Diffusive Resistance and Transpiration of Quackgrass (Elytrigia repens) Following Postemergence Herbicides

An established alfalfa stand infested with quackgrass received fluazifop-P, haloxyfop, or quizalofop at single applications of 0.28 ae kg ha-1and sequential applications of 0.14 plus 0.14 ae kg ha-1with the second treatment being made 16 d after the first. All herbicide treatments increased diffusive resistance and decreased transpiration of quackgrass compared to control plants. These effects became apparent 16 d or more after spraying. Visual injury symptoms were noted 8 to 10 d after treatment, several days prior to changes in diffusive resistance or transpiration. The alfalfa content of the first cutting was increased from herbicide treatment; however, total forage yield was reduced. Yields and composition of later cuttings were unaffected by the various herbicide treatments.