Field experiments were established to investigate the effects of tank-mixing sethoxydim or quizalofop with imazaquin, chlorimuron, or lactofen for barnyardgrass control in soybeans. Sequential applications, where the grass herbicide was applied 24 h before or after the broadleaf weed herbicide, were also evaluated. There was an antagonistic decrease in barnyardgrass control when sethoxydim or quizalofop was tank mixed with any of the broadleaf weed herbicides. Antagonism was also observed when either grass herbicide was applied 24 h after imazaquin or lactofen, but not with chlorimuron. Control was not affected when the grass herbicide was applied 24 h before the broadleaf weed herbicide. In greenhouse experiments, the effects of tank-mixing sethoxydim, quizalofop, fluazifop-P, haloxyfop, fenoxaprop, or clethodim with imazaquin, lactofen, chlorimuron, acifluorfen, fomesafen, bentazon, or 2,4-DB were also evaluated for barnyardgrass control. Although acifluorfen provided 45% barnyardgrass control, tank-mixing it with fluazifop-P, haloxyfop, or fenoxaprop was antagonistic. Antagonism also occurred when chlorimuron was tank mixed with any of the grass herbicides except fenoxaprop. Barnyardgrass control by all of the grass herbicides applied in the field or greenhouse was most severely antagonized by tank mixes containing imazaquin.