Tree injections are the most effective options for treating insects that feed on the tender spring shoots of a tree. According to entomologists at the University of Nebraska-Lincoln, by injecting the tree you can minimize the amount of chemical used and are unlikely to have to re-treat because of adverse weather. With injection, the tree delivers the poison only to feeding insects, thereby preserving beneficial insects that may be an important part of your tree's ecosystem.
Attach the trunk injection device to the pesticide reservoir according to the manufacturer's instructions (mixing is rarely required). In most cases this will be as simple as inserting the tube attached to the injector through the mouth of the reservoir and into the pesticide.
Pre-drill a hole if required. Follow the instructions for depth and do not exceed them. If the pesticide is injected deeper than the first tow rings of the tree, it will not be taken up by the tree's vascular system.
Insert the tip of the injector into the bark or pre-drilled hole. Slowly depress the plunger to deliver the prescribed amount of insecticide to the tree.
Apply more injections if a single hole cannot handle the full dose needed for your tree and pest problem. This is dictated by the size of your tree and the type of insecticide. Follow the manufacturer's instructions for more specific instructions. Most commonly, subsequent injections will band the trunk of the tree at regular intervals (usually every 4 to 6 inches) using the same depth and amount as the original injection.