That depends. Many of the most effective insect and disease treatments can only be applied by professionally licensed pesticide applicators. While there are some options available to homeowners to treat 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. We've also seen many cases of homeowners misdiagnosing the problem and applying toxic treatments that don't have any positive effect. Large or tall trees are very difficult to treat effectively without specialized equipment, such as a high-powered spray rig to reach the upper parts of the tree or a tree injection kit for systemic pesticides. In general, we recommend having larger trees treated by a professional with the knowledge and equipment to do the job correctly.