BASIS OF SELECTIVITY OF THE HERBICIDE FLUPYRSULFURON-METHYL IN WHEAT

Flupyrsulfuron-methyl, methyl 2-[[[[(4,6-dimethoxy-2-pyrimidinyl) mino ]carbonyl]amino]sulfonyl]-6(trifluoromethyl)-3 -pyridinrcarboxylate mo nosodium salt, formerly DPX-KE459, is a new postemergence sulfonylurea herbicide for the control of grass and broadleaf weeds in wheat. Simi lar to other sulfonylureas, the sits of action of flupyrsulfuron-methy l is acetolactate synthase (ALS), an enzyme in branched-chain amino ac id biosynthesis. Studies of in vitro inhibition of ALS across sensitiv e and tolerant species discount differential active site sensitivity a s the basis for wheat tolerance to this herbicide. However, wheat and the tolerant weeds Avena fatua and Phalaris minor metabolized flupyrsu lfuron-methyl very rapidly with half-lives of less than or equal to 2 h. Metabolism in the moderately tolerant species Setaria viridis was i ntermediate (half-life of 10 h). and slow in Alopecurus myosuroides (h alf-life of 20 h), a sensitive species. The initial metabolic pathway of flupyrsulfuron-methyl in wheat primarily involves glutathione conju gation; whereas in an equally tolerant species, P. minor, this herbici de is not metabolized by glutathione conjugation but apparently by O-d emethylation. Flupyrsulfuron-methyl is metabolized via both pathways ( glutathione conjugation and O-demethylation) in A. fatua, also a toler ant species. Differential rates of metabolism in sensitive and toleran t plant species are responsible for the selectivity of flupyrsulfuron- methyl. (C) 1998 Academic Press.