Arboriculture & Urban Forestry 42(6): November 2016 Arboriculture & Urban Forestry 2016. 42(6): 389–399 389 Evaluation of Xylem Discoloration in Ash Trees Associated with Macroinjections of a Systemic Insecticide Sara R. Tanis and Deborah G. McCullough Abstract. Emerald ash borer (EAB) (Agrilus planipennis), first identified near Detroit, Michigan, U.S., in 2002, has killed millions of ash trees (Fraxinus spp.) in 28 states and two Canadian provinces to date. Trunk injections of insecticide products containing ema- mectin benzoate (EB) (e.g., TREE-äge®) are oſten used to protect ash trees in landscapes from EAB, but wounds and potential injury resulting from injections are a concern. Researchers examined 507 injection sites on 61 trees and recorded evidence of secondary wounding (e.g., external bark cracks, internal xylem necrosis and pathogen infection). Researchers assessed 233 injection sites on 22 green ash and 24 white ash trees macro-injected with a low or a medium-high rate of EB in 2008 only, or in both 2008 and 2009. Only 12 of 233 injection sites (5%) were associated with external bark cracks and there was no evidence of pathogen infection. On 39 of the 46 trees (85%), new xylem was growing over injection sites. Researchers assessed 274 injection sites on 15 green ash trees injected annually with EB from 2008 to 2013 or injected in 2008 and again in 2011. Bark cracks were associated with four injection sites on three trees, but no evidence of injury was found on the other 12 trees. All 15 trees had new xylem laid over injection sites. Confocal laser scanning and polarizing digital microscopy were used to assess the integrity of discolored xylem tissue removed from the immediate area surrounding 140 injection sites on 61 trees. Researchers found no evidence of decay associated with discoloration. Key Words. Agrilus planipennis; Bark Cracks; Emamectin Benzoate; Fraxinus americana; Fraxinus pennsylvanica; Green Ash; Insecti- cide; Macroinjection; Trunk Injection; White Ash. Emerald ash borer (EAB), (Agrilus planipennis) (Coleoptera: Buprestidae), a phloem-feeding insect native to Asia, has killed hundreds of millions of native ash (Fraxinus spp.) trees in landscapes and forests since it was identified in southeast Michigan, U.S., and Windsor, Ontario, Canada, in 2002 (Cappaert et al. 2005). To date, popula- tions of EAB have been found in at least 28 states and two Canadian provinces (EAB Information Network 2016). Economic costs associated with removing dead or dying landscape ash trees in urban and suburban landscapes can overwhelm municipal forestry budgets, as well as homeown- ers (Kovacs et al. 2010; McCullough and Mercader 2012; Kovacs et al. 2014). Soon aſter this invasive pest was identified, researchers began evaluating systemic insecticide options to protect valuable landscape ash trees. Control efforts typically target adult beetles, who feed on ash leaves throughout their 3–6-week life span, and larvae, which feed on phloem and cambium in serpentine galleries that generally score the outer sapwood (Cap- paert et al. 2005; Herms and McCullough 2014). Several systemic insecticides are now available in the U.S. to protect landscape ash trees from EAB (Herms and McCullough 2014; Herms et al. 2014; McKenzie et al. 2010). Although some products can be applied as soil drenches or as a basal trunk spray, most systemic products can be directly injected into the base of the trunk, elimi- nating insecticide driſt and minimizing applicator exposure, as well as non-target or environmental effects (Sur and Stork 2003; Sanchez-Zamora and Fernandez-Escobar 2004; Hahn et al. 2011; Herms et al. 2014). Systemic insecticides are translocated in xylem tissue up the trunk to canopy branches and leaves (Choat et al. 2007; Mota-Sanchez et al. 2009; Tanis et al. 2012). Ash trees are ring porous (Dickison 2000), and all, or nearly all, insecticide translocation occurs in the outer rings of sapwood. ©2016 International Society of Arboriculture
November 2016
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