Effect of Preharvest Glyphosate Application on Seed and Seedling Quality of Spring Wheat (Triticum aestivum)1

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Abstract
Studies were conducted to determine effects of preharvest applications of glyphosate on the seed and seedling quality of ‘Alpowa’ and ‘Penawawa’ soft white spring wheat (Triticum aestivum) varieties. Glyphosate was applied at 0.62 or 0.84 kg ae/ha at the milk (Zadoks' scale 70 to 79), soft dough (Zadoks' scale 85), or hard dough stage (Zadoks' scale 87) of wheat development; 7 d following the hard dough treatment; and 1 d prior to wheat harvest. In harvest aid applications, wheat yields were reduced only with glyphosate applied at the milk stage of development. Yield reduction ranged from 20 to 77% depending on the year, variety, and glyphosate rate. Likewise, kernel weight and germination were affected only by glyphosate applications at the milk stage with reductions from 19 to 73% and from 2 to 46% for kernal weight and percent germination, respectively, compared to untreated wheat. Using wheat from harvest-aided glyphosate treatments at the milk stage as seeds the following year resulted in r...