Physiological Mechanisms in the Synergism between Thifensulfuron and Imazethapyr in Sulfonylurea-Tolerant Soybean (Glycine max)

Abstract

Greenhouse and laboratory experiments were conducted to determine if the synergistic interaction between imazethapyr and thifensulfuron in sulfonylurea-tolerant (STS) soybean involved enhanced absorption and translocation or reduced metabolism of one or both herbicides. Thifensulfuron at 4.4 g ha−1and imazethapyr at 70 g ha−1caused 0 and 28% injury to STS soybean 7 DAT, respectively, while the combination of both herbicides caused 50% injury 7 DAT. Imazethapyr had no effect on absorption of14C-thifensulfuron into the first trifoliolate. Imazethapyr did not affect absorption, translocation, or metabolism of14C-thifensulfuron. Metabolism of14C-thifensulfuron was rapid, with less than 10% remaining after 24 h, and was not affected by imazethapyr. Likewise, thifensulfuron did not affect the absorption, translocation, or metabolism of14C-imazethapyr. Therefore, the synergism between thifensulfuron and imazethapyr does not involve changes in the absorption, translocation, or metabolism of either herbicide.