Effect of preharvest glyphosate application on seed and seedling quality of spring wheat (Triticum aestivum)

Studies were conducted to determine effects of preharvest applications of g lyphosate on the seed and seedling quality of 'Alpowa' and 'Penawawa' soft white spring wheat (Triticum aestivum) varieties. Glyphosate was applied at 0.62 or 0.89 kg ae/ha at the milk (Zadoks' scale 70 to 79), soft dough (Za doks' scale 85), or hard dough stage (Zadoks' scale 87) of wheat developmen t; 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 t o 77% depending on the year, variety, and glyphosate rate. Likewise, kernel weight and germination were affected only by glyphosate applications tit t he milk stage with reductions from 19 to 73% and from 2 to 46% for kernal w eight and percent germination, respectively, compared to untreated wheat. U sing wheat from harvest-aided glyphosate treatments at the milk stage as se eds the following year resulted in reductions ranging from 28 to 99%, 19 to 39%, and 12 to 97% for seedling density, plant height, and seed yield, res pectively, compared to seeds from untreated wheat. In this study, wheat see d and seedling quality following preharvest glyphosate applications were mo st greatly influenced by crop maturity stage at time of application than by herbicide rate or variety.