INFLUENCE OF APPLICATION VARIABLES ON EFFICACY OF GLYPHOSATE

Field experiments were conducted from 1993 to 1995 to compare weed con trol by the isopropylamine salt of glyphosate at 0.21, 0.42, 0.63, and 0.84 kg ae/ha applied at three stages of weed growth. Weed control by glyphosate applied at these rates alone or with ammonium sulfate at 2 .8 kg/ha was also evaluated. In other experiments, potential interacti ons between glyphosate and acifluorfen, chlorimuron, and 2,4-DB were e valuated. Velvetleaf, prickly sida, sicklepod, pitted morningglory, en tireleaf morningglory, palmleaf morningglory, and hemp sesbania were c ontrolled more easily when weeds had one to three leaves compared with control when weeds had four or more leaves. Glyphosate controlled red root pigweed, velvetleaf, prickly sida, sicklepod, and barnyardgrass m ore effectively than pitted morningglory, entireleaf morningglory, pal mleaf morningglory, or hemp sesbania. Increasing the rate of glyphosat e increased control, especially when glyphosate was applied to larger weeds. Greater variation in control was noted for pitted morningglory, palmleaf morningglory, prickly sida, and velvetleaf than for redroot pigweed, sicklepod, entireleaf morningglory, or hemp sesbania. Ammoniu m sulfate increased prickly sida and entireleaf morningglory control b ut did not influence sicklepod, hemp sesbania, or barnyardgrass contro l. Acifluorfen applied 3 d before glyphosate or in a mixture with glyp hosate reduced barnyardgrass control compared with glyphosate applied alone. Chlorimuron did not reduce efficacy. Mixtures of glyphosate and 2,4-DB controlled sicklepod, entireleaf morningglory, and barnyardgra ss similar to glyphosate alone.