Emerald ash borers are beetles that get their name because adults are a bright, metallic green. The beetles cause canopy thinning and dieback because they disrupt the tissues that conduct water and nutrients in the tree. The beetles leave characteristic “D”-shaped exit holes in the bark, approximately 1/8-inch in diameter, when they emerge in late May/June. Heavy infestations can kill a tree in a couple of years. Emerald ash borer has been found in the Midwest and east coast and has not made it to Oregon or the west coast yet.
Insecticides can be used to control emerald ash borer