Using plant development to determine optimum times for spraytopping, and assessing effect of grazing and double/repeat herbicide applications on regeneration of vulpia
P.M. DowlingA,B, G.D. MillarB, B. MilneB,C and P. NewellB,D
A Charles Sturt University PO Box 883, Orange, New South Wales 2800, Australia.
B New South Wales Department of Primary Industries, Orange Agricultural Institute, Forest Road, Orange, New South Wales 2800, Australia.
C Smith Street, Molong, New South Wales 2866, Australia.
D Belubula Way, Canowindra, New South Wales 2804, Australia.
Control of vulpia, an annual grass weed of temperate Australian pastures, has relied on spraytopping in spring using sub-lethal rates of paraquat and glyphosate; and wintercleaning using simazine. For spraytopping, the application window is narrow and a more accurate and practical procedure for assessing optimum application times is required. This was examined in replicated field experiments on an annual pasture near Bathurst, NSW over three years where paraquat and glyphosate were applied on four occasions in each spring, and at each spray time, the stage of vulpia development recorded. Herbicide effectiveness was dependent on the proportion of tillers where the seedheads were visible (peeping), but varied with herbicide type. Control following glyphosate and paraquat was optimum at 70-80% peeping, and 80-90% peeping, respectively. Plant development was related to cumulative mean temperatures (R2 = 0.83) and provides another option for assessment of optimum application times. For their respective optimum application times, glyphosate was more effective than paraquat in controlling vulpia, but regeneration of subterranean clover was lower. Marginally greater control of vulpia was achieved by doubling recommended application rates, repeating applications in successive years and applying grazing pressure following herbicide application. However, when assessed 18 months after spraytopping and with no other restrictions to natural seeding, vulpia populations had significantly increased, indicating that spraytopping needs to be complemented by other management inputs for long-term control.
Keywords: glyphosate, paraquat, subterranean clover.
Plant Protection Quarterly (2009) 24 (1) 32-38.