New Herbicides Developed to Fight Scotch Broom
Scotch broom is a large, non-native shrub that has invaded forest sites throughout the Pacific Northwest. Because it develops a long-lived seed bank, the species can persist on a given site for decades. In a series of growth chamber studies, three of the newer synthetic auxin herbicides (aminocyclopyrachlor, aminopyralid , and clopyralid) were compared for their ability to control germinating Scotch broom seedlings from simulated seed banks. Low rates of each herbicide (less than 50 percent of the maximum labeled rate) killed 60 percent to 80 percent of seedlings; whereas, maximum rates controlled up to 89 percent of seedlings. Cost per unit seedling mortality for aminopyralid was 57 percent of that for clopyralid and 42 percent of that for aminocyclopyrachlor. With half-lives of 30 to 50 days, the herbicides retained much of their efficacy throughout the 90-day duration of the studies, making them suitable for controlling germinating broom seedlings under field conditions. New herbicide treatments were identified to prevent regeneration of Scotch broom from existing seedbanks. Differences in cost effectiveness among the three products give vegetation managers clear choices for selection of a suitable treatment.
Forest Service Partners