Selective Weed Control with Glyphosate in Glyphosate-Resistant Spring Wheat (Triticum aestivum)1

Glyphosate-resistant spring wheat is being developed and may soon be available to growers. Field experiments were conducted to examine the effect of various rates and application timings of glyphosate on the tolerance of glyphosate-resistant spring wheat and the level of weed control attained with glyphosate in wheat. Glyphosate-resistant wheat exhibited excellent tolerance to glyphosate applied at the one- to two- or four- to five-leaf stages at rates up to 1,780 g ae/ha, representing a fourfold safety margin to the proposed field use rate. Glyphosate at 445 g/ha reduced shoot biomass of green foxtail, wild oat, redroot pigweed, and wild mustard > 95% in glyphosate-resistant wheat in all years, but wild buckwheat biomass was only reduced 67 to 75% at doses up to 890 g/ha. Glyphosate applied in-crop at 667 g/ha reduced quackgrass biomass by 97 to 99%. Comparison of glyphosate with other spring wheat herbicides indicated that glyphosate provided similar or better in-crop control of several weed species. Yield of weed-infested glyphosate-resistant spring wheat responded positively to glyphosate in all years.Nomenclature: Glyphosate; green foxtail, Setaria viridis (L.) Beauv. #3 SETVI; quackgrass, Elytrigia repens (L.) Nevski # AGRRE; redroot pigweed, Amaranthus retroflexus L. # AMARE; wild buckwheat, Polygonum convolvulus L. # POLCO; wild mustard, Brassica kaber (DC.) L.C. Wheeler # SINAR; wild oat, Avena fatua L. # AVEFA; spring wheat, Triticum aestivum L. ‘Bobwhite’, ‘BW251’.Additional index words: Herbicide resistance, wheat tolerance, wheat yield.