The emerald ash borer is an invasive insect that can attack and kill a healthy ash tree if an effective treatment is not started as soon as you see the first signs of disease, which will be a deteriorating canopy. If more than 50 percent of the canopy is gone, it would be too late to save the tree. At the first sign of the emerald ash borer destruction and deteriorating canopy, you can begin a treatment to stop the disease and help the tree back to health, but it can take time and money.
Use an insecticide that is applied to the soil in mid-fall or late spring. Use a product that has the active ingredient is imidacloprid, which can kill the emerald ash borer.
Rake away all mulch, leaves and other debris from the base of the ash tree. The insecticide solution must be applied to the soil and not over any debris, which will prevent the solution from soaking into the soil.
Mix the insecticide according to the instructions on the package. It is very important that you mix the correct amount for the diameter of the tree base. Use a tape measure to find the diameter of the tree.
Use goggles and gloves when applying the solution to the soil. Slowly pour the solution around the base of the tree. Soak the soil very well. You should add enough mixture to each area around the tree so that the wetness reaches down at least an inch or two inches into the soil.
Repeat the treatment the next year.