Weeds can reduce yield, which justify the need for their efficient management. The stage that precedes the management consists of identifying the species present in the area, and then making the decision of the best method of control. Thus, this study aimed to perform a phytosociological survey, and to analyze the composition and floristic similarity of weeds between the end of the corn crop cycle and in the off-season period. The authors analyzed nine areas representing the second crop corn and six in the off-season period, distributed in four municipalities: Francisco Alves, Marechal Cândido Rondon, Palotina and Terra Roxa. For estimation of weed species, the square inventory technique of 1 m2 was used. The sampling design consisted of three collection ranges, the first starting at 5 m from the edge, followed by 25 and 50 m inside the crop. In the second crop corn, 29 species grouped into 17 families, in the off-season period, and 35 species grouped into 18 families were recorded. Parietaria spp. and Conyza spp. stood out as main species in areas occupied by second crop corn and Parietaria spp. and Gnaphalium spicatum Lam. in areas of the off-season period and inside sampling range of this period. The similarity index evidenced a high similarity between the periods sampled.
Key words: Weeds, identification, importance value, density.