• Donald C. Booth, Ph. D., Entomologist

Emerald Ash Borer

Emerald ash borer (Agrilus planipennis) was first discovered in southeastern Michigan in 2002 and

has been since identified in eleven (11) adjacent states including IN, OH, IL MN, PA MD, WI, KY, MO, NY and WV. This beetle has also been found in Windsor, Canada. This borer probably has been established in the Michigan area since the late 1980’s. Emerald ash borer larvae feed in the outer sapwood of ash trees and can rapidly girdle stems and branches. Trees often die within one-to-three years following the initial attacks.

Emerald ash borer is native to Asia including China, Japan, Russia and Korea. The pest was probably introduced on pallets or wood that was used to stabilize heavy cargo. The insect affects all ash species native to the Midwest and is known to infest certain elms and walnuts within its native range in Asia.

Identification: Emerald ash borer has a similar appearance and life cycle to native Agrilus borers such as the bronze birch borer and the two lined chestnut borer that infests oak and beech. Adult beetles are emerald green and approximately ½ inch long. Larvae are segmented flat worms that can reach 1 inch in length.

Biology: Adults emerge from infested wood in

June and early July and feed on leaves of ash where they create notches in the margins. Adults mate and females lay up to 90 eggs in the bark crevices in stems and branches. Eggs hatch within 10 days and first instar larvae bores through the bark into the sapwood.

The entrance holes are inconspicuous but there is often woodpecker activity in the vicinity of new infestations. Larvae create “S” shaped feeding galleries that wind through the cambial area of the branches and stems. The galleries are packed with sawdust-like frass. Larvae complete development in the fall and overwinter as pre-pupae in chambers

in the sapwood. Pupation occurs in early spring and adults emerge in late spring through early summer. Adults leave “D” shaped emergence holes that are visible in bark of infested stems and branches. One generation occurs each year. Adults are capable of flying at least a half mile from the point of emergence. In Ohio, infestations are expanding at approximately ¼ mile per year. Long distance movement of Emerald ash borer has been attributed to transport of infested firewood and nursery stock.


Monitor ashes and other trees for symptoms of borer attacks and tree decline. The treatments available to manage the emerald ash borer are recommended on a preventative basis, before a tree has been damaged. The most effective treatment is a soil applied systemic insecticide containing the active ingredient imidacloprid.

This treatment should be soil injected for root absorption and translocation to the branches before attack. Larvae that bore into the xylem are controlled by the systemic insecticide. Late summer and fall treatments are effective, although soil applications are effective whenever soil conditions are favorable for root uptake. Treatments are less effective on trees that are already infested with borers. Larval galleries often interfere with translocation and distribution of systemic insecticide.

Although preventative treatments are generally recommended, research has indicated that soil applied imidacloprid can save ashes after they have been attacked. The condition of each tree should evaluated by a certified Arborist prior to treatment. There are several spray treatments (Permethrin & Bifenthrin) that are also effective in preventing attacks when applied to ashes. Spray treatments should be applied to stems, branches, and foliage in early June. Thorough coverage of foliage and all bark surfaces is crucial to preventing attacks. Imidacloprid can also be injected directly into the stems of ash trees to prevent colonization and control larvae already in stems and branches.

Root collar injection does not provide the residual activity that soil treatments provide, and distribution of the chemical in the crown may not be as thorough. Removal and destruction by chipping, burial, or burning is recommended for all heavily damaged ashes. Wood should not be stored as firewood through the winter months and firewood should not be transported from areas known to be infested by emerald ash borer. Maintain the health of ash trees with good cultural practices including pruning, fertilization, proper mulching and irrigation during dry periods. This will reduce stress and improve the tolerance of trees to borer attacks.