To estimate the yield losses due to interference of weeds is an important aspect for timely weed management. In view of this, two additive design experiments were conducted during rabi seasons and planted in November 2012 and subsequently repeated in 2013 to investigate the potential of various densities of Avena fatua and Rumex dentatus on the total biomass and yield of wheat in Dera Ismail Khan; the extreme southern district of Khyber Pakhtunkhwa, Pakistan.  Randomized complete block design was used in both the experiments, by maintaining the density of A. fatua and R. dentatus in nine treatments (0, 5, 10, 15, 20, 25, 30, 35, 40 seeds m^-2) and three replications. The seed rate of wheat was 125 kg ha^-1. The results of each experiment indicated that the increasing densities of both A. fatua and R. dentatus severely decreased the wheat grain yield by 78 and 60 % and total dry matter yield by 80 and 74 % by A. fatua and R. dentatus, respectively as compared to control treatments. Furthermore, compared with lower densities of the weed species, the biomass of both A. fatua and R. dentatus was higher in the treatment having maximum density (40 plants m^-2). It can be concluded from these studies that the uncontrolled population of A. fatua and R. dentatus can cause severe reduction in wheat yield. Moreover, this study will facilitate the farmers and scientists to determine the threshold levels and competition indices of A. fatua and R. dentatus and other major weeds that cause yield reduction in wheat crop.