Residual presence and impact assessment of herbicide for gorse control at long point reserve, Tasmania, Australia

Gorse (Ulex europaeus) is an invasive weed managed extensively throughout temperate areas of the world. At Long Point Reserve on the east coast of Tasmania, management has been highly effective, reducing the cover of the gorse population by 90% using cut-and-paint applications of glyphosate and spot-spraying of GrazonTM Extra. Considerable quantities of GrazonTM Extra have been applied repeatedly over a 10-year period and there is concern over whether the herbicide is persisting in the soil and impacting native plant recruitment. We collected soil samples and quantified plant species richness across sites with a range of spray frequencies. No herbicide residues were detected in the soil and plant species richness did not differ between treated and untreated areas. Given the moderate persistence of the active ingredients of GrazonTM Extra (picloram and triclopyr), detection in the soil was expected; however, it appears these herbicides have either quickly dissipated, leached to other areas or the skill of the spray contractor resulted in little spray drift or excess herbicide application. This research suggests good practice chemical control of gorse does not negatively affect native species, although this may be situation-specific.