The effect of grazing date and time of spraying with a glyphosate/atrazine herbicide combination on a threeyear- old lucerne stand was studied on-farm in Central Otago. Total annual dry matter (DM) yield was highest in the weedy unsprayed control (14.8 t DM/ha) and lowest in the crop sprayed on 18 September (10.1 t DM/ ha). However, lucerne DM yield was highest from the 3 July and 22 August spray treatments (11.4 ± 0.39 t DM/ ha) and lowest in the unsprayed control at 7.7 t DM/ha. Phytotoxicity symptoms of glyphosate on the lucerne tended to be limited to crops sprayed on 18 September. To maximise yield, a winter clean-up grazing (June) followed by a winter herbicide application (July/August) when lucerne was approximately 3 cm high and with