334 application (e.g., close to water, poor access for equip- ment, incompatible with management objectives), there are no effective alternatives yet identified. Verbenone is an anti-aggregation pheromone derived from α-pinene and used to deter beetles from attack- ing trees (Fettig et al. 2009). Green leaf volatiles (GLVs) are organic compounds (including alcohols, esters, and aldehydes) that are released when plants are wounded; these reduce bark beetle attraction to trees and are sometimes used in conjunction with verben- one as a combined strategy to protect trees (Gillette et al. 2014). Development of semiochemical treatments continues to be an active area of research, but consis- tency in effective tree protection has yet to be realized (Progar 2005; Kegley and Gibson 2009). TREE-äge® (Syngenta Crop Protection, Greens- boro, NC, USA) is a formulation of emamectin ben- zoate (EB, 4% [wt/wt]) designed for systemic application against tree pests. Formulations of EB have been shown to inhibit propagation of the pine wilt nematode, Bursaphelenchus xylophilus (Steiner and Buher) Nickle, in pine shoot tissues (Takai et al. 2003) and impact a variety of insect pests, most nota- bly Coleoptera and Lepidoptera that attack crown tis- sues, including leaves and cones (Grosman et al. 2002; Grosman and Upton 2006). The product is effective (for achieving management objectives) against the emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)(Smitley et al. 2010; McCullough et al. 2011); however, treatments applied to protect trees from bark beetles have pro- duced mixed results. Previous applications against D. ponderosae have been ineffective, as have those against D. rufipennis (Grosman et al. 2010). However, effec- tive results have been attained against D. brevicomis and in one year against D. frontalis (Grosman et al. 2009, 2010). To be useful, tree protective treatments must suc- ceed against beetle pressures that are equal to or greater than those that trigger management interventions. Beetle pressures are characterized experimentally by the observed mortality of control trees in the experi- mental population; evaluation under sufficient beetle pressure is critical for determining treatment utility and cost-to-benefit considerations. Previous studies with bark beetles and TREE-äge have predominantly lacked sufficient pest pressures to determine efficacy via the Shea protocols; however, outbreak populations of MPB in the Warner Mountains area of northeastern ©2020 International Society of Arboriculture Doccola et al: Emamectin Benzoate Efficacy Against Bark Beetles California during the late 2000s provided an opportu- nity to develop and evaluate tree protection treat- ments under conditions of heavy MPB pressure. The objectives of this experiment were: (1) to evaluate TREE-äge for its efficacy to protect trees against high levels of pressure from the mountain pine beetle in western white pine; (2) to determine EB residues in the phloem; and (3) to evaluate and improve upon existing tree-injection protocols. Three distinct field studies were installed in 2007, 2009, and 2013. MATERIALS AND METHODS This study was conducted from fall 2007 to fall 2015 in the Warner Mountains Ranger District, Modoc National Forest, California, USA. Our study site included stands that were mixed coniferous forests, predominantly lodgepole pine (Pinus contorta Dougl. ex Loud. variety murrayana) with western white pine (SAF Cover Type 218). Surveys first noted increased tree mortality from D. ponderosae in 2005, appar- ently peaking in 2008 (USDA Forest Service 2008). During the study period, over 60% of the pine com- ponent in the area was killed by MPB. The study con- sisted of three experiments; experiment 1 began with tree injections in fall 2007, experiment 2 in fall 2009, and experiment 3 in spring 2013. In each experiment, trees were selected in transects along roads, far enough to avoid the creation of road hazards from dead trees, but close enough for servicing. Trees were at least 100 m apart, each being considered an inde- pendent, experimental unit. The population of exper- imental trees consisted of 10 trees per treatment in a completely randomized design. Experiment 1 Experiment 1 evaluated prophylactic bole-injection with TREE-äge for its ability to protect western white pines from MPB-caused tree mortality. On 17 to 18 September 2007, 10 trees were injected with TREE- äge using the Tree I.V. system (Arborjet, Inc., Woburn, MA, USA), and 10 trees were set aside as untreated controls. Trees averaged 30.9 ± 2.0 cm (mean ± 1 SD) diameter at breast height (DBH), and treated trees were injected with the high label rate of 10 mL of product per 2.5 cm DBH. The Tree I.V. is a micro-infusion delivery system comprised of a 1-L pressure bottle configured with a delivery line which splits into 4 injector tips via an in-line manifold. TREE-äge was mixed 1:1 v/v with bottled, distilled
September 2020
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