Weed Control, Environmental Impact, and Economics of Weed Management Strategies in Glyphosate-Resistant Soybean

Abstract

With the number of glyphosate-resistant weed species increasing in North America and a lack of new herbicide chemistries being developed, growers are shifting toward using older herbicides that are more expensive and may be less environmentally friendly. Therefore, to determine which weed management strategies are most cost effective and have the lowest impact on the environment we evaluated the efficacy, environmental impact, and the profitability of several weed management strategies in glyphosate-resistant soybean over a 3-yr period (2007 to 2009) at three locations in southwestern Ontario, Canada. No visible injury to soybean was observed with the herbicide treatments evaluated. A sequential application of glyphosate consistently provided high levels of weed control (99 to 100%) at 56 d after treatment in comparison with one- or two-pass herbicide programs. Soybean yield did not differ between the two-pass herbicide programs and glyphosate applied early POST; however, a yield benefit was found with a sequential application of glyphosate or a PRE herbicide followed by glyphosate compared with glyphosate applied only at late POST. The two-pass herbicide programs had higher environmental impact (EI) (> 23) than the one-pass herbicide programs (< 15), except when imazethapyr was followed by or tank-mixed with glyphosate, which had an equivalent EI (∼ 14) to the one-pass herbicide programs. Not surprisingly because of the low purchase price of glyphosate, gross margins were highest for treatments that included glyphosate. However, to reduce the selection pressure on glyphosate-resistant weed biotypes, to reduce environmental impact, and to increase gross margins a combination of glyphosate with another mode of action would be most beneficial. In this study glyphosate + imazethapyr was the best alternative to a sequential two-pass glyphosate program.

Weed Control, Environmental Impact, and Net-Profit of Two-Pass Weed Management Strategies in Dicamba-Resistant Soybean (<i>Glycine max</i>) Using Conventional Tillage

“…Soybean yields were similar across weed management programs (P > 0.05; Table 7); seed yields were 95% to 100% of the weed-free control. These findings are consistent with those reported by Soltani et al [10], Stewart et al [12], and Van Gessel et al [35] who found similar soybean yields across two-pass weed control programs of a PP or PRE herbicide fb glyphosate POST.…”

“…These EI values fall in the range of low or medium environmental risk [12] [15]. Several herbicides that included multiple active ingredients or modes-of-action had only a slightly higher EI than glyphosate applied alone (900 g•ae•ha ) POST had an EI of 15.7.…”

Weed control and crop tolerance of micro-encapsulated acetochlor applied sequentially in glyphosate-resistant soybean

“…Persistence of acetochlor is affected by many factors, including soil organic matter, microbial degradation, and leaching (Beestman and Deming 1974;Gish et al 1995). Several studies reported that one-pass weed control programs are insufficient to provide season-long weed control in soybean, and that PRE followed by POST herbicide programs are required, especially to control weeds that emerge later in the season, such as common waterhemp (Nurse et al 2007;Stewart et al 2011). Acetochlor applied PRE followed by early-or late-POST was comparable with weed-free control, acetochlor applied sequentially three times, as well as flumioxazin plus chlorimuron applied PRE followed by acetochlor plus glyphosate applied POST.…”

Scientific Opinion on an application (EFSA‐GMO‐NL‐2005‐24) for the placing on the market of the herbicide tolerant genetically modified soybean 40‐3‐2 for cultivation under Regulation (EC) No 1829/2003 from Monsanto

“…(Streloke, 2011). On the basis of environmental impact indices, a large number of authors have claimed that some of the herbicidal active substances used on GMHT crops (e.g., glyphosate) have reduced environmental impacts compared with those applied on their conventional counterparts (Nelson and Bullock, 2003;Peterson and Hulting, 2004;Brimner et al, 2005;Brookes and Barfoot, 2006;Leroux et al, 2006;Kleter et al, 2007;Bonny, 2008Bonny, , 2011Devos et al, 2008;Arregui et al, 2010;Mamy et al, 2010;Stewart et al, 2011). However, the environmental impact indices used for these calculations are generally based on residuality, persistence and ecotoxicity characteristics, and do not relate to efficacy (e.g., van der Werf, 1996;Reus et al, 2002).…”