Arboriculture & Urban Forestry 32(3): May 2006 123 glyphosate would be transported toward the roots. We can also speculate that in the dormant season, glyphosate would be less effective because it requires translocation to the roots and metabolic activity. February and March (dormant season) cut-stump applications of undiluted glyphosate as Roundup had lower efficacy than June and July applications (Zedaker et al. 1987), supporting this supposition. Practical Implications Overall mortality for all herbicide mixtures was high, with all mixes having over a 90% mortality rate with at least one application date. This level of performance is considered ef- fective for right-of-way vegetation management programs us- ing highly selective, individual-stem treatments (K. Finch, pers. comm.). Conversely, vegetation managers should rec- ognize that up to ∼10% of the treated trees may live after treatment, even when that treatment is properly applied and matched with application date. Practitioners should anticipate that some trees will survive, especially since all it takes is one tree in the wrong place to affect transmission system safety and reliability. As with any herbicide treatment, lack of uni- form coverage would increase the percentage of trees surviv- ing treatment. On power line rights-of-way in the Northeast, treating un- desirable hardwood trees in wetlands is made more difficult by the limited number of herbicides that are approved for use in these sensitive areas. Accord + Arsenal is an important herbicide mixture for use in wetlands (K. Finch, pers. comm.), and if given a choice for date of application, veg- etation managers should make Accord + Arsenal applications in the fall to optimize efficacy. Application technique and the amount of herbicide applied are important considerations for efficient use of materials, minimizing costs, and reducing potential nontarget effects of treatments. While the amount of herbicide used to treat the plots—12.6 L/ha (5.4 qt/ac)—was consistent with normal, operational use of cut-stump treatment in plots with over 1,600 treatable stems/ha (650 stems/ac) (K. Finch, pers. comm.), we observed that the amount of herbicide used var- ied by date and herbicide mix, but with no apparent reduction in percentage mortality. Patterns of percentage mortality and amount of herbicide used were not correlated. Herbicide may have been overapplied. One indication of overapplication was the quantity of herbicide applied for the Garlon 4 + Stalker treatment in April, which was nearly twice as much as any other treatment in the study. The pattern of variability we observed in the quantity of herbicide used suggests that herbicide use was strongly in- fluenced by hand-pump spray bottle versus trigger spray bottle. Variability may also have been influenced by appli- cation technique via different individuals within and between crews. The November crew using the trigger spray bottle tended to use less volume of herbicide than the June crew using the hand-pump spray bottle. In a separate study of the cut-stump treatments in June, we reported that nearly half of the herbicide was applied off-target in a 0.6 m (2 ft) diameter circular zone around the cut stump (Nowak and Ballard 2005). This is an important point when considering the rela- tively high concentration of active ingredient in the cut-stump treatments, especially for those herbicides with higher soil activity such as picloram and imazapyr. With awareness and proper equipment, it may be possible to significantly reduce the amount of herbicide used in cut-stump treatment while maintaining a high mortality rate. Future research in this area is warranted, including the testing of application equipment. In addition, because the study was intended to evaluate the operational application of these treatments, we did not control the dose of herbicide applied. We suspect that lower rates could be applied, especially for the Garlon 4 + Stalker treat- ment in spring, and still achieve a high percentage mortality, but this warrants further study. Our results and suggestions should also be evaluated for other regions and site conditions with additional target tree species. The treatments should also be evaluated for different years because weather conditions could affect how well herbicides perform. CONCLUSIONS Critical to the long-term success of right-of-way vegetation management are the continued advancements in basic and applied knowledge that allow vegetation mangers to make informed decisions when prescribing treatments. With the results from this study, vegetation managers can now make more informed decisions when selecting herbicide mixtures for different seasons: Garlon 4 + Stalker or Pathway from early spring to fall, or Accord + Arsenal in the fall. In addi- tion, minor refinements in application techniques and equip- ment have the potential to reduce the amount of herbicide used without adversely affecting the efficacy of the treatment, and these warrant further consideration. A high percentage mortality with operational cut-stump treatments on power line rights-of-way can be achieved over a wide range of treat- ment dates, from early spring to late fall, by selecting an appropriate herbicide mixture. Acknowledgments. We acknowledge the following people and or- ganizations for collegial and monetary support for this study: Dr. Larry Abrahamson, State University of New York; Dr. Ed Neu- hauser, Ken Finch (retired), and Craig Allen, Niagara Mohawk, a National Grid Company; and Tom Sullivan, National Grid; Kevin McLoughlin (retired), Lew Payne, and George Stranovsky, New York Power Authority; Dick Mider, New York State Electric and Gas; Mike Fleming, BASF; Mark Rice and Dave Berk, Dupont; and Bill Sherksnas, Dow AgroSciences. We thank the following people for their technical support: Anne Barlow, Dan Charlebois, Christine Chodoba, Christopher Deegan, Rafael Herrera, Carrie Lorenz, Jason Magoon, Katie Moller, Byung-Bae Park, Angela Tewksbury, Mat- thew Todd, and Heather (Whittier) Luczak. We thank Dr. Larry ©2006 International Society of Arboriculture
May 2006
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