Effect of Droplet Size and Herbicide Concentration on Absorption and Translocation of14C-2,4-D in Oriental Mustard (Sisymbrium orientate)

Individual droplets of14C-2,4-D dimethylamine (DMA) were applied to oriental mustard seedlings to determine the effect of droplet size and herbicide concentration on absorption and translocation 1 or 3 d after application. Absorption of14C-2,4-D was generally not affected by droplet size which ranged from 198 to 2760 μm. However, the percentage of absorbed14C-2,4-D that was translocated away from the treated leaf increased as droplet size decreased. Absorption of14C-2,4-D either increased slightly or was not affected by increased herbicide concentration, but translocation of absorbed14C-2,4-D was reduced as herbicide concentration increased. Absorption and translocation of14C-2,4-D DMA were reduced when applied after a drop of 21.3 mM commercially formulated 2,4-D had been applied at the same location on the leaf. These results indicate that large amounts of 2,4-D, either in the form of large droplets or a more concentrated herbicide solution, inhibit translocation of 2,4-D from oriental mustard leaves.