With the objective to study the effects of weed interf erence periods on some co m yield parameters, i t was settled two field trials with cultivars Cargill 606 and Agroceres 106, in a yellow-Red Latossol-distrofic, at Pira cicaba, são Paulo State, Brazil.It was also studied the integration of cult� ral practices with herbicides 2,4-D, atrazine + seed oil and bentazon applied in post-emergence doses rate and 75% of dose rate.For weed interference trials the experimental design used was the randomized blocks, where the cultivars were kept with and without weed competition in different period of time which were: O, 10, 20, 30, 40 and 50 days after crop emergence.For the integration cultural practices and doses reduction of herbicides trials, it was also used the randomized block design, wi th 16 treatments wi th four replic� tions, in one trial it was used 1,0 m row spacing and in the other, 0,80 m spacing, which were submetided to sta tistical analisys. Based on results the folloing conclusions may be drawn: la.) The presence of weed during all cycle of crop reduced fi nal height, grain yield, and weight of 100 grains. There were not significative differences with competition in the parameters of initial and stands of corn, ear height, diameter of macronutrientes. stem weed final and 2a.) The corn crop should be k ept free of weed interferen ce during the first 20 days after emergence for cv.Cargill 606 and Agroceres 106 to avoid loss of grain yield.3a.) The herbicides 2,4-D, atrazine + seed oil and benta zon did not affect the initial and final corn plants.These herbicides did not cause intoxication to corn plants, as well as, its did not _show significative differences to macronutrients and weight of 100 gra ins.4a.) The reduction of spacing did not increment weed con trol to a satisfactory level, although, in some casesxiii.were detected significative differences between the dose used and the crop spacing. Sa.) Digitaria horizontalis willd was not controled by 2,4-D and bentazon herbicides, although, atrazine + seed oil showed good control of this species. Sida rhombifolia L. was controled by 2,4-D and bentazon just with a rate dose, but atrazine + seed oil showed a good control on this species with rate dose and re duction dose. Blainvillea rhomboidea Cass. and Bi dens pilosa L. were controled by 2,4-D; atrazine + seed oil and bentazon herbicides. On the other hand, the weed Indigcfera hirsuta L. was controled by2,4-D and bentazon herbicides with rate doses, therefore, atrazine + seed oil showed good control of this weed in the doses that were applied. Ipomoea hederifolia L. was controled satisfactorily by 2,4-D and atrazine + seed oil in rate dose and your reduction. Bentazon controled Ipomoea hederifolia L. just in a rate dose.xiv.
