Control of Hemp Dogbane with Foliar and Soil Applied Herbicides

Hemp dogbane (Apocynum cannabinum L.) has become a serious weed problem in eastern and southcentral Nebraska. Greenhouse and field studies were conducted to evaluate control of hemp dogbane with herbicides. In greenhouse studies, postemergence applications of herbicide combinations which included 2,4-D [(2,4-dichlorophenoxy)acetic acid] ester, 2,4-D amine, or glyphosate [N-phosphonomethyl)glycine] controlled hemp dogbane more effectively than those containing dicamba (3,6-dichloro-o-anisic acid) or amitrole (3-amino-s-triazole). Control was greater with equivalent rates of 2,4-D ester than with 2,4-D amine. Control with 2,4-D increased with longer slide-chain lengths of both ester and amine formulations. Postemergence control of hemp dogbane with herbicides was erratic in field studies over years. Glyphosate generally provided better control than 2,4-D, and amitrole consistently gave poor control. A preliminary study showed that growth of hemp dogbane from crown and lateral roots could be suppressed or controlled with preplant treatments of thiocarbamate herbicides. Increasing order of effectiveness for controlling hemp dogbane was vernolate (S-propyl dipropylthiocarbamate), EPTC (S-ethyl dipropylthiocarbamate), and butylate (S-ethyl diisobutylthiocarbamate). In the field, butylate + R-25788 (N₂N-diallyl-2,2-dichloroacetamide) and EPTC + R-25788 at 4.5 + 0.2 kg/ha provided good control (60 to 96%) of hemp dogbane during the first 2 months after corn (Zea mays L.) planting, but decreased to 0 to 40% at harvest. Higher rates of butylate + R-25788 controlled hemp dogbane slightly longer. Thiocarbamate herbicides inhibited deposition of epicuticular wax on the leaves of hemp dogbane in 1977 but not in 1978. It appears that preplant applications of the thiocarbamate herbicides may aid in controlling hemp dogbane via delayed emergence, reduced plant vigor, and possibly greater adsorption of 2,4-D applied subsequently as a foliar application.