The handling of the harmful plants is essential for the development of the soy and can be made through diverse methods. It is of basic importance the knowledge of the appropriate period for the accomplishment of this handling, that is, the period which the presence of harmful plants will cause posterior damages (MELO, 2001). The possibilities of handling of the harmful plants in the culture of the soy are diverse. The different forms of handling can more be used separately or in combination of two or, aiming at to the effectiveness, economicidade and praticidade (LEATHER STRAP; REZENDE, 2008). Preventive handling involves the use of pure seeds and programs of reduction of seeds of harmful plants in the period between harvests, by means of practical diverse and of the rotation of cultures.
Cultural handling is made by means of the choice to cultivate, of the population handling and practical fitotcnicas. Mechanized handling is viable economically, since that it has adjusted sizing between the area, to cultivate, the size and the income of the used equipment. Biological handling, in the culture of the soy is associated with the handling chemistry. Chemical handling is used in the culture of the soy, the applications of herbicidas can be made before the sowing, with the incorporation to the ground (PSI) only in the conventional system of sowing; after the sowing, but before the emergency of harmful plants (DAILY PAY) e, after the emergency of the harmful plants and the culture (AFTER) (FERRI; ELTZ; KRUSE, 1998). In the conventional system, the control of the harmful plants before the sowing of a culture is effected by mechanical operations (arao and gradagens), to the step that, in the direct sowing, by the no-revolvimento of the ground, the harmful plants gifts are eliminated by means of the desiccant herbicidas. The expenditures with herbicidas are bigger in the system of direct sowing of what in the conventional; however, the expenditures with the agricultural operations are substantially bigger in the conventional system.