The objective of this work was to evaluate the efficiency of the mechanical method of weed control in sorghum crop, and to determine the critical period of competition between weeds and the culture under lowland fields in temperate climate areas, considering the development stage of the sorghum plants. The trial was installed under field conditions, in lowland where flooded rice had grown in the previous five years, with high infestation levels of barnyardgrass (Echinochloa sp.) and alexandergrass (Brachiaria plantaginea). The treatments were intercropping periods or absence of weeds in the experimental unitis. These periods were from emergence until the crop stage of 3, 5, 7 or 9 completely expanded leaves. Besides the treatments that involved the presence or absence of weeds, there were one control always free of infestation and one with no weed control. It was concluded that weed control in the sorghum crop, grown in lowland fields of temperate climate areas, should be conducted between the emission of the third and the seventh leaves of the crop, with the adoption of mechanical control being viable for this objective, with no damage for the sorghum grain yield.
red rice; barnyardgrass; competition
