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 Pa rkland zone of western Canada, the drydown of seed and foliage, seed y ield, seed quality and baking quality of wheat (Triticum aestivum L.) following preharvest applications of glyphosate were compared with tho se following windrowing prior to harvest or direct cutting of the stan ding crop. Glyphosate was applied in late July to early September at r ates 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 standi ng crop, all glyphosate treatments applied at seed moisture contents a bove 25% slightly enhanced the drydown of wheat seed and foliage. Trea tments applied at seed moisture contents below 25% had no effect on ei ther seed or foliage drydown. Seed yields were generally greater from plots to which glyphosate was applied than from windrowed control plot s, although in one of five experiments the reverse trend occurred. Inc reasing the rate from 0.45 to 1.7 kg ha(-1) had no effect on yield. Wi ndrowing or applying glyphosate to wheat with a seed moisture content of 61% or more reduced yields more than windrowing or applying glyphos ate at seed moisture contents below this level. In experiments where t he wheat in both control and sprayed plots was direct cut at maturity, average yields decreased as the rate of glyphosate increased from 0 t o 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 conten t from plots sprayed with glyphosate at seed moisture contents below 4 0% than from control plots windrowed at the same moisture content or d irect cut at maturity. Baking quality was not affected by any of the g lyphosate treatments in experiments where the wheat was harvested by d irect cutting.