This work evaluated the weed control in glyphosate tolerant soybean crop without additional management practices. Two experiments were carried out under field conditions in the agricultural years 2006/2007 and 2007/2008 in Jaboticabal, São Paulo State, Brazil. It was tested two glyphosate-tolerant varieties (CD 214 RR and M-SOY 8008 RR), eight herbicide treatments (Roundup Ready, single spraying at rates of 0.48; 0.72; 0.96 and 1.20 kg ha-1 of glyphosate acid equivalent, associates or not to sequential spraying at 0.48 kg ha-1), and two controls (one under mechanical control and one untreated control). Soybean varieties influenced the infestation of weed species. Xanthium strumarium was predominant in control treatments, reducing the occurrence of other weeds species. Independently of the dose, glyphosate sprayings resulted in low infestations 35 and 40 days after the first spraying, in the first and second year, respectively. The weed control in transgenic soybean is directly influenced for the glyphosate rate, having satisfactory control with the single application at 0.96 kg ha-1 or sequential at 0.48 plus 0.48 kg ha-1 of glyphosate. Under lesser infestation conditions (2006/2007), the single application at 0.48 kg ha-1 of glyphosate is enough for weed control. The varieties of transgenic soybean CD 214 RR and M-SOY 8008 RR distinguishing influence the dynamics of the weed species. The chemical control is more effective in the M-SOY 8008 RR, where it had minor diversity and development of the weed.
Chemical control; transgenic soybean; Xanthium strumarium
