Mountain ash (Sorbus spp.) is not a true ash and is not attacked. Ash of all sizes from one inch diameter to large mature trees are attacked. EAB prefers unhealthy, stressed trees but will also attack healthy ones as well.
Native ash have not demonstrated any resistance to EAB, placing essentially all ash at risk from EAB. There are about 937 million ash trees in Minnesota, one of the largest concentrations of ash in the United States. Not only are ash abundant in our forests, but they are also an important component of our urban landscapes.
Emerald Ash Borer
Jeffrey Hahn, University of Minnesota
EAB is a slender, elongate insect about 1/3 - 1/2 inch long. It is widest just behind the head, gradually tapering back to the abdomen. It is a bright iridescent green to copper-green color, often with a copper colored area behind the head. Its body underneath the wings is a purplish-magenta color. See also Insects that may be confused for EAB (PDF).
EAB galleries in infested tree
Jeffrey Hahn, University of Minnesota
Trees can be killed in one to four years. When trees are first attacked by EAB, the foliage starts to thin in the crown and dieback begins to be apparent. Eventually, there is severe dieback and little foliage. Unfortunately, a thinning crown is not diagnostic of EAB as other problems can also cause similar symptoms.
Infested trees are often attacked by woodpeckers. Patches of bark removed by woodpeckers can be a good sign of the presence of EAB. Vertical splits in the bark due to callous tissue forming over old galleries may also be seen, although bark can split for other reasons.
When the adults emerge, they create small, 1/8 inch D-shaped exit holes that are characteristic of this insect. Although characteristic of EAB, these exit holes are often challenging to find. If you remove the bark on ash showing EAB symptoms, look for the characteristic S-shaped larval galleries. See also Signs and Symptoms of the Emerald Ash Borer (PDF).
First, use the diagnostic page, Do I have emerald ash borer? (PDF), to see if you can clearly rule out EAB. If, after you have gone through this page, you cannot easily rule out EAB, then contact the Forest Resources Extension and Outreach to find a volunteer EAB First Detector near you. You can also contact the Minnesota Department of Agriculture on their Arrest the Pest Hotline at 651-201-6684 or 1-888-545-6684 to report your suspicions.
Currently Ramsey, Hennepin, and Houston counties are under a state and federal quarantine. This quarantine prohibits the movement of any hardwood firewood, as well as ash branches and limbs and similar material, out of these counties (and any counties in the future that are declared to be under quarantine) to help prevent the movement of EAB. Ash branches, limbs, and other wood debris need to be taken to appropriate disposal sites. If you live in a county that is presently not under quarantine, there are not any restrictions in moving or disposing of ash wood. It is strongly recommended to not move ash material and to buy firewood from local sources. For more information concerning the quarantine, call the Arrest the Pest Hotline, 651-201-6684 or 1-888-545-6684.
When weighing whether to treat your ash tree, there are a number of factors to consider, such as are you within 15 – 20 miles of a known infestation, how healthy is your ash, how many trees do you have, the value of the ash, and weighing the cost of treating your tree regularly (every one to two years) versus the cost of removing and possibly replacing the tree. The action you take will be different for different homeowners. See also Insecticide Options for Protecting Ash Trees from Emerald Ash Borer (PDF).
There are a variety of trees that are suitable and available to replace ash in the landscape. The specific trees that are appropriate will vary by the region in which you live. See the Recommended Trees Series.
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