Metabolism of Imazethapyr (AC 263499) Herbicide in Corn

Imazethapyr [5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) nicotinic acid] is the active ingredient of imidazolinone PURSUIT herbicide. A confined plot field experiment was conducted to determine the metabolism of 14C-6-pyridine-labeled imazethapyr in imidazolinone-tolerant corn after a single postemergence treatment at a rate of 0.25 lb ae/A, which is equivalent to 4 times the recommended use rate. The total radioactive residue in the corn plant was 15.35 ppm at 0 h after treatment and declined very rapidly to 0.28 ppm by 15 days. The residue in mature stalk/cob and seed at harvest was 0.08 and 0.02 ppm, respectively. The transport of radioactive residues to seed was minimal. Imazethapyr is metabolized very rapidly in corn. The major metabolic pathway for imazethapyr in corn was oxidative hydroxylation at the alpha-carbon atom of the ethyl substituent on the pyridine ring to yield alpha-(hydroxyethyl)-imazethapyr. Further glucosidation of the hydroxyl group was a very minor pathway to the terminal residue in corn. Only a trace amount of radioactive residue was identified as unchanged parent compound in corn. Since this study was conducted at 4 times the use rate, any one of the residue components in corn from application at normal use rate would be insignificant or negligible