That depends on what you are treating. Some tree diseases, for instance, are only stopped by preventive treatments; treatments must be applied before the disease has affected your tree. For example, trees and shrubs that are prone to certain fungal leaf diseases are preventively treated three times a year with a bio-organic fungicide, usually in late spring and early summer. Once the disease is visible, it’s too late to treat it. Other treatments are applied only when the problem, whether it’s a pest or disease, is present. For example, we treat for Spotted Lanternfly when the adults are active and feeding on the leaves and sapwood.