TITLE:
Two-Pass Weed Management with Preemergence and Postemergence Herbicides in Glyphosate-Resistant Soybean
AUTHORS:
Nader Soltani, Robert E. Nurse, Peter H. Sikkema
KEYWORDS:
Biomass, Weed Density, Glyphosate, Profitability Analysis, Soybean
JOURNAL NAME:
Agricultural Sciences,
Vol.5 No.6,
May
19,
2014
ABSTRACT: There is little information on the efficacy and profitability of two-pass
weed control strategies in soybean when a preemergence (PRE) residual herbicide is followed by glyphosate applied late postemergence (LPOST) under Ontario, Canada environmental conditions. Ten field trials were conducted during 2011-2013 in
Ontario, Canada to determine the level of weed control, yield and net returns
of various preemergence/postemergence programs in glyphosate-resistant soybean.
Crop injury was 2% or less with the herbicides evaluated except for chlorimuron
+ flumioxazin (PRE) and pyroxasulfone + flumioxazin (PRE) which caused 4% and
7% visible injury in soybean, respectively. A single application of glyphosate
resulted in variable weed control (73% - 98%) while the sequential application
of glyphosate provided excellent weed control (98% - 100%). The control of all
weeds 8 WAA after the LPOST glyphosate application was equivalent regardless of
the PRE herbicide applied (96% - 100%). Soybean yield was equivalent to the
weed free control regardless of the PRE herbicide applied. Soybean yield was
lower than the sequential application of glyphosate with chlorimuron or
pyroxasulfone/flumioxazin PRE fb glyphosate LPOST. Generally net return with
the two-pass programs was equivalent to the sequential application of
glyphosate. Net returns were lower than the sequential application of
glyphosate with chlorimuron or s-metolachlor + flumetsulam followed by
glyphosate LPOST. Based on these results, a sequential application of
glyphosate or a two-pass program of a preemergence residual herbicide followed
by glyphosate LPOST are the preferred weed management programs in
glyphosate-resistant soybean. The two-pass programs have the potential to
reduce selection pressure for glyphosate-resistant weeds.