Arboriculture & Urban Forestry 32(3): May 2006 119 treatments have also been used in forestry for precommercial thinnings during the dormant season (Troth et al. 1986). In contrast to forestry applications, power line right-of-way treatments require very high mortality due to the potential impacts that surviving trees could have on the safe and reli- able transmission of electricity. Although utility foresters will likely have their own acceptable level of mortality, having over 90% mortality for cut-stump treatments is often consid- ered effective for right-of-way vegetation management (K. Finch, pers. comm.). Use of different herbicides, alone or in mixtures, may al- low for greater flexibility in tailoring treatments to specific site and vegetation conditions and time of the year. Because many tree species are typically encountered during opera- tional vegetation management of rights-of-way, herbicide mixtures may provide a wider spectrum of control, killing more species than a single-herbicide treatment. For example, if one of the herbicides in the mix is not very effective on a particular species, the other herbicide(s) may be. There has been little research evaluating date of cut-stump application using mixtures of herbicides. Knowing which herbicide mixes work best as a cut-stump treatment early in the spring and late in the fall would give more flexibility to vegetation managers in prescribing and scheduling treatments. The primary objective of our study was to determine what herbicide mixes could be operationally applied using the cut- stump treatment method at different times of the year to ef- ficaciously control common hardwood tree species in the Northeast. We evaluated efficacy, measured as percentage of mortality, of April, June, and November operational-style ap- plications of cut-stump treatments with three herbicide mixes: Accord (glyphosate) + Arsenal (imazapyr), Garlon 4 (tri- clopyr) + Stalker (imazapyr), and Pathway (2,4-D and picloram). We expected that greater than 90% mortality could be achieved at each date of application but hypothesized that some herbicides would be more efficacious than others at different times of the year because of differences in their mode of action. A secondary objective was to quantify the amount of herbicide applied by the operational crews to en- sure that typical amounts of herbicide had been used to kill right-of-way trees. We expected that the amount of herbicide used would be comparable among treatments. MATERIALS AND METHODS Study Area Description The study was conducted from spring 2000 through late sum- mer 2002 on the Volney-Marcy power line corridor in the towns of Lee, Western, and Floyd in Oneida County, New York, U.S. (43°21’N, 75°32’W to 43°15’N, 75°17’W). The Volney-Marcy corridor is a 70 m (230 ft) wide, 765 kV transmission line right-of-way constructed in 1982 to 1983. The right-of-way passes through the Interlobal Highland Re- gion, between the Tug Hill Plateau and the Mohawk Valley. It is surrounded by northern hardwood forest with a predomi- nance of red maple (Acer rubrum) and eastern hemlock (Tsuga canadensis) and a mixture of both abandoned and active agricultural land, resulting in a population of common shade-intolerant, early-successional tree species. Three study blocks were located approximately 6 to 18 km (3.6 to 10.8 mi) apart across a 24 km (14.4 mi) length of the right-of-way. Experimental Design Three treatment dates and three herbicide mixes were evalu- ated using a 3 × 3 factorial experiment in a randomized complete block design. The three blocks were designed to account for variability associated with people (applicators), time of application within a day, and tree size and density (vegetation conditions) among plots. Herbicide mix and date of application effects were tested for percentage mortality and amount of herbicide associated with cut-stump treatment of common right-of-way trees. Gray birch (Betula populifolia) was the dominant target species (41%), followed by pin cherry (Prunus pensylvanica, 18%), black cherry (Prunus serotina, 17%), red maple (A. rubrum, 14%), and quaking aspen (Populus tremuloides, 7%). Average stump diameter was 8.5 cm (3.4 in) across all treatment plots, ranging from 5.6 to 11.7 cm (2.24 to 4.68 in). Herbicide mixes used were Accord + Arsenal, Garlon 4 + Stalker, and Pathway (Table 1). Treatment dates for all three herbicide mixes were 19 April, 26–27 June, and 28 November. The 27 treatment plots (nine per block) averaged 0.04 ha (0.10 ac) in size, ranging from 0.02 to 0.11 ha (0.05 to 0.28 ac). Results were based upon individual tree measurements and are reported as percentage mortality and amount of herbicide used on per-acre or per- tree basis, and thus not sensitive to plot size. Treatments Treatments were applied using operational spray crews on contract with Niagara Mohawk, a National Grid Company (formerly Niagara Mohawk Power Corp.). Two-person crews applied the treatments—one person felled trees with a chain saw, and the other followed, immediately spraying herbicide. Accord + Arsenal and Pathway treatments were applied using a hand-pump spray bottle [Tolco pump-up spray applicator, ∼2 L (2.12 qt)] in April and June and a generic trigger spray bottle [∼500 mL (17 fl oz); different crew] in November. Garlon 4 + Stalker treatment applications at all treatment dates were made using Birchmeyer hand-operated backpack sprayers equipped with a basal wand, consistent with the application methods for this mixture (Table 1). Data Collection Before treatment, ten trees were chosen across each plot at random. The trees were stratified across the range of tree sizes and species. Each combination of herbicide mix and ©2006 International Society of Arboriculture
May 2006
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