Weed Response in Winter Wheat Fields on a Gradient of Glyphosate Use in the Recent Past

In the discussion about glyphosate-based herbicides, the question of how repeated applications affect biodiversity has become prominent. However, approaches are lacking to assess direct glyphosate effects under real, on-farm field conditions. This paper focuses the effect of post-harvest and / or pre-sowing glyphosate use on weed density, richness, diversity and composition in arable cropping systems. An on-farm monitoring was conducted in Northeast Germany over the period 2014-2016. The pre-harvest weed survey took place on a total of 97 winter wheat fields. Farmers ' records of field management were obtained for the surveyed fields for the year in which a field was visited and also the nine previous years. A total of 66 species over the three survey years were identified shortly before harvest. Overall, the highest number of specimens were found for the species Viola arvensis Murray, Fallopia convolvulus (L.) ' A. Lo center dot ve and Polygonum aviculare L. This study provided evidence that intensive glyphosate use in the recent past significantly sinks species richness by 31% and the true diversity by 40%. In contrast, weed density and weed community composition were not affected by past glyphosate use intensity. Indeed, we found that glyphosate-based or inversion tillage-based cropping systems induce different weed community patterns. The results of this study provide one more piece in the puzzle for the assessment of the impact of glyphosate use on the environment.