A field experiment was carried out at Boa Terra Farm (Quarto Centenário, PR) ,to evaluate the effect of different periods of Euphorbia heterophylla interference on low-density soybean (cv. BRS-133). The experiment was carried out in a randomized complete block design, with four replicates and 11 periods of weed interference, by using twofold checks. The periods of interference consisted in keeping the weed interference for 5, 12, 19, 26, 33, 40, 47, 54, 61, 68 days after crop emergence (DAE) or for the whole cycle. At the first weeding, E. heterophylla densities and dry mass were analyzed. Crop stand and yield were the parameters that expressed the most damages due to the increased weed interference period. Using twofold checks, the period before interference was 11 days after emergence (DAE), indicating the need of early weed control. From the 11th to the 68th DAE, the interference imposed by weeds promoted daily losses of 6.45 kg ha-1 in soybean yield. Weed competition for the entire cycle promoted a 38% decrease in crop yield.
competition; Euphorbia heterophylla; two-fold checks
