Colorado Emerald Ash Borer



  • Canopy of the tree begins to thin and eventually die off
  • D shaped exit hole

Emerald ash borer is an invasive insect that originally came from Asia and was first discovered in Michigan and Windsor Ontario. This insect is green in color and are around 1/4″-1/3″ in size. Emerald ash borer has one generation per year. The female will deposit the eggs in the inner crevasses of the bark of an ash tree and can lay between 40-70 eggs. When the eggs hatch they juveniles chew through the bark and enter the cambium, phloem and xylem layers of the tree. As they feed on the cambium of the tree they will develop and increase in size to about 1″-1 1/4″ in length. In the fall the mature 4th instars create a chamber where they develop over winter into an adult by spring. As the adults chew their way out of the tree through the bark in spring the beetle leaves its characteristic D-shaped exit hole. EAB will attack both healthy and weak trees. A trademark d shaped exit hole in the trunk and branches can be found, often high in the infested tree. The EAB larvae feed in the cambium of the tree and eventually girdle the tree. The trees that are at greatest risk in Colorado are the green ash and white ash. About 20 percent of all trees in the Denver metro area are Ash trees and will need to either be treated with systemic insecticides or be cut down and removed as this invasive insect grows in population. EAB will attack both large and small ash trees but effective control has been established using Safari, imidacloprid, and emamectin benzoate. All three are systemic insecticides and are applied either as a basal trunk spray, soil injection or trunk injection.