The aim of the paper was to determine the influence of fertilizing on the infestation of winter leek varieties of Bartek and Arkansas with Napomyza gymnostoma (Diptera, Agromyzidae). The field test was performed by random blocks in four repetitions: I - caw manure vermicompost, II - beet pulp vermicompost, III - mineral fertilizing, IV - control without fertilizing. As a result of the conducted tests it was proved that vermicompost fertilizing did not have an essential effect on the healthiness of the tested leeks.