In experiments to control weeds in corn, conducted on purple latosol soil, of the Chapadão series, three herbicides (Atrazine, Lorox and Ramrod) were compared, by applying them individually or in mixtures, in various doses and at different stages of the culture. As pre-emergent treatment, Atrazine was the most efficient in controlling annual broad leaf weeds. Lorox and Atrazine had a moderate action in the control of monocotyledonous weeds. The combination Lorox and Ramrod (1 kg/ha + 2 kg/ha) was the most promising in the reduction of grass weed species. The treatment Lorox + Atrazine (1 kg/ha + 1 kg/ha), in direct application, post-emergent in regard to corn and pre-emergent in regard to weeds, was the most satisfactory, in particular in the control of dicotyledonous weeds. This was the most long-lasting control of weeds. However, the same treatment Lorox + Atrazine, in broadcast application, post-emergent for the corn and for the weeds, was harmful for the corn crop.