EFFECT OF PREHARVEST APPLICATIONS OF GLYPHOSATE ON THE DRYING, YIELD AND QUALITY OF WHEAT

In experiments conducted from 1988 to 1990 at four locations in the Parkland zone of western Canada, the drydown of seed and foliage, seed yield, seed quality and baking quality of wheat (Triticum aestivum L.) following preharvest applications of glyphosate were compared with those following windrowing prior to harvest or direct cutting of the standing crop. Glyphosate was applied in late July to early September at rates of 0.45, 0.9 and 1.7 kg acid equivalent ha(-1) to wheat with seed moisture contents ranging from 80 to 11%. When compared with a standing crop, all glyphosate treatments applied at seed moisture contents above 25% slightly enhanced the drydown of wheat seed and foliage. Treatments applied at seed moisture contents below 25% had no effect on either seed or foliage drydown. Seed yields were generally greater from plots to which glyphosate was applied than from windrowed control plots, although in one of five experiments the reverse trend occurred. Increasing the rate from 0.45 to 1.7 kg ha(-1) had no effect on yield. Windrowing or applying glyphosate to wheat with a seed moisture content of 61% or more reduced yields more than windrowing or applying glyphosate at seed moisture contents below this level. In experiments where the wheat in both control and sprayed plots was direct cut at maturity, average yields decreased as the rate of glyphosate increased from 0 to 1.7 kg ha(-1). However, applications at seed moisture of 40% or less, caused little or no yield loss. There was little or no difference in 1000-seed weight, sample density, seed germination and protein content from plots sprayed with glyphosate at seed moisture contents below 40% than from control plots windrowed at the same moisture content or direct cut at maturity. Baking quality was not affected by any of the glyphosate treatments in experiments where the wheat was harvested by direct cutting.