Factors Affecting Efficacy of Trunk-Injected Emamectin Benzoate to Manage Emerald Ash Borer
Clifford Sadof, Scott Gula, Lindsey Purcell, and Matthew Ginzel
Abstract: Background: Emerald ash borer (EAB), Agrilus planipennis, is an invasive wood-boring beetle that threatens ash trees (Fraxinus spp.) in the urban forest. Methods: We compared the efficacy at which 3 different injection systems deliver emamectin benzoate (EB) to the leaf canopy and protect trees. Two of the systems, Arborjet Tree I.V.™ and Rainbow Ecoscience Q-Connect™, used sixteen ports/m of trunk circumference, whereas the third system, Brandt enTREE® EB, used eight. Results: The two systems with more injection ports provided more uniform delivery of insecticide to the leaf canopy. Although all 3 injection systems provided excellent control for the first 2 years, only the 16-port injection systems provided protection for up to 3 years. The number of injection ports affected insecticide delivery because the sectorial structure of the ash vascular system limited lateral product diffusion. Additionally, over the course of an 8-year study, we found trunk injections of EB made in the spring provided better control of EAB than fall injections. Protection afforded by a 2013 application in our study failed by 2016 as EAB populations reached their peak. A second application in 2016 extended protection past the peak of EAB abundance through 2019. Conclusions: We conclude that when the same dose of EB is delivered, efficacy of the application is influenced by the number of injection ports used in the injection system, time of application, and the status of the local EAB population. Arborists need to be aware of these factors when planning their EAB management program.
Keywords: Agrilus planipennis; Control Persistence; Fraxinus americana; Invasive Species; Large Trees.