If emerald ash borer (also known as emerald green ash borer) is within five miles of your home and you have an ash tree, this pest will almost certainly invade and kill your tree. This 1/2-inch-long metallic green beetle bores into the bark of an ash, creating D-shaped entry and exit holes. Its invasion causes defoliation, wilting, splitting of the bark and eventual death. Knowledge of how to assess the tree and which control methods work will help you save the ash.
Assess your ash tree. If the canopy shows more than 40 percent dieback, you cannot save it. If the amount of dieback falls in the 20- to 40-percent range, the outcome is uncertain. If the ash shows little or no sign of infestation, you can most likely save it.
Purchase an insecticide with Imidacloprid as the main ingredient. Only a limited number of insecticides with this ingredient are available for homeowners, namely Bayer Advanced Control for Tree and Shrub Care and its generic counterparts.
Mix the insecticide with water in a bucket, according to the directions on the package, in May or early June. Drench the soil right around the base of the ash tree with the insecticide.
Drench the soil once a year, every year, to keep the tree protected. In young trees, evidence of infection should disappear in a year. Damage in older trees may take two years or more to reverse.