Selective, post-emergence, isourazole herbicide which upon conversion to the urazole inhibits protoporphyrinogen oxidase. Prepn: M. Yamaguchi et al., EP 273417; eidem, US 4906279 (1988, 1990 both to Kumiai Chem. Ind.; Ihara Chem. Ind.). Description of physical properties, toxicity, and activity: T. Miyazawa et al., Brighton Crop Prot. Conf. - Weeds 1993, 23. Conversion to active metabolite and mode of action study: T. Shimizu et al., Plant Cell Physiol. 36, 625 (1995). Field study as harvest-aid for cotton: R. G. Lemon et al., Proc. Beltwide Cotton Conf. 1999, 605.