Journal of Arboriculture 31(4): July 2005 205 branches. Because movement of injected chemicals from injection site to target is dependent on the health of the transport tissues, it is critical to treat early while HWA populations are still low (<1 HWA per linear centimeter). Furthermore, our goal was to achieve therapeutic levels of insecticide that extend protection and lengthen the injection cycle to every 2 to 3 years. Residue studies are ongoing; however, we believe higher residues will result from applying insecticides at rates higher than applied in this study. CONCLUSIONS Therapeutic trunk injection treatments using the Arborjet VIPER system resulted in HWA mortality sufficient to maintain health in trees. Eighty-seven percent of all treated samples had less than 1 live adelgid per linear centimeter. The results of this study suggest that the Arborjet VIPER system is an effective management tool for trunk injection applications in the urban environment. LITERATURE CITED 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 Station in cooperation with the USDA Forest Service. Figure 3. Histogram of treated samples (top) and control samples (bottom). sample and four outlier values in the control sample. The Student’s t-test was run without the outlier values, with the same results.) We therefore have a 90% level of confidence that the true difference between the mean live HWA density between the control and treatment populations ranges from1.26 through 1.81 live HWA per linear centimeter. DISCUSSION In this study, imidacloprid-injected trees had significantly lower HWA populations than noninjected trees. The mean percent- age of HWA mortality of injected hemlocks was 85%—over twice the mean mortality of nontreated hemlock trees. Tattar et al. (1998) also found the translocation of microinjected imidacloprid had similar effect on controlling the HWA. It has been established that as HWA density increases, shoot extension decreases (McClure 1991; Doccola et al. 2002). We suspect that in protracted infestations with high HWA density (>2.0 per linear centimeter), the reduction of vitality in hemlock branches also restricts translocation. In this study, 17% of the treated samples had HWA densities greater than 1 HWA per linear centimeter. Samples with high HWA density may have limited mortality due to reduced translocation of the systemic insecticide to those McClure, M.S. 1991. density-dependent feedback and population cycles in Adelges tsugae (Homoptera: Adelgidae) on Tsuga canadensis. Environ. Entomol. 20:258–264. McClure, M.S., S.M. Salom, and K.S. Shields. 1996. Hemlock Woolly Adelgid. Forest Health Technology Enterprise Team, USDA Forest Service, Morgantown, WV. 14 pp. Shigo, A.L. 1991. Modern Arboriculture: A Systems Approach to the Care of Trees and their Associates. Shigo and Trees, Associates, Durham, NH. Tattar, T.A., J.A. Dotson, M.S. Ruizzo, and V.B.Bruce. 1998. Translocation of imidacloprid in three tree species when trunk and soil injected. J. Arboric. 24:54–56. USDA Forest Service. 2002. Hemlock Wooly Adelgid, Northeast Area—State & Private Forestry. http:// na.fs.fed.us/fhp/hwa (accessed 6/7/05). 1*Director of Research and Development 2 Ph.D., Chief Scientist 3,4,5 Research Associate Arborjet, Inc. 70 Cross Street Winchester, MA 01890, U.S. *Corresponding author ©2005 International Society of Arboriculture
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