There is currently a very favorable climate for biological control of pest weeds. Moreover, biological control plays a significant role in the Integrated Plant Protection Management. Traditional methods of weed control, such as cultivation and the use of herbicides are not practical or desirable for some stands of weeds, and biological control has become an attractive strategy for control of pest weeds. Control of Rumex confertus Willd. by natural enemies that reduce its density is the good example of utilizing biological control on the European and worldwide scale. The aim of the conducted studies was to evaluate the dynamic of population of Pegomya nigritarsis Ztt. (Diptera, Anthomyiidae) on Rumex confertus Willd. and to determine the impact of pest's injuries on the growth of a plant.