12 Doccola et al.: Trunk-Injected Imidacloprid for Hemlock Woolly Adelgid Arboriculture & Urban Forestry 2007. 33(1):12–21. Efficacy and Duration of Trunk-Injected Imidacloprid in the Management of Hemlock Woolly Adelgid (Adelges tsugae) Joseph J. Doccola, Eric J. Bristol, Samantha D. Sifleet, Joseph Lojko, and Peter M. Wild Abstract. Hemlock woolly adelgid (Adelges tsugae) (HWA) is an introduced piercing, sucking insect that affects hemlocks (Tsuga spp.) by extracting carbohydrates from the xylem ray parenchyma cells. Left untreated, HWA will result in reduced shoot growth, branch dieback, and ultimately tree death. In this study, the insecticide IMA-jet (5% imidacloprid w/w) was applied by trunk microinjection with the Arborjet Tree I.V. using the VIPER method. Sixteen randomly selected HWA- infested hemlocks were treated in 2002 and 2003 and eight trees were selected as untreated controls. Eight infested branch samples per tree were cut each year (2003, 2004, and 2005) and assessed. Four parameters were used to assess the efficacy and duration of treatments. These were percent HWA mortality, total and live HWA per linear centimeter shoot growth, and current-year shoot growth. The eastern hemlock (T. canadensis) in this study had high initial HWA pressure. In the 3 years of the study, winter low temperatures were insufficient to cause an appreciable or sustainable reduction in infestation levels. In the controls, HWA increased and hemlock growth decreased. Treatment with stem-injected imidacloprid did not provide a quick knockdown of the HWA; rather, it required time (i.e., at least 1 year). In the year after a second treatment, we observed sufficiently high HWA mortality for hemlock to resume growth. We have a high degree of confidence that a repeat treatment increased the levels of imidacloprid for the duration of efficacy observed. We recommend a 2× dosage (e.g., for trees in the 30 to 59 cm [12 to 23.6 in] size class, increase from 0.08 g A.I. to 0.16 gm A.I./cm trunk diameter at breast height [dbh]) for an increased level of efficacy to extend the injection interval (to once every 2 years) and to limit the number of wounds a tree receives to centimeters dbh/5 (dbh in/2). The new rate recommendations are reflected on the IMA-jet label amended in 2006. These results demonstrate that hemlock with high HWA pressure can be successfully treated using IMA-jet and the Arborjet Tree I.V. system. Key Words. Arborplug; hemlock; hemlock woolly adelgid; IMA-jet; imidacloprid; micro-infusion; plant health; sys- temic injection; Tree I.V.; trunk injection; VIPER; wound response. Hemlock woolly adelgid (Adelges tsugae) (HWA) is an in- troduced piercing, sucking insect that negatively affects hem- locks (Tsuga canadensis, T. caroliniana) by extracting car- bohydrates from the xylem ray parenchyma cells (McClure 1991). Tree health is dependent on these carbohydrates for growth, maintenance, reproduction, defense, and storage (Shigo 1991). Eastern hemlock (T. canadensis) shows a marked sensitivity to HWA infestation. McClure (1991) has reported that as few as four HWAs/20 mm2 of branch seri- ously affected growth in forest stands. The observable changes include reduction of shoot growth (stunting), chlo- rosis (yellowing), and shedding (needle loss), all of which are symptomatic of suppressed hemlock health. Dieback in hem- lock may occur within 2 years of HWA infestation, first affecting the lower canopy and then progressing upward in the tree (McClure et al. 1996). Hemlock mortality can occur in as little as 4 years of initialHWAinfestation (McClure 1991). ©2007 International Society of Arboriculture The three treatment options recommended for managing HWA infestations are foliar sprays, soil application, and trunk injection. Spray applications of horticultural oil, insec- ticidal soap, or petrochemical insecticides are used for treat- ment ofHWAbut depend on thorough foliar coverage, which is difficult in tall trees (McClure 1998) and subject to aerial drift. Soil-injected insecticides eliminate the problem of drift inherent in foliar applications, but leaching in the soil profile is of concern in sensitive sites (Jenkins 1994; Rômulo et al. 2004). Trunk injection is an environmentally sensitive, effec- tive, and long-lasting approach to pesticide application (Gros- man et al. 2002; Potter et al. 2002; Young 2002; Shearer et al. 2004). Although effective, the wounds created when trees are in- jected are a concern to the arborist (Shigo 1977, 1979, 1984; Pearce 2000). Trees do tolerate some wounding; however, the more frequently injections are made, the more apt the con-
January 2007
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