Effectiveness of herbicide control methods for coyote brush on the North Coast of California

Coyote brush is a native shrub common on California coastal prairies. It is largely unpalatable to cattle and is an aggressive encroacher on open prairies; as such, it is a threat to livestock production on some of California’s most productive rangelands. This experiment assessed the effectiveness of four common herbicides and three application methods to control coyote brush. Glyphosate, imazapyr, triclopyr, and 2,4-dichlorophenoxyacetic acid (2,4-D) were analyzed using foliar spray and drizzle applications. Only glyphosate and imazapyr were analyzed using basal bark injection. All applications resulted in a short-term decrease in coyote brush cover, but plants that were treated with the selective herbicides triclopyr or 2,4-D appeared to recover after a year. The nonselective herbicides glyphosate and imazapyr performed well 12 months after application. Glyphosate and imazapyr performed similarly in controlling both large and small plants. No difference existed when comparing foliar spray and drizzle application methods, but both outperformed basal bark injection. As in previous studies, the drizzle method proved the most effective, requiring less labor and chemical than foliar application, and less threat of drift to non-target species. These results suggest that coyote brush can be controlled through both foliar spray and drizzle applications of glyphosate or imazapyr.