In experiments carried out in 2008–2009 the influence of soil tillage system and irrigation on weed infestation in yellow lupine was investigated. Soil tillage system significantly modified the number of weeds per unit area. More weeds and species of weeds were observed in direct seeding. Irrigation did not result in significant differences in the number of weeds but had a significant influence on air-dry mass of weeds in interaction with soil tillage system.