Arboriculture & Urban Forestry 33(6): November 2007 425 roughly 100 ppm in the water taken up by the stem should result in 100% mortality of HWA (Cowles et al. 2006). Ef- fective xylem sap concentration reported by Cowles et al. (2006) could be combined with our estimates of daily water use by hemlock to calculate dosages that would result in consistent concentrations for hemlocks of various sizes grow- ing under various climatic conditions (Figure 4). Although our results suggest that current dosage recommendations yield sap concentrations that may be too low in large trees for maximum effectiveness, our results are speculative because we have not validated this (e.g., we have not measured con- centrations in the tissues or measuredHWAmortality). Cause and effect understanding will require detailed studies of the mechanisms underlying imidacloprid translocation. Until these cause and effect relationships are known, concentra- tions of AI in hemlock xylem sap may be a good indicator of the efficacy of injections, and dosage recommendations by the pesticide manufacturers could be refined with the addi- tional information provided by our water use models. The models presented here may also help practitioners de- termine injection depth and application timing throughout the range of eastern hemlock. Our data show that more than 50% of the water movement in the stem occurs in the outer 2 cm (0.8 in) of the xylem. Ensuring that injections do not pen- etrate deeper than 2 cm (0.8 in) will limit stem wounding and maximize potential delivery. In addition, because water use varies seasonally, the timing of stem injections may deter- mine the efficacy of treatment. For example, in the SA, if stem injections are timed to occur during peak water uptake and transport (e.g., April), then potential delivery of the in- secticide to the xylem ray parenchyma at the base of the needles will likely coincide with peak feeding activity of HWA (Ward et al. 2004). The water flux data and models may be useful in improv- ing the effectiveness and efficiency of systemic insecticide applications in eastern hemlock. More complex and robust models have been developed to predict eastern hemlock water use in the southern Appalachians (Ford and Vose 2007). However, our goal in developing the models presented was to create tools that could be used by tree care professionals to easily estimate eastern hemlock water use. Because these models were developed using transpiration data for healthy eastern hemlocks measured on rain-free days, the model pre- dictions are most relevant under similar conditions. Lastly, our data show: 1) that maximum water movement occurs 1 to 2 cm (0.4 to 0.8 in) past the inner bark; 2) that seasonal patterns of water use by eastern hemlock vary considerably from region to region, with maximum water use occurring in the spring (March to May) in the southern portion of the range and in the summer (June to August) in the northeastern portion of the range; and 3) water use is exponentially related to tree size. Copyright Statement This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright. Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans, ani- mals, and plants. Follow the directions and heed all precau- tions on the labels. Store pesticides in original containers under lock and key, out of the reach of children and animals, and away from food and feed. Apply pesticides so that they do not endanger humans, livestock, crops, beneficial insects, fish, and wildlife. Do not apply pesticides when there is dan- ger of drift, when honey bees or other pollinating insects are visiting plants, or in ways that may contaminate water or leave illegal residues. Avoid prolonged inhalation of pesti- cide sprays or dusts; wear protective clothing and equipment if specified on the container. If your hands become contami- nated with a pesticide, do not eat or drink until you have washed. In case a pesticide is swallowed or gets in the eyes, follow the first aid treatment given on the label and get prompt medical attention. If a pesticide is spilled on your skin or clothing, remove clothing immediately and wash skin thor- oughly. Do not clean spray equipment or dump excess spray material near ponds, streams, or wells. Because it is difficult to remove all traces of herbicides from equipment, do not use the same equipment for insecticides or fungicides that you use for herbicides. Dispose of empty pesticide containers promptly. Have them buried at a sanitary landfill dump or crush and bury them in a level, isolated place. NOTE: Some states have restrictions on the use of certain pesticides. Check your state and local regulations. Also, be- cause registrations of pesticides are under constant review by the Federal Environmental Protection Agency, consult your county agricultural agent or state extension specialist to be sure the intended use is still registered. Acknowledgments. We thank M.E. Montgomery and R.M. Hub- bard for helpful comments on an earlier version of this article. LITERATURE CITED 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. Daley, M.J., N.G. Phillips, J.C. Pettijohn, and J.L. Hadley. Water use by eastern hemlock (Tsuga Canadensis) and black birch (Betula lenta): Implications of effects of the hemlock woolly agelgid. Canadian Journal of Forest Re- search (in press). Doccola, J.J., I. Ramasamy, P. Castillo, C. Taylor, and S. Sifleet. 2005. Erratum: Efficacy of Arborjet VIPER mi- croinjections in the management of hemlock woolly ad- ©2007 International Society of Arboriculture
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