Wipe-On Herbicide Trial: Scotch Broom Control in a Grassland

Scotch broom (Cytisus scoparius) is one of the greatest threats to the biodiversity of South Puget Sound Prairies. The Nature Conservancy and the Washington Department of Fish and Wildlife began an herbicide trial for the control of Scotch broom on Scatter Creek Wildlife Area (SCWA) in south Thurston County. The trial was conducted to test late summer versus spring applications, two wipe on apparatuses, and two herbicides for controlling Scotch broom. The two wipe on applicators tested were the Weed/Sweep and Rotowiper. Roundup Ultra (glyphosate) and Garlon 4 (triclopyr ester) were applied with each applicator in late summer 2003 and spring 2004. Each applicator and herbicide achieved mortality rates above 50% in some tests. Garlon applied in the spring with the Rotowiper was the most effective with more than 90% mortality. However, the Rotowiper also caused 35% mortality in the native non-target Festuca roemeri, while the Weed/Sweep had no significant non-target mortality. The results of the trial indicate that the Rotowiper consistently achieves higher mortality rates with either herbicide but also causes mortality in non-target species. Each of the applicators control Scotch broom but neither is 100% effective. When used in in combination with other methods, both appear to be effective tools for controlling Scotch broom with minimal to medium non-target mortality.