Pasture damage from spot-sprayed herbicides

Abstract

Spot-spraying weeds in pastures enables the use of herbicide that would be too harmful to pasture if boom-sprayed. However, some herbicides are more damaging than others. To quantify this damage, a range of spot-spraying treatments was applied to ryegrass/white clover pastures. Four herbicide treatments were compared, each at two application rates and two sizes of sprayed patch. Applications of either clopyralid or a triclopyr/picloram mix resulted in total removal of white clover from the sprayed patches but these patches remained covered in perennial ryegrass. Metsulfuron also removed all white clover but also severely damaged the perennial ryegrass, although some grass cover remained due to survival of browntop. Residues of these treatments suppressed seedlings of white clover and weeds for many weeks after application. Glyphosate treatments resulted in the most bare soil. White clover recovered most rapidly in glyphosate-treated areas, mainly by lateral spread of stolons, but weed species also established rapidly.