Implants and injections should be at the base of the tree, not into the roots or above the roots. If the holes have not closed after one year, additional injections should not be done. Under no circumstances should an arborist drill a large hole into the center of a tree and insert a pipe into which pesticides will be poured. This method is totally ineffective, expensive, and causes serious, irreparable damage to your tree. Pests that do not cause serious damage, such as aphids, tent caterpillars, or anthracnose disease usually do not justify the use of injections or implants.
Most trees can withstand severe defoliation for at least one year without permanent damage.
Leaf distortion caused by insects such as aphids or leafrollers is usually not damaging to trees and shrubs because the all-important process of photosynthesis can still occur. Pests that are serious enough to warrant the use of this method include borers, bark beetles, certain spider mite species, and diseases such as cankers, fire blight, or verticillium wilt. Injections for these pests are sometimes successful, sometimes not. Some success has also been seen using the method for preventing contraction of fatal Dutch elm disease in American elms if the trees are still disease-free and are treated regularly. Injections for infestations of pests which do not normally cause permanent damage or death, such as elm leaf beetle, can be justified in years when populations are high enough to be particularly bothersome.