Control of Volunteer Glyphosate-Resistant Canola in Glyphosate-Resistant Sugar Beet
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Date
2015-03
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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.