The link between farmers’ sowing date and herbicide management

This study presents an on-farm approach to investigate the impact of the sowing date on herbicide management in arable farming. Ten years of data (2012–2021) on the herbicide use and crop management practices of 4325 fields in north-eastern Germany were examined for winter barley, winter oilseed rape and winter wheat. We investigated whether the sowing date was related to the herbicide use intensity (described as Treatment Frequency Index, TFI) and mode of action (MoA) use (classified using the global HRAC classification).

While the sowing of winter barley and winter oilseed rape took place over a short period of two weeks, sowing dates for winter wheat were spread over two months from the beginning of September to the end of October.

Seventy-five percent of the winter barley fields were treated with HRAC group 2 herbicides and every second field was treated with herbicides in HRAC groups 15 and 3, respectively. Delayed autumn sowing of winter barley differing by 14 days decreased the in-crop use intensity of HRAC group 2 by up to 16%, for HRAC group 3 by up to 15% and for HRAC group 15 by up to 27%.

In contrast, the herbicide management did not relate to the time of sowing in winter oilseed rape, except for HRAC groups 14 and 15.

Ninety percent of the winter wheat fields were treated with HRAC group 2 herbicides and almost seventy-five percent with HRAC groups 15 herbicides, respectively. For winter wheat, our study provided evidence that delayed sowing dates in-mid October reduced the use intensity of HRAC group 2 by up to 41% and for HRAC 15 by up to 35%, respectively, compared with sowing at the beginning of September.

With regard to the European-wide efforts to reduce chemical pesticide use by 50% by 2030, we conclude that cultural weed control with a sowing date delay may be highly effective at meeting this requirement. Additionally, delayed sowing dates have the potential to reduce the use intensity of MoA with a high resistance risk.