Control of Annual Morningglories (Ipomoeaspp.) in Soybeans (Glycine max)

Abstract

Field studies were conducted in North Carolina in 1981 and 1982 to evaluate the efficacy of postemergence over-the-top and postemergence-directed herbicides for control of five morningglory species: entireleaf [Ipomoea hederacea(L.) Jacq. var.integriusculaGray], tall [Ipomoea purpurea(L.) Roth. ♯3PHBPU], ivyleaf [Ipomoea hederacea(L.) Jacq. var.hederacea♯IPOHE], pitted [Ipomoea lacunosa(L.) ♯ IPOLA], and scarlet [Ipomoea coccinea(L.) ♯IPOCC]. The glabrous morningglories (scarlet and pitted) were more easily controlled than the pubescent morningglories (ivyleaf, tall, and entireleaf). Lower soybean injury, higher morningglory control, and greater soybean seed yields were obtained with over-the-top herbicide applications at 4 weeks after planting (WAP) than at 6 WAP. Pitted morningglory was tolerant to low rates of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. This herbicide applied over the top at the R1 stage of soybean growth produced low yields, probably as a result of morningglory interference and herbicide injury to the soybeans. Postemergence-directed applications of linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and metribuzin [4-amino-6-tert-butyl-3-(methylthio-as-triazin-5(4H)-one] alone or in tank mixtures with 2,4-DB resulted in soybean injury that ranged from 12 to 36%. Highest soybean seed yields (equivalent to weed-free control) from postemergence-directed herbicides were obtained with applications of 2,4-DB, linuron, and a tank mixture of metribuzin and 2,4-DB.