Insects damage trees and shrubs in many ways, cutting into bark and branches, defoliating leaves and transmitting disease. Infestations range from merely unsightly to deadly to your plant. Control of insect infestations takes several forms as well, with the University of Minnesota Extension recommending non-chemical solutions whenever possible. In extreme cases, however, pesticide use may be the best choice to save the plant.
Before putting any treatment plan into place, it is essential to correctly identify the insect pest, according to the University of Minnesota Extension, and learn about its life cycle. Knowledge of the pest you're dealing with helps you to make informed choices and avoid squandering money and efforts on ineffective treatments. For example, insecticide treatments against adult scale are largely ineffective and should be applied when the insects are in the larval stage.
Healthy plants better resist insect damage, so keeping your trees and shrubs properly watered and maintaining healthy, fertile soil are strong first steps. Some infestations caught early on younger plants can be removed by hand, such as bagworms or early signs of scale insects. Keep the area around plants free from weeds and clean up branches, leaves and other plant debris that may shelter damaging insects. Inspect your plants often to catch infestations before they become serious and require more drastic treatment measures.
When infestation becomes severe or highly damaging, pesticide application sometimes becomes warranted. Only select pesticides that are approved for the insect you want to eradicate and the plant you are treating. Always follow all instructions on the label carefully, and do not over-apply or under-apply. According to the University of Florida IFAS Extension, improper use most often causes insecticides to not work, not a failure of the product itself.
Bacillus thuringiensis, or Bt for short, is the only approved microbial insecticide available. Bt infections occur naturally in insects, paralyzing their digestive tracts and eventually killing them. Many insects damaging to trees and shrubs are susceptible to Bt, including the tent caterpillar, fall webworm and leaf roller. Bt insecticides are formulated to target a specific pest, so they do not harm beneficial insects the way that traditional insecticides may. Bt is also nontoxic to people, pets and wildlife.
"Pesticides are designed to be toxic to living things; so, by their very nature, they pose risks," writes entomology professor Keith S. Delaplane of the University of Georgia Cooperative Extension. Pesticides may be harmful to humans or to other organisms in the environment that come into contact with them. For example, broad-spectrum pesticides may kill beneficial ladybugs and wasps in addition to the pest. It is essential to follow all precautions on the label when applying a pesticide and to know the risks.