Comparisons of Genetically Modified and Non-Genetically Modified Soybean Cultivars and Weed Management Systems

Adoption of glyphosate-resistant crops and the use of glyphosate has resulted in the evolution of glyphosate-resistant weeds. The objective of the studies reported was to investigate yield and weed management systems of genetically modified (GM) and non-GM soybean [Glycine max (L.) Merr.] at three Iowa locations during 2007 and 2008. Yield of glyphosate-resistant, glufosinate-resistant, and non-GM cultivars was determined in six site–years. The non-GM cultivars yielded 315 and 265 kg ha−1 less than the glyphosate-resistant and glufosinate-resistant cultivars, respectively, while no differences between GM cultivars were observed. Weed management systems differed for the cultivars but had equivalent weed control (>90%). Weed management systems in the non-GM cultivars caused more phytotoxicity (36% versus approximately 5% 7 d after application) and, coincidentally, the non-GM cultivars had the lowest yields. No differences in phytotoxicity were observed among the weed management systems for the GM cultivars. Similarly, no differences in yield were observed comparing the weed management systems for the GM cultivars. The experiment locations did not have high weed population densities although the untreated controls yielded 48% less than the other weed management systems included in the studies. Given concerns for glyphosate-resistant weeds, the studies demonstrated that acceptable and equivalent options to glyphosate-resistant soybean exist to manage glyphosate-resistant weeds in maturity groups 2 and 3 soybean which represent the majority of the U.S. soybean production.