AbstractThe uptake and translocation of14C‐isoproturon (3‐p‐cumenyl‐1‐1,‐dimethylurea) in wheat (tolerant) and backgrass (sensitive) following foliar treatment under controlled environmental conditions were examined. The amount of14C‐isoproturon translocated through the xylem was about 10 times that translocated through the phloem in both wheat and blackgrass. However, 25.5% of the applied14C‐isoproturon was translocated in the xylem in blackgrass, compared with 8.9% in wheat.14C‐isoproturon did not respond significantly to induced sink‐demand in either species. Leaf‐disc autoradiograms revealed the absorption of14C‐isoproturon by the minor veins and translocation into the cut vein endings. No significant differences were found in between wheat and bla