Is there a Weed Shift in Roundup Ready Maize? (Poster Presentation at the 4^th International Workshop on PMEM of Genetically Modified Plants, Quedlinburg, Germany, 2010)

Abstract

Weed effects of the use of glyphosate were investigated in a 6-years field study of continuous transgenic herbicide-resistant maize rotation (2003–2008). It was conducted at three sites in Germany which differed in terms of soil, climate, field history, and consequently initial weed spectrum. The studies focussed on the comparison between local herbicide standards and split applications of Roundup Ready (360 g L^–1 glyphosate) applied at dosages of 1.5 + 1.5; 2 + 2 and 3 + 3 L ha^–1 Roundup Ready.

Concerning the potential changes in weed communities, the study indicated no negative effect on weed infestation, communities or diversity, of the glyphosate treatments compared to the local herbicide standard. Possible shifts of the abundances of individual species were more affected by the initial and site specific weed spectrum rather than the herbicide treatment. Similar results were seen for the Shannon’s diversity index and Shannon’s evenness index.

In sum, and looking at annual effects, it could be concluded from this study that 1) there are no statistically significant differences between local standard herbicide treatments and the glyphosate treatments assessed in this study on the mean values of seedbank, species richness, species diversity and dominance; 2) the data collected on the different parameters showed an enormous variability within sites and years; 3) a dosage of 3 + 3 L ha^–1 Roundup Ready avoids spread of less sensitive species like Chenopodium album and Urtica urens; 4) as far as the standard herbicides are efficiently applied, they will have the same effect as the Roundup Ready treatments.