118 Ballard and Nowak: Timing of Cut-Stump Herbicide Applications Timing of Cut-Stump Herbicide Applications for Killing Hardwood Trees on Power Line Rights-of-Way Benjamin D. Ballard and Christopher A. Nowak Abstract. Removal of tall-growing trees on power line rights-of-way is necessary for the safe and reliable transmission of electricity. Cut-stump herbicide treatments have been used at different times of the year to control resprouting and suckering of unwanted hardwood trees on power line corridors in the northeastern United States with varying degrees of success. Growing season applications have typically been thought to be most effective; however, if a high percentage of mortality could also be achieved by selecting an appropriate herbicide mix for early-spring and late-fall applications, vegetation managers would have more flexibility in prescribing and scheduling treatments. The authors evaluated mortality and amount of herbicide applied for April, June, and November using operational-style cut-stump treatments with three herbicide mixes—Accord + Arsenal, Garlon 4 + Stalker, and Pathway. After 2 years, over 90% mortality was achieved for at least one herbicide mix at all three application dates. Mortality varied by both mix and application date, consistent with herbicide mode of action. In April and June, Accord + Arsenal had lower mortality than Garlon 4 + Stalker or Pathway, but in November, it resulted in slightly higher mortality than the other two mixes. The Garlon 4 + Stalker mix and Pathway had equally high mortality for all treatment dates. Successful use of the cut-stump method in spring through fall may be contingent upon matching herbicide mix to the date of application. These results indicate that Garlon 4 + Stalker or Pathway could be used April through November, but applications with Accord + Arsenal should be made in late summer or fall. These recommendations should be evaluated in other regions and with additional target tree species. The quantity of herbicide used by operational crews varied among application dates and herbicide mixtures and appeared to be strongly influenced by spray equipment and the person applying the herbicide. Minor refinements in application techniques and equipment have the potential to reduce the amount of herbicide used without adversely affecting efficacy, and warrant further consideration. Key Words. Cut surface; electric transmission lines; glyphosate; herbicide use rates; imazapyr; picloram; triclopyr; 2,4-D; vegetation management. Electric transmission line rights-of-way are important tech- nological and ecological features of the landscape. The pri- mary purpose of these rights-of-way is to provide for the safe, reliable transmission of electricity. Active vegetation man- agement helps ensure that this purpose is met by controlling populations of tall-growing trees that can act as conduits for electricity and cause ground-fault disruptions in transmission. Using an Integrated Vegetation Management approach on rights-of-way to control tall-growing trees requires a broad suite of vegetation management treatments, including chemi- cal, physical and mechanical, and biological and ecological methods (McLoughlin 1997, 2002). Herbicides are important vegetation management tools for controlling hardwood trees that would otherwise resprout or sucker when using an alter- native method such as handcutting or mowing. Commonly used herbicide application methods include foliar, stem- foliar, basal, and cut-stump treatments (Gangstad 1989; Nowak et al. 1992, 1993; Abrahamson et al. 1995; Sulak and Kielbaso 2000). Cut-stump is an important method because it can be selectively applied with narrow zones of off-target herbicide deposition and minimal disturbance to desirable, nontarget plants (Nowak and Ballard 2005). Unlike many foliar and basal treatments, cut-stump treatments also have ©2006 International Society of Arboriculture low visual impacts (e.g., no brown-out or standing dead trees). Cut-stump treatments may be particularly useful in areas where off-target impact must be minimized, such as wetlands and riparian buffers. The cut-stump treatment combines the use of mechanical and chemical methods. The mechanical component is typi- cally done using a chain saw or brush saw to cut a stem near groundline. The herbicide application is typically made im- mediately, or soon after cutting within a specified period per label instructions. Depending on the herbicide mixture, the application is made either directly to the cambium, or to the cambium plus the bark, and any exposed roots. In the northeastern United States, cut-stump treatments have been applied operationally at different times of the year to control hardwood trees on power line rights-of-way with varying degrees of success (K. Finch, retired, Niagara Mo- hawk, a National Grid Co., pers. comm.). Operational use of the cut-stump method was thought to yield best results when applied during the growing season, but it has been applied with some success at other times of the year. Cut-stump treat- ments have been used for crop-tree release in forestry in the dormant and growing season, with some products working better in the dormant season (Zedaker et al. 1987). Cut-stump
May 2006
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