Introduction the productive potential of the cultures depends, among others factors, of the intensity, the time and the infestation of of spontaneous plants. The control is necessary since the same ones compete with the cultures for essential factors for its development, as water, light and nutrients. Beyond serving of shelter for insects, patgenos of illnesses and nematides, and making it difficult or to make impracticable its harvest. This interference of the spontaneous plants results in qualitative and quantitative damages to agricultural production (FERRI; VIDAL, 2003). The occurrence of spontaneous plants since the beginning of the cycle of the cultures can generate accented losses of productivity, mainly if the control of these plants inefficient or will be carried through at inadequate time (FERRI; VIDAL, 2003). One becomes necessary to use differentiated manejos e, preferential, integrated, being essential to know the characteristics of the commercial culture and the infestantes plants, as well as the critical periods of convivncia between same and the caused economic damages, to get a bigger efficiency in the handling system. The factors that influence the degree of interference of a infestante plant in a culture can be related the infestante community (specific composition, density and distribution), to the culture (espaamento, density and cultivate) and to the environment (alone, adopted climate and practical of handling). In this interactive process, the factors more easily controlable, in the practical one, are the time and the extension of the period of convivncia between the harmful culture and plants. As for the time where the infestantes species compete for the factors of growth with the cultivated plants, the initial period of more important competition englobe first the 25 33% of the vegetative cycle of the cultures, because in this phase not yet it even has good covering of the ground for the majority of the cultivated plants (MELO et al., 2001). Of all the factors that influence the interference degree, most important are, perhaps, the period where the infestante community and the cultivated plants are disputing the resources of the way.