Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern & Central Midwest
October, 2004
Regional Report

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The emerald ash borer may be lovely but it can devastate ash trees. (Photo courtesy of

Beware the Emerald Ash Borer

Emerald ash borer -- sounds somewhat attractive, doesn't it? This devastating imported beetle was first discovered in the U.S. in 2002, and since then it has killed over 8 million white and green ash trees in 13 counties in Michigan. Isolated infestations have been found in nearby Canada, Indiana and Ohio. It has already cost tens of millions of dollars to Michigan nurseries, landscapes and woods. Many experts believe that if this borer is not contained and eradicated, it will have an impact similar to that of Dutch elm disease and chestnut blight.

This borer attacks all species of ash (Fraxinus) but not mountain ash, which is a different genus altogether (Sorbus). The beetle is a beautiful, metallic green and about half an inch long. The female lays eggs in bark cracks or on the bark surface in midsummer. When the larvae hatch, they burrow into and feed on the wood, interrupting nutrient and water flow to the tree. The larvae overwinter in the tree and then pupate in spring. Soon afterward the adult beetles emerge through small D-shaped holes.

A beetle infestation causes thinning of the crown of a tree and branch dieback, which weakens the tree. A severe infestation can kill a tree within two to four years. Woodpeckers are important predators of this borer, so increased woodpecker activity can be a good indicator of an infestation.

Currently the counties with substantial borer damage have been quarantined so that no ash products except chips less than an inch in size can be transported away from these counties. This will help prevent the spread of the borer in firewood.

Unfortunately, there is no way to tell when healthy trees have borers in them, so it has been a practice to remove all ash trees within a certain radius of confirmed infestations. Certain insecticides have proven to be effective, although they are not necessary outside a two-mile radius of a known infection.

How can you avoid this problem? How can you help? First of all, it's critical to be observant. Learn to recognize the species of ash in your area, and learn what a healthy tree looks like. If you notice any decline, notify your local county extension agent and local Department of Natural Resources agency. This devastating problem may be transported to other areas of the Midwest if we don't educate ourselves and take every precaution to prevent its spread.

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