Many types of insects harm trees, eating leaves or depriving the tree of water and nutrients. Insecticides offer one solution when faced with an insect problem on your tree. However, other methods offer better safety and equally good results, making the insecticide treatment of trees a matter of consideration for gardeners.
To many insects, trees act as a large, stationary food source, so not surprisingly, many different types of insects harm trees. Insects, like aphids and plant bugs, suck sap from leaves and stems, caterpillars devour leaves and wood borers drill holes into trees. Approved pesticides for use by the home gardener vary from state to state, and the U.S. Environmental Protection Agency occasionally removes pesticides from the market. Consult an extension office or nursery to find the best pesticide for your insect problem.
Insecticides offer a tempting ease of use for controlling insects that are harming your tree. However, according to the University of California Statewide Integrated Pest Management Program, gardeners often misuse pesticides by trying to treat problems unrelated to insects or in situations where non-pesticide treatments would be equally effective.
Insecticide application involves gathering knowledge about the pest and using that knowledge to make the safest and most effective insecticide choices. According to the University of Minnesota Extension, you should learn about the life cycle of the insect pest, when insecticides are most effective and when to expect insects to enter that phase in your area. Whenever possible, choose insecticides that will not harm beneficial insects and minimize damage to plant and other wildlife.
Pesticides are deadly. As the University of Minnesota Extension points out, they often kill insects other than the target pest. Some of these insects--such as ladybugs and parasitic wasps--may be natural enemies of the insects you're trying to eliminate. When spraying insecticides, be mindful of drift caused by wind that could expose you or others to pesticides. Target the specific pest, and don't forget the bark or undersides of leaves, if pests are found there.
The push towards sustainable agriculture has led to the development of insecticides that capitalize on processes that protect plants in nature and, as a result, are safer to use. The Iowa State University Extension recommends botanical insecticides, which are derived from plant chemicals that naturally kill pests. Bacillus thuringiensis, or Bt, is a bacteria that infects insects, paralyzing their digestive tracts, ceasing feeding and eventually killing them. Colorado State University Extension recommends Bt for caterpillars that feed on tree leaves and needles, pointing out that the specificity of the pesticide prevents harm to organisms other than the intended pests.