Foramsulfuron (AE F130360) is a sulfonylurea herbicide for postemergence control of grasses and some broadleaf weeds in corn. Greenhouse and laboratory experiments were conducted to determine the physiological basis for differential tolerance of corn hybrids to foramsulfuron. Differences in corn tolerance were quantified by determining the herbicide rate required to cause injury and reduce corn height by 15% (GR₁₅). Seven hybrids were screened in the greenhouse where GR₁₅ values indicated that the some of the corn hybrids were sensitive to foramsulfuron. All but one of these hybrids exhibited an increase in tolerance when the safener, isoxadifen-ethyl, was applied with foramsulfuron. Experiments using ¹⁴C-foramsulfuron were conducted to determine whether isoxadifen-ethyl affected foramsulfuron absorption, translocation, and metabolism in two of the corn hybrids. There was no difference in absorption between a sensitive hybrid Novartis 58D1 and a more tolerant hybrid Novartis 59Q9, but the addition of isoxadifen-ethyl increased foramsulfuron absorption in both hybrids 24 h after treatment. Less than 1 and 3% of the ¹⁴C-foramsulfuron was translocated to plant portions above and below the treated leaf, respectively. Differences in hybrid tolerance were primarily due to differential herbicide metabolism. Foramsulfuron metabolism, with and without isoxadifen-ethyl, was similar at 4 h after treatment for both the sensitive and tolerant hybrids. However, by 24 h after treatment the more tolerant hybrid metabolized foramsulfuron to more polar compounds to a greater degree than the sensitive hybrid.

Nomenclature: Foramsulfuron; corn, Zea mays L.