Practice the concept of integrated pest management (IPM). The steps are: identify the pest(s), attempt to prevent the pest issue, monitor the populations and damage, determine a threshold, use control methods (nonchemical and chemical), and assess the performance of control tactics.
When pesticide use is necessary, remember: THE LABEL IS THE LAW! Read the label thoroughly and follow the instructions carefully. Use only the amount recommended; do not overapply or underapply! Underapplying a pesticide can cause just as much resistance as overapplying. Underapplying a pesticide does not control your pest and puts chemicals into the environment unnecessarily.
If chemical control is needed more than once in a growing season, vary the type of chemical you use. For example, let’s say that your pepper plants become infested with whitefly. Other control methods have failed and you need to apply a pesticide. The pesticide is effective, but then several weeks later, the problem recurs. If chemical control is necessary again, use a pesticide that has a different active ingredient than the first one selected. Varying the type of pesticide used can help keep pests from developing resistance.
Introduction to Pesticide Resistance -- Pesticide Environmental Stewardship