AbstractThe absorption, translocation and metabolism of the selective pre‐ or early post‐ emergence herbicide epronaz (N‐ethyl‐N‐propyl‐3‐propylsulphonyl‐1,2,4‐triazole‐1‐carboxamide) were investigated using selected crop and weed species. The pattern of tolerance to epronaz of both germinating seeds and 10‐day‐old plants grown in nutrient solution, was found to be soybean (Glycine maxL.)>maize (Zea maysL.)>cotton (Gossypium hirsutumL.)>rice (Oryza sativaL.)>barnyard grass [Echinochloacrus‐galli(L.) Beauv.]. In all species, absorption and translocation of14C from a nutrient solution containing [14C]epronaz (0.02 μCi ml−1) increased with time. Autoradiographic and liquid scintillation analysis indicated the presence of radioactivity in the apical regions of all species after 4 h. Interspecies variation in uptake and distribution did not appear to be a major factor explaining selectivity, although the resistance of cotton may be partly due to compartmentalisation of14C in the lysigenous glands in stem and leaves. Analysis of extracts from plants treated with [14C]epronaz indicated the presence of epronaz, its major degradation product [3‐propylsulphonyl‐l,2,4‐triazole (BTS 28 768)]and certain unknown radio‐labelled compounds. The major metabolite (Unknown I) was believed to be a conjugate of certain plant components with either epronaz or BTS 28 768. The rate of formation of Unknown I corresponded to the relative resistance and susceptibility to epronaz of soybean, rice and barnyardgrass. The level of the herbicide remained much higher in cotton than in the other species, possibly reflecting compartmentalisation and inactivation of epronaz in the lysigenous glands. For maize, high levels of uptake, exudation and degradation