That depends. Many of the most effective insect and disease treatments can only be applied by professionally licensed pesticide applicators. While there are homeowner treatment options for small trees, these require careful application to avoid unintended environmental impacts. For example, products can leach into groundwater and some products are highly toxic to pollinators and aquatic invertebrates. In general, we recommend having trees that are larger than 12-14 inches in diameter (as measured 4.5 feet from the ground) treated by a professional with the knowledge and equipment (such as a high-powered spray rig or tree injection kit) to do the job correctly.