Antagonistic effects of 2,4‐D amine and bentazone on control of Avena fatua with tralkoxydim

Summary: Control of Avena fatua with tralkoxydim was significantly reduced in glasshouse experiments when the herbicide was tank‐mixed with either 2,4‐D amine or bentazone. Antagonism increased with increasing rates of these broadleaf herbicides in the tank‐mixture and it could, in turn, be decreased by increasing rates of tralkoxydim. When herbicide solutions were applied to single leaves with a micropipette applicator, bentazone was antagonistic only when mixed in the same droplet with tralkoxydim and not when the two herbicides were applied adjacently in separate droplets. In contrast, both separate and combined applications of 2,4‐D amine and tralkoxydim were antagonistic. There was no antagonism when mixtures with either 2,4‐D amine or bentazone were applied between the leaf sheath and culm. Antagonism could be circumvented by sequential applications of the herbicides. When tral‐oxydim was applied first, there was no loss of A. fatua control if bentazone application was delayed 0.5 h or if 2,4‐D amine was delayed 24 h. Results suggest that bentazone affects only cuticular penetration of tralkoxydim, whereas 2,4‐D amine also influences subsequent translocation.