The purpose of this work was to determine the influence of conventional and ploughless tillage systems upon potato canopy infestation at two differentiated fertilization and plant protection levels on a light soil. Before closing of rows and before harvest of potato tubers the assessment of canopy infestation was made with quantitative-weighting method. The density of weed individuals were counted, the species composition and the air-dry of above-ground parts were estimated from randomly located sample areas of 150 cm x 33.4 cm in size at two sites on each plot. The obtained results were analysed statistically by means of variance analysis. The mean values were compared by means of Tukey`s test i.e. the smallest significant differences. Tillage systems did not differentiate significantly the number of weeds in potato canopy. Number of dicotyledonous weeds, monocotyledonous weeds, total weeds and dry matter of weeds was higher on objects with basic fertilization and plant protection level in comparison with the intensive ones. Conventional tillage system caused a decrease – before closing of rows and before tuber harvest – in the numbers of the following species of weeds: Galinsoga parviflora, Geranium pusillum, Poa annua and Agropyron repens. Intensive level of fertilization and plant protection decreased weed infestation first of all with respect to such species as Matricaria maritima, Chenopodium album and Echinochloa crus-galli in comparison with the basic treatments.