RELATIVE FOLIAR UPTAKE OF A TANK MIXTURE OF 2,4-D AND DICAMBA BY WHEAT

Leaf washing was used to determine relative rates of uptake of 2,4-D and dicamba dimethylamine salts by wheat following field application of a postemergence tank mixture (3:1) of 476 g ae ha(-1) at the 4- to 5-leaf growth stage. Foliar herbicide deposits and total acid residues in the crop were determined the day of spraying as well as 2 and 7 d after spraying. Leaf washing of foliage samples collected on the day of spraying indicated that the crop/weed canopy intercepted 51% of the application, and that dicamba was taken up more quickly than 2,4-D. Within a few hours of spraying, approximately 80% of the deposited dicamba and 65% of 2,4-D were taken up by the crop. A 35-mm rain during the first 48 h after application reduced plant surface deposits of both herbicides by more than 98%. During this 2-d period, dicamba residues within the crop were metabolized more quickly than those of 2,4-D. There was little difference in effectiveness among water, 10% methanol, 25% methanol, or 90% methanol in removing plant surface deposits of 2,4-D and dicamba from wheat.