Since its introduction in Brazil, she has been lead with high level technician in all its operations, exactly thus, this it subjects to a series of factors that can influence its development and its production (BORTOLUZZI; ELTZ, 2001). The presence of harmful plants in the culture is one of the factors that cause problems that if they reflect in losses in the product quality, the income and even though in the inviabilizao of the harvest. Some published works, based in world-wide averages, point out the harmful plants as the responsible greaters for the decline of production of the soy, in comparison with attacks of plagues and patgenos. The averages of the world-wide losses of production of soy grains, per year, due to occurrence of harmful plants are of 13%, while those decurrent ones of attack of plagues and illnesses is of 5 and 11% (OAK; VELINI, 2001). In relation to the production costs, the control of the invaders represents one of the item that more burden the producer, varying since 15% up to 40% of the total used with insumos. This percentile one shows the magnitude of the importance of the handling of the harmful plants in the culture and indicates the necessity to study adjusted techniques to minimize production cost and to reduce the aggression to the environment for the use of herbicidas..