Sodium Bicarbonate Antagonism of Sethoxydim

Research was conducted to determine the influence of water carrier quality on grass control from sethoxydim. Water from a well near Halliday, ND, where sethoxydim failed to control grasses, contained 650 mg/L sodium and 1650 mg/L bicarbonate. Both sodium bicarbonate and sodium carbonate when included in the sethoxydim spray reduced grass species control in the greenhouse and field. Sodium carbonate in the spray generally was more antagonistic than sodium bicarbonate to sethoxydim toxicity to grasses. The antagonism from sodium bicarbonate at 6000 mg/L was overcome by diammonium sulfate or ammonium nitrate at 2.8 kg/ha or a 28% nitrogen liquid fertilizer at 9.4 L/ha in the sethoxydim spray. These compounds also overcame sodium carbonate and partly overcame the antagonism of sethoxydim by bentazon. Three commercial adjuvants for use with sethoxydim differed in their effect on wheat and oats control with sethoxydim alone or with bentazon.