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Emerald Ash Borer

September 29, 2004

An insect new to North America, emerald ash borer, Agrilus planipennis, attacks and kills healthy ash trees. It is closely related to the bronze birch borer, so its damage, appearance, exit holes, and biology are similar to that pestís except that it attacks healthy ashes rather than birches in at least the early stages of decline. Its native range includes China, Korea, Japan, Mongolia, the Russian Far East, and Taiwan. In the United States, it was first identified in the Detroit, Michigan, area in July 2002. Since then, it has also been found in other areas of Michigan, the Toronto, Canada, area, areas of Ohio, and other locations outside the Midwest.

Adult beetles are 1/3 to 1/2 inch long and elongate, with metallic emerald green wing covers on a bronze body. They emerge primarily in late spring through 1/8-inch-wide, D-shaped holes in the bark of ashes. Adult beetles are present through June into mid July. After mating, the female inserts her eggs, one or two at a time, between bark flakes.

Eggs hatch into larvae that tunnel through the bark into the cambium, where the water-, nutrient-, and sugar-conducting tissues, the xylem and phloem, are located. The larvae are white, elongate, and flattened, growing to about 1-1/2inches long. The larvae pupate in the cambium and emerge the following spring.

The larvae create slender, winding tunnels that frequently wind back and forth, creating a series of S shapes that run into one another. Just as commonly, the tunnels meander under the bark with no particular pattern. As the tunnels become numerous, they effectively girdle the branch, causing the branch to die due to lack of water and nutrients.

Emerald ash borer attacks at the top of the tree first, causing dieback of the top. Attack continues down the tree, resulting in the gradual death of branches, and the tree dies in 2 to 3 years. The bark on attacked trees separates from the trunk, allowing the larval tunnels to be easily seen. Once the tree dies to the ground, suckers form around the base of the trunk.

The Morton Arboretum in Lisle, Illinois, sponsors an Illinois emerald ash borer readiness group, whose purpose is to prepare the state for the pestís possible occurrence. The group consists of representatives of various municipal, state, and federal organizations; professional horticultural groups representing nurserymen, landscapers, and arborists; and other appropriate professional organizations. Included on that group is Charles Helm of the Illinois Natural History Survey and James Appleby and Philip Nixon from the University of Illinois. These three entomologists are surveying Illinois for the borer and providing educational information about this insect across the state.

Surveys in Illinois have consisted primarily of inspecting dead and dying ash trees in various regions of the state. Illinois Department of Agriculture (IDA) nursery inspections have incorporated close scrutiny for emerald ash borer. Reports from landscape professionals and the public about dying ash trees are followed more closely by IDA and University of Illinois Extension, with site visits being more common. In some states, surveyors are placing sticky traps on ash logs and girdled ash trees to attract and catch any emerald ash borer beetles in the vicinity.

It is thought that emerald ash borer is most likely to enter Illinois by people bringing in young ash trees from infested areas or bringing in firewood from those areas. To help prevent this, billboards asking people not to take firewood from Michigan have been placed along interstate highways leaving the state.

The commercial sale and movement of nursery stock from infested areas has been forbidden through federal quarantine, making it unlikely that the borer will be brought into the state through the nursery trade. However, in other states, infestations of emerald ash borer have been found that apparently originated from the Michigan infestation and were shipped out of state before the borer was discovered. It is thought that the borer has been in Michigan for 8 to 10 years. Thus, it was probably increasing its range for 6 to 8 years before it was discovered.

Regulated articles restricted under quarantine from interstate movement include the emerald ash borer; all hardwood firewood; and nursery stock, green lumber, and other material living, dead, cut, or fallen, including logs, stumps, roots, branches; and composted and uncomposted chips of the genus Fraxinus (all ash species). All hardwood species of firewood are re-stricted because as hardwood is dried and cut into firewood, it is difficult to identify the species of the tree from which the firewood was derived. Remember that mountain ash is not a true ash species, is not attacked by emerald ash borer, and is not regulated.

Where emerald ash borer is found, quarantine is set up similar to the federal quarantine cited above. Infested trees are removed, as well as all ashes near them. In Ohio infestations, all ash trees have been removed in a 1/2-mile radius around infested trees. In the Windsor, Ontario, Canada, area, an ash-free zone 5 to 6 miles wide has been established across the peninsula to stop borer movement inland. The difference in the ash-free areas is based partly on evolving research. It was initially thought that emerald ash borer adults would fly only about 1/4 mile to a new host. Very recent research has found that they can fly at least 5 miles; however, it is unclear how often that will occur. Research studies are ongoing on this and many other aspects of the emerald ash borer.

Several insecticides to control this insect have been found through research primarily conducted by Michigan State University. Because the adults are out for only a few weeks (instead of the several monthsí duration that occurs with Asian longhorned beetle flight), foliar and bark sprays are effective, as well as injected insecticides. This makes it likely that if emerald ash borer is found in Illinois, a combination of quarantine, tree removal, and insecticide application would be used in and around infested areas.

If you see emerald ash borer or its damage, contact your local University of Illinois Extension office or the Illinois Department of Agriculture at (800)641-3934.

Author: Charles Helm Phil Nixon James E. Appleby


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