Planting date is an important management tool that influences winter wheat (Triticum aestivum L.) performance in the Northern Great Plains. A study was conducted to: (i) evaluate the effect of planting date on grain yield and agronomic traits of eight winter wheat cultivars varying in season length and winter hardiness; and (ii) determine if any interaction between cultivar and planting date exists. The study was located near Wall (43.99 degrees N, 102.24 degrees W) in western South Dakota from 2005 through 2007. Winter wheat cultivars were planted at five planting dates ranging from mid-September to early December. The response of winter wheat grain yield to planting date was quadratic, with the optimum planting date for maximum yield varying among winter wheat cultivars. Optimum planting dates for early and medium maturing cultivars ranged from 7 September to 19 October. For the late maturing cultivar, optimum planting dates ranged from 5 to 20 October, narrower than the current recommendations. The grain yields for early, medium, and late maturing cultivars were similar at early and intermediate planting dates, suggesting that in early planting situations, the season length of the winter wheat cultivar is not an important determinant of yield. The late maturing cultivar yielded lower than early or medium maturing cultivars when planting was delayed to dates later than mid-October in all 3 yr. Yield reduction with delayed planting was mostly due to a reduction in head density. Kernels per head increased with delayed planting but the increase was not enough to compensate for low tiller production in late-planted wheat.
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