328 Wallis statistic22.67, P < 0.0001 (Figure 2). In 2006 only on the third sample date, 12 September, was a marginal level of significance found in the abundance of EHS among treatments; Kruskal-Wallis statistic 12.77, P < 0.047. An all pairwise comparison test failed to resolve differences among treatment means. Numerically, trees treated with pyriproxyfen, horticul- tural oil, and imidacloprid (Merit) had the fewest scales. DISCUSSION Early attempts to control EHS with mixtures of malathion and DDT met with limited success as a result of the multigenera- tional nature of this scale (Davidson and McComb (1958). Wall- ner (1962) was the first to report acceptable levels of control using foliar applications of dimethoate, carbaryl, and phospha- midon. These insecticides resulted in reductions of scales of 100%, 75%, and 89%, respectively. Dimethoate continues to be an effective insecticide for controlling elongate hemlock scale in nurseries and Christmas tree plantations. Heller and Kline (2005a) reported high levels of control of elongate hemlock scale on Frazer fir with multiple applications of dimethoate. The efficacy of horticultural oil as a management tool for armored scales on narrow-leaved evergreens such as hemlocks and pines is inconclusive. McClure (2002) recommended thor- oughly drenching hemlocks during spring and again in summer, if needed, with horticultural oil to reduce populations of EHS in managed landscapes. However, Heller and Kline (2005b) found single applications of horticultural oil ineffective in reducing populations of EHS on Canaan fir, Abies balsamea var. phaner- olepis. In the same study, a spring application of Distance also failed to control EHS (Heller and Kline 2005b). Applications of horticultural oil and chlorpyrifos provided moderate control of a related species of armored scale, Chionaspis heterophyllae, on needles of scots pine, Pinus sylvestris (Fondren and McCullough 2005). Regarding the use of imidacloprid (Merit) to control armored scales on conifers, Cooper and Cranshaw (1995) found that imi- dacloprid failed to provide control of pine needle scale on Aus- trian pine. Sadof and Sclar (2000) and Rebek and Sadof (2003) also found imidacloprid (Merit, Marathon) applied as a soil drench did not control euonymus scale on Pachysandra termi- nalis or Euonymus fortunei, but like in the current study, pyri- proxyfen (Distance) provided good levels of control of euony- mus scale (Rebek and Sadof 2003). In summary, foliar applications of pyriproxyfen and horticul- tural oil provided superior levels of control compared with soil drenches, trunk injections, or implants of insecticides for the control of EHS in a landscape setting. After foliar sprays, popu- lation reductions were rapid and lasted into the second growing season. We doubt that prolonged reductions were the direct re- sult of residual toxicity of these materials because we found no evidence for long residual activity of oil or pyriproxyfen in the literature. Instead, it appears that once scale populations are re- duced, several months or even years may pass before populations of EHS rebound. Imidacloprid applied as a soil drench shows some efficacy in reducing populations of EHS. The possibility that imidacloprid can reduce populations of EHS is intriguing. To document this effect convincingly will require further testing with a much larger sample of trees or with a sample of trees less variable in abundance of EHS than those used in this study. Acephate implants and trunk injections of dinotefuron did not reduce the abundance of EHS relative to untreated trees. ©2008 International Society of Arboriculture Raupp et al.: Reducing Populations of Elongate Hemlock Scale Acknowledgments. We thank two reviewers for comments that im- proved the manuscript. We thank Kate Laskowski for technical assis- tance. We thank the U.S. Forest Service, Forest Health Technology Enterprise Team for supplying funds to conduct this research. We also thank F.A. Bartlett Tree Expert Co., Creative Sales, Inc., Arborjet En- vironmental Horticulture, and U.S. National Arboretum for providing materials, study sites, and labor that supported this research. LITERATURE CITED Cooper, D., and W. Cranshaw. 1995. Pine needle scale control on Aus- trian pine, 1994. Arthropod Management Tests 20:17H–315. Davidson, J.A., and C.W. McComb. 1958. Notes on the biology and control of Fiorinia externa Ferris. Journal of Economic Entomology 51:405–406. Fondren, K., and D.C. McCullough. 2005. Phenology, natural enemies, and efficacy of horticultural oil for control of Chionaspis heterophyl- lae (Homoptera: Diaspididae) on Christmas tree plantations. Journal of Economic Entomology 98:1603–1613. Ford, C.R., J.M. Vose, M. Daley, and N. Phillips. 2007. Use of water by eastern hemlock: Implications for systemic insecticide applications. Journal of Arboriculture and Urban Forestry 33:421–427. Gardosik, S.M. 2001. Aspidiotus cryptomeriae Kuwana, an armored scale pest of conifers (Homoptera: Diaspididae). Regulatory Horti- culture 27:23–25. Garrett, W.T. 1965. The biology and control of the Fiorinia hemlock scale, Fiorinia externa (Homoptera: Diaspididae). University of Maryland. PhD Thesis. 106 pp. Heller, P.H., and D. Kline. 2005a. Multiple application study to suppress elongate hemlock scale with acephate and dimethoate on Fraser fir Christmas trees, 2003. Arthropod Management Tests 30:G30. ———. 2005b. Management study to suppress elongate hemlock scale with single applications of Ultra-fine oil, Distance, and M-pede on Canaan fir Christmas trees, 2003. Arthropod Management Tests 30:G23. Kosztarab, M. 1996. Scale Insects of Northeastern North America. Vir- ginia Museum of Natural History Special Publication.3. 650 pp. McClure, M. 1991. Adelgid and scale insect guilds on hemlock and pine, pp. 256–270. In: Baranchikov, Y.N., W.J. Mattson, F.P. Hain, and T.L. Payne (Eds.). Forest Insect Guilds: Patterns of Interaction With Host Trees. 13–17 August 1989; Abakan, Siberia, U.S.S.R. Gen. Tech. Rep. NE-153. U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station, Radnor, PA. McClure, M.S. 1977a. Resurgence of the scale, Fiorinia externa (Ho- moptera: Diaspididae) on hemlock following insecticide application. Environmental Entomology 6:480–484. ———. 1977b. Dispersal of the scale, Fiorinia externa (Homoptera: Diaspididae) and effects of edaphic factors on its establishment on hemlock. Environmental Entomology 6:539–544. ———. 1977c. Parasitism of the scale, Fiorinia externa (Homoptera: Diaspididae) by Aspidiotiphagus citrinus (Hymenoptera: Eulophidae) in hemlock: Density dependence. Environmental Entomology 6: 551–555. ———. 1978. Seasonal development of Fiorinia externa, Tsugaspidio- tus tsugae (Homoptera: Diaspididae), and their parasite, Aspidiot- iphagus citrinus (Hymenoptera: Aphelinidae): Importance of host– parasite synchronism to the population dynamics of two scale pests of hemlock. Environmental Entomology 7:863–870. ———. 1980. Competition between exotic species: Scale insects on hemlock. Ecology 61:1391–1401. ———. 2002. The Elongate Hemlock Scale. Pest Alert. USDA Forest Service. Northeast Area. NA-PR-01-02. McClure, M.S., and M.B. Fergione. 1977. Fiorinia externa and Tsu- gaspidiotus (Homoptera: Diaspididae); distribution, abundance, and
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