Control of Volunteer Glyphosate-Resistant Canola in Glyphosate-Resistant Sugar Beet

Abstract

Occurrence of glyphosate-resistant (GR) canola volunteers in GR sugar beet is a management concern for growers in the Northern Great Plains. Field experiments were conducted at the Southern Agricultural Research Center near Huntley, MT, in 2011 and 2012 to evaluate effective herbicide programs to control volunteer GR canola in GR sugar beet. Single POST application of triflusulfuron methyl alone at the two-leaf stage of sugar beet was more effective at 35 compared with 17.5 g ai ha 1. However, rate differences were not evident when triflusulfuron methyl was applied as a sequential POST (two-leaf followed by [fb] six-leaf stage of sugar beet) program (17.5 fb 17.5 or 35 fb 35 g ha 1). Volunteer GR canola plants in the sequential POST triflusulfuron methyl–containing treatments produced little biomass (11 to 15% of nontreated plots) but a significant amount of seeds (160 to 661 seeds m 2). Ethofumesate (4,200 g ai ha 1) PRE followed by sequential POST triflusulfuron methyl (17.5 or 35 g ha 1) provided effective control (94 to 98% at 30 d after treatment [DAT]), biomass reduction (97%), and seed prevention of volunteer GR canola. There was no additional advantage of adding either desmedipham þ phenmedipham þ ethofumesate premix (44.7 g ha 1) or ethofumesate (140 g ha 1) to the sequential POST triflusulfuron methyl– only treatments. The sequential POST ethofumesate-only (140 fb 140 g ha 1) treatment provided poor volunteer GR canola control at 30 DAT, and the noncontrolled plants produced 6,361 seeds m 2, which was comparable to the nontreated control (7,593 seeds m 2). Sequential POST triflusulfuron methyl–containing treatments reduced GR sugar beet root and sucrose yields to 18 and 20%, respectively. Consistent with GR canola control, sugar beet root and sucrose yields were highest (95 and 91% of hand-weeded plots, respectively) when the sequential POST triflusulfuron methyl– containing treatments were preceded by ethofumesate (4,200 g ha 1) PRE. Growers should utilize these effective herbicide programs to control volunteer GR canola in GR sugar beet. Because of high canola seed production potential, as evident from this research, control efforts should be aimed at preventing seed bank replenishment of the GR canola volunteers. Nomenclature: Desmedipham; ethofumesate; glyphosate; phenmedipham; triflusulfuron methyl; canola, Brassica napus L.; sugar beet, Beta vulgaris L. Key words: Crop volunteer, glyphosate-resistant canola, glyphosate-resistant sugar beet, herbicide efficacy.