Does trunk injection with emamectin benzoate (TREE-Age) injure Fraxinus spp. (ash) trees?

Systemic insecticides applied to the soil or injected into the base of tree trunks are often used to protect valuable ash Fraxinus spp. trees from emerald ash borer, Agrilus planipennis, Fairmaire (EAB) (Coleoptera: Buprestidae) in landscapes. In a recent study, a relatively new product containing the active ingredient emamectin benzoate (EB) demonstrated high levels of efficacy against A. planipennis for at least two years. EB was applied by drilling through the outer bark and into the xylem with a 3/8” drill bit, inserting a plug, then injecting the product using the Arborjet Quickjet® system. Property owners and arborists have raised concerns about potential wounds created by the injection process. In October 2009, we felled 26 trees that were injected in 2007 and 21 trees that were injected in both 2007 and 2008 (47 total trees). We removed cross sections from the lower 0.5 m of trunks, sanded the surface and assessed the presence and extent of any wounds associated with the injection points. Discoloration caused by the insecticide was present around the injection site. Confocal laser scanning microscopy was used to determine that this discoloration was not to be harmful to trees. Our results indicate that new wood was laid down over the vast majority of injection sites and that permanent injury was rare.