Agricultural Impacts of Glyphosate-Resistant Soybean Cultivation in South America

Abstract

In the 2009/2010 growing season, Brazil was the second largest world soybean producer, followed by Argentina. Glyphosate-resistant soybeans (GRS) are being cultivated in most of the soybean area in South America. Overall, the GRS system is beneficial to the environment when compared to conventional soybean. GRS resulted in a significant shift toward no-tillage practices in Brazil and Argentina, but weed resistance may reduce this trend. Probably the highest agricultural risk in adopting GRS in Brazil and South America is related to weed resistance due to use of glyphosate. Weed species in GRS fields have shifted in Brazil to those that can more successfully withstand glyphosate or to those that avoid the time of its application. Five weed species, in order of importance, Conyza bonariensis (L.) Cronquist, Conyza canadensis (L.) Cronquist, Lolium multiflorum Lam., Digitaria insularis (L.) Mez ex Ekman, and Euphorbia heterophylla L., have evolved resistance to glyphosate in GRS in Brazil. Conyza spp. are the most difficult to control. A glyphosate-resistant biotype of Sorghum halepense L. has evolved in GRS in Argentina and one of D. insularis in Paraguay. The following actions are proposed to minimize weed resistance problem: (a) rotation of GRS with conventional soybeans in order to rotate herbicide modes of action; (b) avoidance of lower than recommended glyphosate rates; (c) keeping soil covered with a crop or legume at intercrop intervals; (d) keeping machinery free of weed seeds; and (d) use of a preplant nonselective herbicide plus residuals to eliminate early weed interference with the crop and to minimize escapes from later applications of glyphosate due to natural resistance of older weeds and/or incomplete glyphosate coverage.

<b>Glyphosate efficacy on sourgrass biotypes with suspected resistance collected in GR-crop fields

“…Later, in 2008, sourgrass was identified as being glyphosate-resistant in GR-corn and -soybean fields in Paraná, Brazil (Heap, 2017). Since then, the number of resistant sourgrass cases has increased considerably in the country (Cerdeira, Gazziero, Duke & Matallo, 2011). The rapid adoption of GR crops and the loss of the glyphosate patent by Monsanto in 2000 were decisive factors for its widespread adoption as the main tool to control weed sin GR crops (Duke & Powles, 2008;Duke, 2017).…”

Use of genetically modified crops and pesticides in Brazil: growing hazards

“…Several factors associated with the cultivation of herbicide-resistant GM crops may contribute to the increased use of pesticides and losses in productivity, including biological vulnerability, weed resistance, and decreased soil fertility 14,[21][22][23][24][25][26][27][28][29][30] .…”

Sacred groves, sacrifice zones and soy production: globalization, intensification and neo-nature in South America

“…It is consumed more than any other agrochemical in Brazil, Argentina and other soy-producing countries in South America even though resistance to it is now widely reported (Nicholls and Altieri 1997;Binimelis, Pengue, and Monterroso 2009;Cerdeira, Gazziero, and Matallo 2011), and it has been identified by the World Health Organization (WHO) and multiple South American scholars as 'probably carcinogenic to humans' (Guyton et al 2015;Silva et al 2015), and associated with multiple other serious health problems (Marc et al 2004;Richard et al 2005;Benachour and Séralini 2009;Berger and Ortega 2010;Paganelli et al 2010;Moreira et al 2010;Oliveira et al 2014). Even breast milk in soy production regions has been contaminated by agrochemicals (Palma et al 2014).…”