Arboriculture & Urban Forestry 39(1): January 2013 vations found higher HWA and EHS populations on T. canadensis in these plots compared to the shaded Hemlock Hedge planting, which may also be contributing to the lower aesthetic values associated with some of these trees. The hotter, drier, sunnier conditions may stress T. canadensis predisposing them to greater injury from insect pests (Mattson and Haack 1987) or otherwise provide conditions more favorable for pest development. An alternative hypothesis is that the hemlocks surrounded and partially shaded by hardwoods may benefit from generalist predators from the surrounding arboreal vegetation (Hanks and Denno 1993). CONCLUSIONS Currently, 17 of 18 (94.4%) T. chinensis specimens have survived since their initial installation at Lasdon Park and Arboretum in Northern Westchester County on September 30, 2003. Observa- tions since establishment find a consistent growth and excellent visual quality (i.e., lush green foliage) on a tree that somewhat resembles the form and appearance of T. canadensis. T. chinensis is shade tolerant, features a relatively rapid growth rate, and is resistant to HWA (Del Tredici and Kitajima 2004; Hoover et al. 2009; Montgomery et al. 2009; Weston and Harper 2009). These established traits continue to strengthen the case that this tree would make a suitable replacement for T. canadensis in north- eastern landscapes. Along with resistance to HWA, there are some indications that it could be less susceptible to spruce spider mites (Del Tredici and Kitajima 2004) and possibly elongate hemlock scale (Weston and Harper 2009), relative to eastern hemlock. The current study suggests, should Chinese hemlock require treatment for any pest that can be managed with horticultural oil, the species tolerates a 1% or 2% horticultural oil application in the autumn. Acknowledgments. Special thanks to the Watershed Agricultural Coun- cil for providing a financial contribution towards this research, and to Lora Schwartzberg, Jason Dampier, Jessica Rennells and Jerry Giordano for their assistance associated with the collection/interpretation of field data, weather records, administration of horticultural oil and general plot maintenance. We are also grateful to Ted Kozlowski and the staff at Las- don Park and Arboretum, and the Westchester County Parks, Recreation and Conservation department for the space to conduct this research and access to on-site resources. Finally, we wish to acknowledge the ongoing support of both the Cornell University Cooperative Extension of West- chester County, and Paul A. Weston, Ph.D., for his invaluable contribu- tion in the setup and establishment of the original hemlock spp. research planting on September 30, 2003. LITERATURE CITED Baxendale, R.W., and W.T. Johnson. 1988. Evaluation of summer oil spray on amenity plants. Journal of Arboriculture 14(9):220–225. Cowles, R.S. 2009. Optimizing dosage and preventing leaching of imida- cloprid for management of hemlock woolly adelgid in forests. Forest Ecology and Management 257:1026–1033. Cowles, R.S. 2010. Optimizing a basal bark spray of dinotefuran to man- age armored scales (Hemiptera: Diaspididae) in Christmas tree plan- tations. Journal of Economic Entomology 103:1735–1743. Cowles, R.S., and C.A.S.-J. Cheah. 2002a. Systemic control of hemlock woolly adelgid, 1999. Arthropod Management Tests 27:G47. Cowles, R.S., and C.A.S.-J. Cheah. 2002b. Foliar sprays for control of hemlock woolly adelgid, 2001. Arthropod Management Tests 27:G48. 9 Cowles, R.S., M.E. Montgomery, and C.A.S.-J. Cheah. 2006. Activity and residues of imidacloprid applied to soil and tree trunks to control hemlock woolly adelgid (Hemiptera: Adelgidae) in forests. Journal of Economic Entomology 99:1258–1267. Davidson, J.A., S.A. Gill, and M.J. Raupp. 1990. Foliar and growth ef- fects of repetitive summer horticultural oil sprays on trees and shrubs under drought stress. Journal of Arboriculture 16:77–81. Del Tredici, P., and A. Kitajima. 2004. Introduction and cultivation of Chinese hemlock (Tsuga chinensis) and its resistance to hem- lock woolly adelgid (Adelges tsugae). Journal of Arboriculture 20:282–287. Hanks, L.M., and R.F. Denno. 1993. Natural enemies and plant water relations influence the distribution of an armored scale insect. Ecol- ogy 74:1081–1091. Havill, N.P., and M.E. Montgomery. 2008. The role of arboreta in study- ing the evolution of host resistance to the hemlock woolly adelgid. Arnoldia 65:2–9. Hodgkinson, M.C., D. Johnson, and G. Smith. 2002. Causes of phyto- toxicity induced by petroleum derived spray oil, pp. 170–178. In: A. Beattie, D. Watson, M. Stevens, D. Rae, and R. Spooner-Hart (Eds.). Spray Oils Beyond 2000, Sustainable Pest and Disease Management. Univ. Western Sydney. 627 pp. Hoover, B.K., R.M. Bates, J.C. Sellmer, and G.A. Hoover. 2009. Chal- lenging Chinese hemlock (Tsuga chinensis) with hemlock woolly adelgid (Adelges tsugae) ovisacs. Arboriculture & Urban Forestry 35(1):1–4. Johnson, W.T., and H.H. Lyon. 1994. Insects That Feed on Trees and Shrubs. 2nd Ed. Rev. Cornell University Press, Ithaca, New York, U.S. Mattson, W.J., and R.A. Haack. 1987. The role of drought in outbreaks of plant-feeding insects. Bio-Science 37(2):110–118. McClure, M.S. 2002. Elongate Hemlock Scale. USDA Forest Service Pest Alert. Acessed 03/22/2011. McClure, M.S., and M.B. Fergione. 1977. Fiorinia externa and Tsugas- pidiotus tsugae (Homoptera: Diaspididae): Distribution, abundance, and new hosts of two destructive scale insects of eastern hemlock in Connecticut. Environmental Entomology 6:807–811. Montgomery, M.E., S.E. Bentz, and R.T. Olsen. 2009. Evaluation of hemlock (Tsuga) species and hybrids for resistance to Adelges tsugae (Hemiptera: Adelgidae) using artificial infestation. Journal of Eco- nomic Entomology 102:1247–1254. Raupp, M., R. Ahern, B. Onken, R. Reardon, S. Bealmear, J. Doccola, P. Wolfe II, and P. Becker. 2008. Efficacy of foliar applications, trunk injections, and soil drenches in reducing populations of elongate hemlock scale on eastern hemlock. Arboriculture & Urban Forestry 34:325–329. Varela, L.G., R.S. Cowles, and D. Donaldson. 1996. Spring insecticide treatments control adelgids on Douglas-fir. California Agriculture 50(5):34–37. Weston, P.A., and R.W. Harper. 2009. Potential of Tsuga spp. from west- ern North America and Asia as replacements for eastern hemlock (Tsuga canadensis). Arboriculture & Urban Forestry 35:5–9. ©2013 International Society of Arboriculture
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