Understanding of weed-crop interactions is needed for the development of integrated weed management systems. A field study was conducted to evaluate an existing model to predict corn yield loss as a function of different time of weed emergence and removal. The treatments were consisted of two different periods of weed interference at different stages of corn development using a randomized complete block design with 12 treatments and 3 replications. The data sets were analysed by a Gompertz nonlinear function. The results of this trial approved that model was robust enough to predict yield loss caused by a mixed weed infestation with a single set of parameters. In term of critical period of weed control, outcomes of the model showed that on the basis of 5% acceptable yield loss this period was 21-98 days after sowing and with 10% acceptable yield loss this period was 44-76 days after sowing. It reveals that corn is able to tolerate early weed competition. Therefore, weed control management strategies can be postponed till 21 or 44 days after sowing on the basis of 5 and 10% acceptable yield loss, respectively. For that reason, pre-emergence treatments are unnecessary. However, it is necessary to protect corn from weeds for a long time to prevent high yield loss.