A recent inquiry from an Extension and Outreach colleague about timing of preventive treatments for the emerald ash borer (EAB) was insightful. This note is written to help direct types of treatments to the seasons they are most appropriate.
Insecticide product labels state that there are two windows for preventive treatments when applied to the soil or externally to the trunk of the tree: Spring and Fall. Iowa State University Extension and Outreach publication PM2084 currently includes both windows, in keeping with the product labels. Trunk injections can be done in a wider window (May through September 1) when the tree has a full crown and there is good soil moisture.