Arboriculture & Urban Forestry 33(1): January 2007 19 desirable because of the increased number of wounds that result. The Tree I.V., on the other hand, has a 500 mL (15 fl oz) liquid capacity; therefore, it is not limited to the micro- injection capsule dosage or necessarily to the same frequency of application. The sensitivity of hemlock to HWA requires a high level of control as that observed after a second applica- tion of imidacloprid. In this study, the level of efficacy re- quired and subsequent duration was achieved after a 1 × dose rate × 2 treatments. It is our premise that a 2 × dose rate × 1 treatment is preferable when treating by tree injection. A lower number of injection wounds will be an added benefit of less frequent applications. The increased volume trunk injec- tion is what we term Micro-infusion. CONCLUSIONS It was our observation that left untreated, HWA on hemlock reached levels that negatively affected tree health. In the 3 years of the study, winter low temperatures were insufficient to cause an appreciable or sustainable reduction in infestation levels (highest mortality in the controls was 53.3%). Total HWA pressure actually increased significantly (to 4.91/linear cm) in the controls by year 3. Treatment with stem-injected imidacloprid did not provide a quick knockdown of theHWA population; rather, our observation was that it required time (i.e., at least 1 year). In the year after treatment, we observed significantly greater HWA mortality in the IMA-jet trees (91.4.0%). However, we did not observe sufficient control of HWA for trees to recover until 1 year after the second treat- ment. We think that it is preferable to use 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 g A.I./cm dbh) for this level of efficacy to limit the number of wounds a tree receives to centimeter dbh/5 and to extend the injection interval (to once every 2 years). This recommendation, however, does not pre- clude the arborist from using generally recognized Integrated Pest Management practices (I.P.M.). The practitioner should monitor insect mortality and tree health annually. It is pref- erable to do so in the fall to plan the subsequent year’s treat- ments. It is our intent that this article helps to inform that process. Wound response to the Tree I.V. and VIPER injec- tion method is currently being studied. The new rate recom- mendations 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. LITERATURE CITED Baker, N.R., K. Oxborough, T. Lawson, and J.I.L. Morison. 2001. High resolution imaging of photosynthetic activities of tissues, cells and chloroplasts in leaves. Journal of Ex- perimental Botany, Oxford University Press 52:615–621. Brodribb, T.J., and T.S. Felid. 2000. Stem Hydraulic supply linked to leaf photosynthetic capacity: Evidence from New Caledonian and Tasmanian rainforests. Plant, Cell & Environment 23:1381. Costa, S.C., M. Skinner, and B.L. Parker. 2004. HWA cold- hardiness: Towards defining limits of range expansion. Proceedings, XV USDA Interagency research Forum on Gypsy Moth and Other Invasive Species. GTR-NE-332. 19–22. Doccola, J.J., P. Castillo, and C. Taylor. 2002. Hemlock health and Hemlock woolly adelgid management in the urban forest. In proceedings, Hemlock woolly adelgid in Eastern United States Symposium. Feb. 2002. Rutgers University and New Jersey Agricultural Experiment Sta- tion in cooperation with the USDA Forest Service. Doccola, J.J., P.M. Wild, I. Ramasamy, P. Castillo, and C. Taylor. 2003. Efficacy of Arborjet Viper microinjections in the management of hemlock woolly adelgid. Journal of Arboriculture 29:327–330. Dujesiefken, D., W. Liese, W. Shortle, and R. Minocha. 2005. Response of beech and oak to wounds made at different times of the year. European Journal of Forest Research 124:113–117. Grosman, D.M., W.W. Upton, F.A. McCook, and R.F. Bill- ings. 2002. Systemic insecticide injections for control of cone and seed insects in Loblolly pine seed orchards—2 year results. Southern Journal of Applied Forestry 26: 146–152. Hudler, G.W., and S. Jensen-Tracy. 2002. Lac balsam as a treatment to hasten wound closure and minimize discol- oration and decay. Journal of Arboriculture 28:264–269. Jenkins, J.J. 1994. Use of imidacloprid for aphid control on apples in Oregon: Potential for ground and surface water contamination. Department of Agricultural Chemistry. Oregon State University, Corvallis, OR. Kozlowski, T.T., and C.H. Winget. 1963. Patterns of water movement in forest trees. Botanical Gazette 124:301–311. Lancashire, J.R., and A.R. Ennos. 2002. Modeling the hydro- dynamic resistance of bordered pits. Journal of Experi- mental Botany 53:1485–1493. Larson, D.W., J. Doubt, and V. Mattes-Sears. 1994. Radially sectored hydraulic pathways in the xylem of Thuja occi- dentalis as revealed by the use of dyes. International Jour- nal of Plant Sciences 155:569–582. Martin, J.M., and T.D. Sydnor. 1987. Differences in wound closure rates in 12 tree species. HortScience 22:442–444. Mayr, S., B. Rothart, and B. Damon. 2003. Hydraulic effi- ciency and safety of leader shoots and twigs in Norway spruce growing at the alpine timberline. Journal of Ex- perimental Botany 54:2563–2568. McClure, M.S. 1991. Density-dependent feedback and popu- lation cycles in Adelges tsugae (Homoptera: Adelgidae) on Tsuga canadensis. Environmental Entomology 20: 258–264. ©2007 International Society of Arboriculture
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