| Resumo: |
There is little information about the precise dose of different herbicides for weeds in fallows. Herbicide efficacy varies for each weed species and plant size. The effect of glyphosate, 2,4-D, and metsulfuron-methyl + dicamba doses on biomass control of annual and perennial weed species at the vegetative and reproductive stage present in the autumn-winter-spring fallow in the soybean central region of Argentina was studied. Experiments were conducted in pots in 2003 and 2004. At the vegetative and reproductive stages, glyphosate, 2,4-D, metsulfuron-methyl + dicamba in three doses (2X, 1X, 1/2X) were applied; 1X being the recommended dose: 1440 g a.i./ha for glyphosate, 800 g a.i./ha for 2,4-D and 5.4 + 48 g a.i./ha for metsulfuron-methyl + dicamba. A control or check without application was included in the experiment. Thirty days after application, plant biomass was determined for each treatment in relation to the check. For all herbicides many species were adequately controlled with 2X but control was unsatisfactory for most species with 1⁄2X. Control at the vegetative stage was higher or similar to control at the reproductive stage. Perennial species were difficult to control with all herbicides.
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