The studies were carried out in the years 2009-2011 on medium heavy mixed rendzina soil. The aim of the study was comparison of the effect of tillage system and different types of catch crops on the weed infestation level in spring wheat canopy sown in monoculture. The experiment included plough tillage and conservation tillage with autumn and spring disking of catch crops. Four methods of plot regeneration were used in a form of various catch crops. With reference to the control without catch crops, effects of undersown red clover and Dutch ryegrass were compared, as well as of stubble crops of lacy phacelia and white mustard on the weed infestation of spring wheat canopy. Based on the conducted research it was indicated that plough tillage compared with conservation tillage decreased a number of dicotyledonous and monocotyledonous weeds, the total number of weeds and their air dry mass in the spring wheat canopy. Under conservation tillage, compared with plough tillage, there was a higher occurrence of Avena fatua and Cirsium arvense. Greater species diversity in weeds was observed on plots with conservation tillage. A lower number of monocotyledonous weeds was observed on the plot after stubble crop of white mustard, compared with the control plots where no catch crops were sown. Incorporation of both stubble crops and undersown red clover decreased dry weight of weeds in a spring wheat canopy, both compared with the control and with the plot after undersown grass. On plots after undersown red clover and Dutch ryegrass, a higher number of weed species was observed in the spring wheat canopy, compared with the control without catch crops. Conservation tillage promoted obtaining a higher biomass of catch crops than plough tillage. Undersown red clover produced a significantly lower biomass than stubble crops or undersown Dutch ryegrass.

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