Now, instead of automatically spraying when an insect is spotted, most gardeners stop to ask if the pest is causing enough damage to warrant control. Some insects cause cosmetic injury only, leaving the plant's health intact. In this case, some gardeners are deciding they can live with the injury. The cone-like structures formed on Colorado blue spruce by the Cooley spruce gall adelgid is one such example. Whether the introduction of pesticides into the environment is worth the time and the possibility of killing non-target insects also is of concern.
Few chemicals are selective enough to only kill the problem pest.
That leaves gardeners to weigh the benefits of spraying against the possible destruction of beneficial insects and other possible environmental impacts. Perceptive gardeners consider the plant's age when it is attacked. Cabbage can tolerate a heavier infestation of cabbageworms and tomatoes can handle an onslaught of flea beetles when these plants begin to mature. An attack during earlier stages of development can severely injure or kill plants. Some potent poisons occur in nature, and any insecticide must have some degree of toxicity to kill insects.