Translocation of Nicosulfuron and Dicamba in Hemp Dogbane (Apocynum cannabinum)¹

Absorption and translocation of nicosulfuron and dicamba applied alone and combined was studied in 25-cm-high hemp dogbane originating from lateral roots that had overwintered. Absorption of C-14-nicosulfuron by hemp dogbane was not affected by applications of 70 g ai/ha unlabeled dicamba, Upward translocation of C-14-nicosulfuron in hemp dogbane was 86% greater 6 d after treatment (DAT) when dicamba was tank mixed with nicosulfuron, compared to nicosulfuron applied alone. Combinations of nicosulfuron plus dicamba increased translocation of nicosulfuron to hemp dogbane crown and roots 237 and 130%, 1 and 6 DAT, respectively, compared to nicosulfuron applied alone. Absorption of C-14-dicamba by hemp dogbane was not affected by the addition of 31 g ai/ha nicosulfuron. Upward translocation of dicamba in hemp dogbane was 42% greater 6 DAT for nicosulfuron plus dicamba compared to dicamba applied alone. Increased hemp dogbane control with nicosulfuron plus dicamba compared to either herbicide applied alone can be explained by enhanced translocation of both herbicides.