Studies were conducted to determine if altered absorption, translocation, or metabolism were the basis for the reduction in sulfonylurea herbicide efficacy on foxtail species when mesotrione was mixed with a sulfonylurea herbicide. Green foxtail and yellow foxtail plants were grown in the greenhouse and treated at the four-leaf stage with ¹⁴C-labeled nicosulfuron or rimsulfuron, applied alone or with mesotrione or mesotrione atrazine. Absorption of nicosulfuron was greater in green foxtail and yellow foxtail 7 d after treatment (DAT) when applied alone, compared with absorption when mixing the herbicide with mesotrione or mesotrione atrazine. When nicosulfuron was applied alone, 9% more of the nicosulfuron in green foxtail was translocated at 7 DAT, as compared with when nicosulfuron was applied in combination with mesotrione or mesotrione atrazine. Translocation of nicosulfuron in yellow foxtail, however, was similar when nicosulfuron was applied alone or in combination with mesotrione or mesotrione atrazine. The addition of mixing rimsulfuron with mesotrione did not reduce the absorption of rimsulfuron in green foxtail 7 DAT, but the addition of mesotrione atrazine resulted in a 20% decrease in rimsulfuron absorption 7 DAT compared with absorption of rimsulfuron applied alone. Yellow foxtail absorption of rimsulfuron at 7 DAT was decreased by 11 or 20% when mixed with mesotrione or mesotrione atrazine, respectively. Application of rimsulfuron alone resulted in 6% more herbicide being translocated to the treated tiller in green foxtail at 7 DAT, compared with an application of mesotrione atrazine and rimsulfuron. Translocation of rimsulfuron in yellow foxtail was similar when applied alone or in combination with mesotrione or mesotrione atrazine. Nicosulfuron and rimsulfuron metabolism in foxtail species was similar when applied alone or in combination with mesotrione or mesotrione atrazine.

Nomenclature: Atrazine; mesotrione; nicosulfuron; rimsulfuron; green foxtail; Setaria viridis (L.) Beauv. SETVI; yellow foxtail; Setaria glauca (L.) Beauv. SETLU