206 Smitley et al.: Protection of Ash Trees with Emamectin Benzoate Arboriculture & Urban Forestry 2010. 36(5): 206–211 Multiple-year Protection of Ash Trees from Emerald Ash Borer with a Single Trunk Injection of Emamectin Benzoate, and Single-year Protection with an Imidacloprid Basal Drench David R. Smitley, Joseph J. Doccola, and David L. Cox Abstract. Green ash (Fraxinus pennsylvanica Marsh.) street trees ranging in size from 25 to 45 cm dbh were trunk injected with emamectin benzoate at rates of 0.10–0.60 g ai/2.54 cm dbh at three Michigan, U.S., locations in 2005 or 2006. Tree health was monitored by annual canopy thinning and dieback ratings for up to four years after a single treatment. Branch samples were collected in the autumn and the bark removed to count emerald ash borer larvae for most treatments over the same period of time. A single trunk injection treatment of emamectin benzoate at the 0.1, 0.2, or 0.4 g ai rate gave 100% control of emerald ash borer larvae in 98 of 99 treated trees for 2–3 years. Canopy ratings for treated trees remained similar for 2–4 years following trunk injection, while >50% of the control trees died during the same period of time. Ash trees that received a combination of an imidacloprid trunk injection and an imidacloprid basal drench or an annual imidacloprid basal drench had similar canopy ratings, but more larvae were found in branches from trees receiving the annual basal drench. Key Words. Agrilus planipennis; Ash; Emerald Ash Borer; Emamectin Benzoate; Fraxinus; Trunk Injection. Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Co- leoptera: Buprestidae) is native to China, Korea, Taiwan, Japan, Russia, and Mongolia (Haack et al. 2002; Bray et al. 2007). It was first discovered in North America in 2002 after urban ash trees near Detroit, Michigan, U.S., were observed to decline and die at an unprecedented rate (Cappaert et al. 2005; Smitley et al. 2008). As of March 2010, EAB has been found in 13 U.S. states (Michigan, Ohio, Indiana, Illinois, Pennsylvania, Kentucky, Wis- consin, West Virginia, Maryland, Virginia, Missouri, Minnesota, and New York), and two Canadian provinces (Ontario and Qué- bec) (USDA 2010). Unfortunately, EAB is causing nearly 100% mortality of ash (Fraxinus spp.) trees in any growing environ- ment unless they are treated with efficacious insecticides (Cap- paert et al. 2005; Poland and McCullough 2006; Smitley et al. 2008). As EAB continues to spread, an increasing number of municipalities and private property owners face difficult deci- sions about the removal of ash trees or investment in insecticide treatment of selected trees. Trunk injections of imidacloprid or emamectin benzoate, and basal soil applications of imidacloprid were adequately efficacious against emerald ash borer when ap- plied every year, but little information is available on more than one year of control following a single treatment (Cappaert et al. 2005; Herms et al. 2009; Smitley et al. 2010). Up until this time, very few private property owners and a small proportion of mu- nicipalities have chosen to treat ash shade trees with insecticides, most likely because they believe insecticide treatments are more expensive than tree removal, or are not reliable for saving ash trees. During the past five years, trunk injections of emamectin benzoate have dramatically changed the cost/benefit analysis for treating ash trees to protect them from EAB. Data presented in this paper detail extremely efficacious and consistent protection ©2010 International Society of Arboriculture over multiple years from a single application. This results in a lower annual cost than previous treatments, less injury to trees, and improved environmental safety because all of the insecticide is contained within the tree, with the exception of any residue that may be found in shed leaves (Kreutzweiser et al. 2008). MATERIALS AND METHODS Trunk injection of emamectin benzoate was evaluated for con- trol of EAB larvae for 2–4 years following a single treatment of green ash (Fraxinus pennsylvanica Marsh.) street trees at three locations: Troy, East Lansing, and Adrian, Michigan. Emamectin benzoate treatments were compared with a control (nontreated) treatment at each location, and also with a standard treatment (imidacloprid trunk injection plus imidacloprid basal soil drench) at the Adrian site. Efficacy against EAB larvae was determined by collecting branch samples each autumn and removing the bark to count larvae and new galleries. Branches were pruned from the upper one-third of the tree canopy between September 15 and November 4 each year. Three branches, at least 1.0 m long and with a diameter between 4 and 12 cm, were removed from each tree by city arborists using a bucket truck, while additional crew provided assistance from the ground. Branches in this size range were chosen because in previous surveys the greatest density of EAB larvae was found in branches with a diameter of 8–12 cm (Marshall et al. 2009). All of the trees in this study were healthy at the start of testing, dead branches were rarely encountered with the exception of the control trees. When the canopy thin- ning of control trees exceeded 65% in July, some branches of these trees were found to be entirely dead during branch sampling in autumn. In September and early October, dead branches were
September 2010
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