Dose responses of glyphosate resistant and susceptible biotypes of sweet summer grass (Brachiaria eruciformis) at the early tiller growth stage – 2014

Abstract

Key findings • The first population of glyphosate resistant (GR) sweet summer grass, found near Emerald in central Queensland, can survive rates of glyphosate between 450 mL/ha up to 2 L/ha, 28 days after application. The registered rates of application for moderate sized plants is between 800 mL and 1.6 L/ha. • Rates as low as 250 mL/ha of glyphosate controlled susceptible populations under glasshouse conditions. • The resistant population appears to have at least an 8‑fold level of resistance as the extent of control with 250 mL/ha on a susceptible population was slightly higher than the response of 2 L/ha on a resistant population. • Growers in Central Queensland need to consider and use alternative control options for this weed to prevent or minimise the development of further such glyphosate resistant cases. • Plants grown under glasshouse conditions are likely to be more susceptible to herbicides and it is likely that glyphosate rates higher than 2 L/ha may not be enough to control GR sweet summer grass in the field, especially under less favourable conditions.