Nutgrass herbicide management: results of two pot trials

Effective nutgrass control is crucial to maintain an optimal sugarcane yield. In the Mackay area, yield losses due to competition with nutgrass can be up to 27 % in dry land and up to 20% in irrigated systems. Several herbicide strategies were tested in pot trials in 2010 and 2011 to find the best option for long-term control of nutgrass. Both trials were arranged as randomised complete block designs with six replications, 13 herbicide strategies and untreated controls. Strategies included pre-emergent herbicides and / or post-emergent herbicides sprayed in one or two applications. In the two trials, both single and double applications of Roundup CT (450 g/L glyphosate) were very efficient in regard to desiccation of aerial parts and reduction of the production of active tubers by 78-98%. Viability of the tubers produced was also reduced (0-42%). Sempra (750 g/kg halosulfuron-methyl) at 90 g/ha reduced by 90-92% the production of active tubers and only 0-25% of these were viable (viability of tubers in untreated controls was 95%-97%). However, only a slow and modest impact was visible on aerial parts. Hero (ethoxysulfuron 600 g/kg) impacted on the production of active tubers by up to 98% and 0-20% of these were viable. With KrismatWG (trifloxysulfuron sodium 8g/kg, ametryn 731 g/kg), 87% fewer active tubers were produced but 17%-65% were still viable. Flame (imazapic 240 g/L) applied pre-emergence totally prevented the production of active tubers. When Flame was applied post emergence, the production of active tubers was reduced by 77%-88% and their viability ranged from 0 to 56%. Other tested products (2,4-D, MSMA, S-metolachlor) were not suitable long-term nutgrass management options. Further research is needed on Flame as it could potentially be an effective pre-emergent option for nutgrass control.