Effects of swathing on yield and quality of spring canola in northern Idaho

Spring canola (Brassica napus L.) is a new crop in the Pacific Northwest and growers have adopted cultural practices used in western Canada where spring canola (or rapeseed) must be swathed to hasten maturity and avoid frost damage. The aim of this study was to evaluate the effect of preharvest swathing on the seed yield and seed quality, and determine the best time to swath in northern Idaho, if swathing is needed. Five spring canola cultivars were planted in 1992 and 1993 to compare seed yield and quality of swathed and direct harvest crops. In 1994, commercial agricultural machinery was used in larger plots, to compare seed yield and quality from three different swathing dates with direct harvest. In 1992, directly harvested canola had higher yields than swathed canola. The following year, yield of directly harvested and swathed canola were not different. in commercial scale trials, yield loss was linearly related to time of swathing with the least reduction occurring when swathed at 60 to 80% brown seed, and most yield loss occurring when swathed at 10 to 20% brown seed. Therefore, optimal swathing time would be when most seeds were brown. Swathing canola resulted in smaller seed and greater chlorophyll content. However, swathed crops had lower seed moisture content, which may ease harvest operations. We recommend that canola should only be swathed in northern Idaho in cool and wet growing seasons, where harvest is delayed.