All About Emerald Ash Borer

Learn more about the emerald ash borer, an alarmingly destructive beetle that is slowly moving across the United States and destroying many ash trees in its path.

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Fast-growing ash are common residential and community park trees.

Once a common and easy-to-grow tree in the eastern Midwest, ash trees are now greatly reduced in Michigan, Ohio, Indiana and surrounding states. Decades old specimens as well as young saplings have fallen to an invasive pest commonly called emerald ash borer or E.A.B.

This destructive beetle hitchhiked from Asia where it has long infested ash trees. It slowly gained foothold in North America and is now moving across the central United States infesting all types of ash trees—green, white, blue. All members of the Fraxinus species are susceptible to attack.

E.A.B. is a very small, metallic green beetle. The adult beetles feed on ash leaflets while the immature larvae feed underneath the bark on the living tissue inside the tree. As the larvae feed, they cut of the tree's supply of nutrients, minerals, and water. This causes a slow decline that results in tree death in two to four years after the tree is infested. There are few effective controls to stop the beetles' destruction.

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Emerald Ash Borer ID

Emerald ash borer. Photo by Leah Bauer, USDA Forest Service Northern Research Station, Bugwood.org

Emerald ash borers are ½-inch-long, bright metallic green insects that are rarely seen. They feed on leaves and are active in the summer months. The white worm-like larvae feed under the bark of an ash tree, boring s-shaped tunnels as they move through the tree.

Signs and symptoms

E.A.B. creates these d-shape holes in bark when it exits a tree. Photo provided by Pennsylvania Department of Conservation and Natural Resources—Forestry Archive, Bugwood.org

Often ash trees exhibit signs of infestation before the pests themselves are noticed. Canopy dieback is a sign of infestation. Dieback begins in the top one-third of the canopy and progresses during subsequent growing seasons until the canopy is bare. The tree might also produce vigorous shoots at ground level and the new leaves are usually larger than normal.

Close inspection of the bark might reveal unique "D" shape exit holes. The larvae create these holes when they emerge from the bark. Peel away a bit of the bark and you might see serpentine feeding galleries.

Increased woodpecker activity is also a potential sign of infestation. The woodpecker is searching out beetle larvae.

Disease prevention

When adding new trees to your landscape, do not plant ash. Even if E.A.B. is not prevalent in your area, entomologists predict that it will slowly move across the United Steas., destroying most ash trees in its path. Instead of an ash tree, choose a species that is native to your area. A local garden center or your state DNR can provide recommendations.

The best weapon asgainst E.A.B. is a healthy tree. Follow these tips for promoting healthy trees.

  • Avoid compressing the soil around tree roots. Do not park on the root zone of a tree and minimize construction around the root zone.
  • Protect the trunk from injury by spreading a 2-inch-thick ring of mulch around the base of the trunk. The mulch will suppress weeds and limit potential injury from weed whips and lawn mowers.
  • Water young trees using a drip hose during extended periods of dry conditions.

Disease management and treatment

Serpentine feeding galleries like these are a sign that E.A.B. has already infested your tree. Treatment is not recommended. Photo by Pennsylvania Department of Conservation and Natural Resources—Forestry Archive, Bugwood.org.

There is no sure-fire method of protecting an ash tree from infestation, nor is there a guaranteed cure for infested trees. There are several treatments on the market with varying success rates. Here are a few things to know before you invest in a chemical control strategy.

  • Most insecticide controls must be used yearly for the life of the tree. This is a long-term control regimen.
  • Insecticide treatments may not be effective in controlling E.A.B. in your ash tree. Storm damage, other injuries to the tree, soil moisture, and a host of other factors influence the effectiveness of these products.
  • Treatments are most effective as prevention, before E.A.B. finds your tree.
  • Treatments are suggested only if you live within 15 miles of a confirmed E.A.B. infestation. Known infestations are recorded at www.emeraldashborer.info/.
  • Consult your local Extension service for recommended chemical controls in your area. Experts will provide accurate applicaiton methods and specific application timing to prmote effective use of the chemicals.
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