The aim of the research was comparison of the effect of tillage system (ploughing or conservation) and various catch crops and air dry matter produced by them on the level of weed infestation of spring wheat canopy cultivated after itself. The research was carried out in the years 2006-2008 on medium heavy mixed rendzina soil. The static two-factorial experiment included ploughing tillage (A) and conservation tillage with autumn disking of catch crops (B) or with their spring disking (C). At the same time, four methods of stand regeneration were applied in spring wheat monoculture in the form of various catch crops. With reference to the control plot without catch crops (a), effect of undersown catch crops of red clover (b) was compared with westerwold ryegrass (c), as well as stubble catch crops of lacy phacelia (d) and white mustard (e) on the level of weed infestation of spring wheat canopy. Conservation tillage increased species diversity of weeds in the canopy of spring wheat, their total number and air dry mass compared with the ploughing tillage. Introduction of catch crops in the spring wheat monoculture decreased species diversity in segetal flora compared with the control plot (without catch crops). Undersown catch crops of red clover and westerwold ryegrass produced a greater biomass in the evaluated 3-year period, and reduced the number of weeds to a greater extent than stubble catch crops of lacy phacelia and white mustard. Air dry mass of weeds in spring wheat cultivated after undersown catch crop of red clover was significantly lower than after undersown catch crop of westerwold ryegrass. The species that occurred in greatest numbers in the spring wheat canopy were: Galium aparine, Fallopia convolvulus and Avena fatua. Tillage system had no significant effect on the yield of dry matter of catch crop plants. Undersown catch crops reacted to changeable weather conditions to a lesser degree than stubble catch crops.

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