Control of Quackgrass (Agropyron repens) in Soybeans (Glycine max) with HOE 29152

Abstract

In field studies, postemergence applications of HOE 29152 {2-[4-(trifluoromethyl phenoxy)phenoxy] propanoate} at rates of 1.68 to 3.36 kg/ha effectively controlled quackgrass [Agropyron repens(L.) Beauv.] when applied to plants in the one- to three-leaf stage. Control was still effective the following year. The addition of a surfactant to HOE 29152 did not increase quackgrass control, but it did increase soybean [Glycine max(L.) Merr.] injury. Cultivation 1 or 7 days after herbicide application increased the efficacy of HOE 29152 on quackgrass. Due to abundant moisture in 1977, untreated quackgrass-infested plots yielded as much as the weed-free plots. However, in 1976, a very dry year, the control of quackgrass with HOE 29152 resulted in greatly increased soybean yields. In greenhouse studies, postemergence applications of HOE 29152 at rates of 0.56 to 3.36 kg/ha effectively killed rhizome buds and reduced shoot dry weights of quackgrass. The phytotoxicity of HOE 29152 at 0.56 kg/ha was less at a postspray temperature of 36 C than at 17 or 27 C; however, the phytotoxicity of HOE 29152 at rates of 1.68 and 3.36 kg/ha was similar at all three temperatures. HOE 29152 can volatilize from soybean leaves, with volatility greater at 38 C than at 21 C. Postemergence applications injured soybeans similarly in field and growth chamber studies. Injury was observed only on leaves that were expanded at time of treatment, was short-term, and was most prevalent at 3.36 kg/ha.