WEED-CONTROL IN SOYBEAN (GLYCINE-MAX) WITH IMAZAMOX AND IMAZETHAPYR

Field and greenhouse experiments were conducted in 1995 and 1996 to de termine soybean injury and weed control differences from imazamox and imazethapyr applied postemergence with a nonionic surfactant or methyl ated seed oil and with selected tank mixtures. Soybean injury from ima zamox at 35 g ai ha(-1) plus either a methylated seed oil or nonionic surfactant was equal to injury from imazethapyr at 70 g ai ha(-1) in t he greenhouse and field. Imazamox provided greater common lambsquarter s control than imazethapyr in the field in 1995 and in the greenhouse. Thifensulfuron tank mixed with imazethapyr increased common lambsquar ters control, while soybean response increased when thifensulfuron was tank mixed with imazamox. Common ragweed dry weight was reduced 61% t o 64% from 35 g ha(-1) imazamox and 70 g ha(-1) imazethapyr in the fie ld; however, imazamox provided greater common ragweed control than ima zethapyr in the greenhouse. Tank mixtures of lactofen with imazamox or imazethapyr increased common ragweed control and resulted in greater soybean seed yield in 1996 than when imazamox and imazethapyr were app lied alone; however, lactofen antagonized giant foxtail control with i mazamox and imazethapyr, and antagonized common lambsquarters control with imazamox. Giant foxtail control in the greenhouse was antagonized more when acifluorfen, fomesafen, and lactofen were tank mixed with 3 5 g ha(-1) imazethapyr than with 35 g ha(-1) imazamox. Giant foxtail c ontrol with imazamox or imazethapyr applied alone or with diphenyl eth er herbicides increased when 28% urea ammonium nitrate was added with nonionic surfactant compared with nonionic surfactant only. Ima zethap yr antagonized giant foxtail control by clethodim in the field and was more antagonistic than imazamox in the greenhouse. A methylated seed oil improved common ragweed control by imazethapyr at 70 g ha(-1) and imazamox at 18 and 35 g ha(-1), while common lambsquarters and velvetl eaf control increased when a methylated seed oil was included with 18 g ha(-1) imazethapyr compared to nonionic surfactant in the greenhouse .