Timing of Cut-Stump Herbicide Applications for Killing Hardwood Trees on Power Line Rights-of-Way

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.