It was tested the effects, in a medium term, of four methods to control undesirable plants on forage production and dynamic of vegetation in a representative area of natural pasture in the transition between Serra do Sudeste and the Depressão Central in Rio Grande do Sul. The control methods were the following: without control, mechanical control with spring mowing, mechanical control with autumn mowing and chemical control with Tordon commercial herbicide based on Picloram + 2,4-D at the dosage 5 L/ha associated or not with the fertilization system (with and without fertilizer). There was an interaction between fertilization system and season of the year and interaction between the control method and season of the year for available forage and grass mass. The fertilization system improved the available forage [4,919.0 kg/ha of dry matter (DM)] and mass of grasses (2,313.1 kg/ha of DM). Forage mass was higher in the absence of undesirable plant control, which resulted in values 5,024.4, 3,931.3, 3,020.1 and 3,701.1 kg/ha of DM in the summer, winter, autumn and spring, respectively. The frequency of undesirable species is not modified by fertilization (8.0% without fertilizer and 8.4% with fertilizer). Chemical control promotes total control of undesirable species and native leguminous. Autumn mowing is more efficient in controlling undesirable species than spring mowing.
