Summary:Rooted cuttings ofPyrus melanocarpa(Michx.) Willd. had a 3.5‐fold greater tolerance to soil‐applied hexazinone than those ofRubus hispidusL. in a greenhouse trial.R. hispidusaccumulated four times more14C‐label in the foliage following root uptake of14C‐hexazinone thanP. melano‐carpa. Here, the greater uptake and susceptibility ofR. hispiduswas related to its greater root:fol‐iage (weight) ratio compared to the tolerantP. melanocarpa. However, in whole plant metabolism studies employing younger plants there were no differences in14C accumulation in the leaves. Here14Chexazinone was converted to a number of hydroxylated and/or demethylated triazinone metabolites in both species following vacuum infiltration into leaf disks and root sections, or following root uptake in whole plants. A major difference in metabolism between the two species was the greater formation of the mono demethylated metabolite, B, [3‐cyclohexyl‐6‐methylamino‐l‐methyl‐l,3,5‐triazine‐2,4‐dione] inP. melanocarpawhich may also contribute to its greater tolerance. A loss of total14Clabel from all plant parts with time may reflect cleavage of t