abstract: The purpose of this work was to determine the influence of conventional and ploughless tillage systems on infestation in two differentiated fertilization and plant protection levels. Before harvest of winter rye, the weed infestation was determined with the square-frame method. The estimations included the number of weeds, the weed species composition and air dry mass of weeds in two random selected places of each plot (0.5 m2). Data obtained were statistically analysed by ANOVA, and the mean values were compared by means of the least significant differences using the Tukey test. Conventional tillage system compared with the ploughless system significantly decreased the number of monocotyledonous weeds, of total weeds, and air-dry mass of weeds. Conventional tillage system decreased primarily the appearance of Apera spica-venti in a canopy of winter rye. Intensive fertiliza-tion and plant protection significantly decreased the number of dicotyledonous weeds and total weeds in canopy of winter rye. Intensive mineral fertilization with Starane 250 WC (fluroxypyr), compared to the basic fertilization, notably limited the number of Matricaria maritima and the number of weeds species – from 38 to 32.