Efficacy of Mechanical and Herbicide Control Methods for Scotch Broom (Cytisus scoparius) and Cost Analysis of Chemical Control Options

Scotch broom is an invasive leguminous shrub in California and other Pacific Northwest states, as well as New Zealand and Australia. It is highly competitive in forest and shrub communities and can significantly impact reestablishment of conifer forests. The objective of this experiment was to evaluate mechanical methods (Weed Wrench, lopping), several herbicides, and herbicide application techniques for control of Scotch broom in a premontane site in California. Three herbicides were evaluated (glyphosate, imazapyr, and triclopyr ester) for canopy reduction using foliar, drizzle, and basal bark treatments. All treatments were made in both fall and late spring. In addition, we conducted a cost analysis of the various herbicide treatments and application methods. Results indicate that both mechanical treatments were effective, but their optimum timing depended on soil moisture conditions. In addition, there were no significant differences among herbicides at both timings, among all rates, and for any application method. All herbicides provided effective control of Scotch broom. However, the cost analysis demonstrated that the drizzle application method with glyphosate was the most cost-effective treatment, due to low herbicide cost and reduced labor requirements. These results provide several options for Scotch broom control and give land managers considerable flexibility with timing, herbicide, and application technique in their management programs.