Department of Plant Sciences

Previous model experiments under greenhouse conditions identified high weed density and short waiting times for sowing after glyphosate dessication as potential risk factors, mediating glyphosate phytotoxicity to non-target crops. To evaluate these factors under field conditions, a set of three field trials with different waiting times after pre-crop glyphosate application was conducted in non-tillage winter wheat cropping systems in Southwest Germany. Additionally, model experiments with short waiting time (2 d) and a high density of target weeds were performed, using a track-spraying device to simulate conditions for field application. Both, in model experiments and under field conditions, short waiting times after pre-crop glyphosate application resulted in lower germination, delayed or arrested plant development, reduced shoot biomass production, partly impaired micronutrient acquisition as well as intracellular accumulation of shikimate as physiological indicator of glyphosate toxicity. Thus, it can be concluded that short waiting times and high density of target plants can be considered as relevant risk factors for phytotoxicity of glyphosate to non-target crops No-tillage cropping systems seem to be associated with a particularly high sensitivity to glyphosate-induced damage of crop plants. Recommendations of waiting times appropriate to the cropping system should be considered as promising strategy to avoid harvest losses due to phytotoxicity, impaired growth and micronutrient deficiency. Further elucidation of environmental risk factors promoting the expression of crop damage is necessary.