Grass Herbicide Efficacy as Influenced by Adjuvant, Spray Solution pH, and Ultraviolet Light

Research was conducted at the Brandon Research Centre to determine the effect of spray solution pH or adjuvants on the efficacy of two cyclohexanedione (CHD) herbicides, clethodim and tralkoxydim, and two aryloxyphenoxypropionate (APP) herbicides, fenoxaprop-P and quizalofop, and if ultraviolet light is a factor influencing their activity. CHD herbicide efficacy decreased as spray solution pH increased above 7. APP herbicide efficacy was not affected by spray solution pH, probably due to their formulation as proherbicide esters. The choice of adjuvant affected CHD herbicide efficacy but not APP herbicide efficacy. Amigo®, Canplus-411® plus ammonium sulfate, and Merge® were usually the most effective adjuvants with the two CHD herbicides. Physical removal of ultraviolet light did not improve APP herbicide efficacy but did improve CHD herbicide efficacy.