Simultaneous canola windrowing and herbicide treatment improve the production of sequenced winter wheat

In the context of canola (Brassica napus L.)-winter wheat (Triticum aestivum L.) rotational systems, the timing of canola stubble availability and effective weed management play a crucial role in the production of a subsequent winter wheat phase. This study, conducted from 2018 to 2022 across the Canadian prairies, applied a genotype × environment × management framework to examine how manipulations to canola harvest management can help optimize winter wheat production. The factorial treatment structure included two canola hybrids (early- and late-maturing), three canola harvest management systems (early-timing and conventional windrowing at 40 % and 60 % seed color change, respectively, and straight-cutting at 10 % seed moisture), and three weed management treatments (pre-harvest herbicide for canola, pre-plant herbicide for winter wheat, and pre-harvest+pre-plant herbicides). Windrowing and pre-harvest herbicides were completed simultaneously by retrofitting the swather with an onboard sprayer. Across all 16 site-years, winter wheat planted after a late-maturing canola hybrid demonstrated comparable performance to that after early-maturing canola. However, delaying canola harvest reduced winter wheat yields. Conventional windrowing in conjunction with pre-harvest herbicide or pre-harvest+pre-plant herbicides improved winter wheat yields and enhanced weed management, while maintaining canola seed quality, as no herbicide residues were detected in the harvested seed. Our previous research indicated that in-crop herbicide applications are unnecessary due to the high competitiveness of winter wheat against weeds. This research reaffirms in-crop herbicides could be eliminated and underscores the competitiveness and sustainability that a winter wheat phase offers when integrated in Canadian Prairie cropping systems.