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Title: ROLE OF HERBICIDE ABSORPTION, TRANSLOCATION, AND METABOLISM IN THE INTERACTION BETWEEN THIFENSULFURON AND IMAZETHAPYR IN SULFONYLUREA TOLERANTSOYBEAN

Author
item SIMPSON, DAVID - UNIV OF ILLINOIS
item STOLLER, EDWARD

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The newly-developed sulfonylurea-tolerant soybean (STS soybean) will be planted in substantial quantities in 1995. STS soybeans resist injury from applications of thifensulfuron, but are severely injured from applications of the tank mixture of thifensulfuron and imazethapyr. This tank mixture is widely used to control a broad spectrum of troublesome weeds in soybean. We conducted greenhouse and laboratory experiments to determine the physiological reasons for the injury from combined applications. We found that neither herbicide affected the absorption, translocation or metabolism of the other herbicide in STS soybean, and postulated that the crop injury resulted from an effect at the ALS (acetotacte synthase) enzyme, the site in the plant where these herbicides exert their toxic effect.

Technical Abstract: Greenhouse and laboratory experiments were conducted to determine if the synergistic interaction between imazethapyr and thifensulfuron in STS soybean involved enhanced absorption and/or translocation or reduced metabolism of one or both herbicides. Thifensulfuron at 4.4 g/ha and imazethapyr at 70 g/ha caused 0 and 28% injury to STS soybean plants 7 DAT, respectively, while the combination of both herbicides caused 50% injury 7 DAT. Imazethapyr had no affect on absorption of 14C-thifensulfuron into the first trifoliolate. The total amount and the direction of translocation of 14C was not affected by imazethapyr. Metabolism of 14C-thifensulfuron was rapid with less than 10% remaining after 24 h and was not affected by imazethapyr. Thifensulfuron did not affect the absorption of 14C-imazethapyr with 54% absorption occurring within 4 h. Metabolism and translocation of 14C-imazethapyr were not affected by the thifensulfuron. The interaction between thifensulfuron and imazethapyr does not involve changes in the absorption, translocation, or metabolism of either herbicide.