Conventional vs. Glyphosate-Resistant Cropping Systems in Ontario: Weed Control, Diversity, and Yield

Abstract

Glyphosate-resistant (GR) crops have been adopted rapidly since their commercial introduction, and with the increase in commercially available crops resistant to glyphosate, continuous use of the same herbicide mode of action is now possible in some crop rotations. A 6-yr study was initiated to investigate the effects of conventional herbicides compared with continuous use of glyphosate in GR or Roundup Ready corn and GR soybean in a corn–soybean and a corn–soybean–winter wheat rotation. Individual experiments were fully phased and established at three locations under conventional tillage (CT) and at two locations under no-tillage (NT). Results indicated that midseason weed ground cover was lower when weeds were controlled with glyphosate; however, in most cases, this did not result in improved corn or soybean yields. Within locations, species richness, which strongly influenced other diversity indicators, was most affected by the herbicide treatments. Including winter wheat in the crop rotation had little effect on corn and soybean weed ground cover, density, and community structure and only affected soybean yield. Moreover, no effects of herbicide system used in previous corn and soybean were observed in winter wheat, with the exception of species diversity in NT, where species diversity tended to be greater when weeds in previous corn and soybean were treated with conventional herbicides. After 6 yr, the effects of continuous use of GR crops in rotation were similar to those reported in previous studies; however, continued monitoring and longer-term investigations of these systems are necessary to detect the early stages of development of herbicide-resistant biotypes.

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

“…However, this study was conducted using small plot areas and may not represent potential changes that might occur on a field scale. Gulden et al (2009) compared conventional with GMHT cropping systems for weed control, diversity and yield. Overall, the 6-year study showed higher levels of weed control in systems using glyphosate than in systems using conventional herbicides.…”

“…Such measures can ensure the appropriate management of glyphosate on GMHT soybean, so that the evolution of resistant weeds is delayed. Scientific evidence showed that the selection pressure on weeds can be reduced by crop rotation (e.g., rotating glyphosate tolerant crops with non-glyphosate tolerant crops), using variable application rates and timing, applying a variety of herbicidal active substances with different modes of action, and by using non-herbicide weed control tools such as post-emergence cultivation and cover crops (Gressel and Segel, 1990;Liebman and Dyck, 1993;Gardner et al, 1998;Doucet et al, 1999;Cardina et al, 2002;Neve et al, 2003a,b;Nazarko et al, 2005;Beckie et al, 2006;Culpepper, 2006;Sammons et al, 2007;Gustafson, 2008;Owen, 2008;Werth et al, 2008Werth et al, , 2010Beckie and Reboud, 2009;Busi and Powles, 2009;Gressel, 2009;Gulden et al, 2009;Shaw et al, 2009;Meissle et al, 2010;NRC, 2010;Beckie, 2011;Owen et al, 2011;Wilson et al, 2011). Using combinations of different weed management practices in integrated and diverse systems will reduce the selection pressure of any single practice or product (Sammons et al, 2007;Green and Owen, 2011;Shaner et al, 2012).…”

Glyphosate-Resistant Cropping Systems in Ontario: Multivariate and Nominal Trait-Based Weed Community Structure

“…In CT experiments, no changes in the frequency of grasses or broadleaved weeds were observed, with the exception of soybean at Woodstock where the frequency of grasses increased. In NT experiments, midseason weed densities of broadleaved weeds tended to be greater in the glyphosate than the conventional herbicide systems (Gulden et al 2009) which suggests that the shift in taxonomic groups resulted from reduced efficacy of glyphosate on broadleaved species relative to grassy weeds. In GR cotton (Gossypium hirsutum L.), the lack of residual herbicides resulted in increases in the populations of annual grasses (Culpepper 2006).…”

“…A preplant glyphosate ''burndown'' was applied to all NT experiments. Conventional herbicides were applied after planting but before crop emergence, and in the GR systems one or two in-crop applications of glyphosate were applied (Gulden et al 2009). …”

Scientific Opinion on application (EFSA‐GMO‐CZ‐2008‐54) for placing on the market of genetically modified insect resistant and herbicide tolerant maize MON 88017 for cultivation under Regulation (EC) No 1829/2003 from Monsanto

“…Such measures could ensure the appropriate management of glyphosate on GMHT maize, so that the evolution of resistant weeds is delayed. Scientific evidence showed that the selection pressure on weeds can be reduced by crop rotation (i.e., rotating glyphosate tolerant crops with non-glyphosate tolerant crops), using variable application rates and timing, applying a variety of herbicidal active substances with different modes of action, and by using non-herbicide weed control tools such as postemergence cultivation and cover crops (Gressel and Segel, 1990;Liebman and Dyck, 1993;Gardner et al, 1998;Doucet et al, 1999;Cardina et al, 2002;Neve et al, 2003a,b;Nazarko et al, 2005;Beckie et al, 2006;Culpepper, 2006;Sammons et al, 2007;Gustafson, 2008;Owen, 2008;Werth et al, 2008;Beckie and Reboud, 2009;Busi and Powles, 2009;Gressel, 2009;Gulden et al, 2009;Meissle et al, 2010;NRC, 2010;Werth et al, 2010;Beckie, 2011;Owen et al, 2011;Wilson et al, 2011). Using combinations of different weed management practices in integrated and diverse systems will reduce the selection pressure of any single practice or product (Sammons et al, 2007;Green and Owen, 2011;Shaner et al, 2011).…”