Estimated optimum seeding dates for winter wheat in Ontario

Winter wheat (Triticum aestivum L.) must be seeded during an optimum period in the fall to achieve maximum yields. Present recommendations for fall seeding based on corn heat unit zones for Ontario have not been satisfactory in all areas. Results from seeding-date trials at five locations across Ontario confirmed the concept of a 2-wk optimum seeding period (OSP) for winter wheat. A highly significant non-linear regression relationship (R 2 = 0.997) was established between the average optimum seeding date (OSD) for six locations in Ontario (taken as the mid-point of the OSP) and the average daily mean air temperature for the period 1 Sept. – 31 Oct. This relationship estimated OSDs more accurately for Ontario than a previously developed relationship based on data from across Canada. Climatic normals (1951–1980) data for more than 350 locations were used to construct 13 OSD zones for Ontario. Estimated OSD ranged from as late as 15 Oct. for the Windsor area to before 21 Aug. in the north around Kapuskasing. Average losses in yield from seeding after the OSP ranged from 75 kg ha −1 day −1 in southwestern Ontario to 40–65 kg ha −1 day −1 in eastern Ontario. Key words: Triticum aestivum L., optimum seeding date zones, climatic normals