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Emerald Ash Borer

June 29, 2005

Although it is not here—yet—it is important to be aware of (and on the lookout for) of the emerald ash borer, Agrilus planipennis, an exotic pest first discovered in North America in 2002 in Michigan and Ontario, Canada. A native of China, Japan, Korea, and Mongolia, the emerald ash borer is suspected to have entered on infested crates, pallets, or dunnage. The insect is presently in Michigan, Ohio, Indiana, and Canada. Emerald ash borer attacks ash trees, including green, white, blue, and black ash. Green ash is the most preferred species. The beetle has killed an estimated 8 to 10 million ash trees in Michigan, and about 40,000 trees have been removed since the infestation started. Emerald ash borer is in the same family (Buprestidae) and genus (Agrilus) as the bronze birch borer (Agrilus anxius) and the two-lined chestnut borer (Agrilus bilineatus).

Emerald ash borer adults are slender, elongate beetles about 1/2-inch long. They are metallic, and coppery-green in color. Adults are primarily active from late May through mid-August, with peak activity in mid-June. The adult emergence, or exit, holes are 1/8- to 1/6-inch wide and “D-shaped,” just like exit holes of the bronze birch borer. Adult activity is dependent on weather conditions, as adults tend to rest on tree surfaces during rainy or cloudy weather. Adults may live from 3 to 6 weeks, feeding on small quantities of plant leaves. They tend to colonize the upper area of large trees and will attack trees with 1/2-inch calipers or higher. Adults are very “good” fliers and can disperse 1/2 to 4 miles in 24 hours. Adult females can lay 50 to 90 eggs, although the range can be anywhere from 2 to 258 eggs, based on laboratory studies. Eggs are laid individually on the bark surface or just under the bark, inside cracks and crevices of trees, from June through July. After 1 week, eggs hatch into larvae that are white, flat, and 1/2 to 3/4 inch in length. The larvae eventually bore through the bark and start feeding.

Fully grown larvae, which are about 1 to 1-1/4 inch long, possess small pincer-like appendages on the last abdominal segment. They feed in the cambial region of the trunk or branches, including the phloem and sapwood region, from June through October. They create “S” or serpentine-shaped galleries that are packed with frass. The extensive galleries created by the larvae under the bark disrupt translocation of water and nutrients in the infested tree. Damage by the larvae occurs from August through October, when plants are most likely to be stressed by heat and lack of moisture. Epicormic shoots (water sprouts) will sprout from the main trunk of declining trees. Small vertical splits in the bark are a typical symptom of trees infested with larvae. The emerald ash borer overwinters as a full-grown larva in the outer bark or the outer inch of sapwood. Pupation occurs in the spring. The emerald ash borer has a 1-year life cycle in Michigan, but there are indications that it may have a 2-year life cycle. However, this is still being evaluated. Infested trees are typically killed within 1 to 3 years, depending on the density of larvae present. Although emerald ash borer tends to feed primarily on ash trees, it will also feed on walnut (Juglans sp.) and elm (Ulmus sp.).

The emerald ash borer is difficult to monitor because the adult females do not produce long-range pheromones. The monitoring technique used in Michigan involves girdling green ash trees and coating the tree with about a 1-foot band of sticky tanglefoot. Emerald ash borer is primarily spread by the movement of infested firewood; Michigan has instigated fines of $4,000 against anyone found transporting ash tree firewood out of the quarantine zone. At present, there is no insecticide program that is effective for eradication.

For homeowners, application by trunk injection of systemic insecticides such as imidacloprid from late May to early June has been suggested. However, treatments are needed each year. And if a tree is infested with larvae and numerous galleries encircle the tree, the galleries may block the movement of the insecticide active ingredient from the reaching the points beyond the galleries, which means that applications have to be initiated before the tree is infested. An early indication that emerald ash borer larvae are present is heavy woodpecker damage to trees as woodpeckers feed on the larvae.

The key to minimizing problems with the emerald ash borer, or any invasive insect species, significantly impacting the ecology of landscapes is to plant a diversity of tree species. It is important to avoid monoculture (single species) plantings. I think we should know this by now after the experience with Dutch elm disease.

You are probably wondering what Illinois is doing to prepare for the eventual arrival of the emerald ash borer. A group of individuals from the Morton Arboretum, the University of Illinois, and other agencies and organizations are working to be ready. An “Emerald Ash Borer Readiness Plan” has been created and is available at http://www.agr.state.il.us/Environment/Pest/emeraldashborer.pdf. The primary action being taken currently is to survey existing ash trees to detect any early indications. If you suspect that you have the emerald ash borer, contact your county extension office or the Illinois Department of Agriculture (IDOA).

Numerous Websites, including the three listed here, provide information and pictures that professionals and homeowners can access to determine if they have emerald ash borer: