Three year research (2008/09-2011) at the lessive soil of the Eastern Croatia near town Valpovo has been conducted in order to establish the impact of winter cover crop treatments at weed population between soybean harvest and seeding of the popcorn maize (Zea mays everta Sturt.) crop, weed in popcorn maize crop, as well as growth, development, yield and yield components of the popcorn maize as the main crop. The research has been conducted in accordance with organic rules, and it has been set up as complete randomized block design in four repetitions with 12 cover crop treatments: N-control, no cover crop, single cover crops: R-winter rye, P-winter wheat, F-phacelia, Sg-fodder pea, Vic-hairy vetch; and cover crop mixtures: RSg, RVic, PSg, PVic, FSg and FVic. Dominant weed species determined in this trial were: Matricaria chamomilla L. and Arabidopsis thaliana L. found in winter cover crops, and Ambrosia artemisiifolia L., Chenopodium album L., Amaranthus retroflexus L., Echinochloa crus–galli (L.) PB. and Setaria glauca (L.) PB. in popcorn maize. The least weeded were cover crop mixtures PSg, RVic and PVic and single cover crops R, Vic and P, with significantly lower number of weed in comparison with the control. Treatments with the highest shoot production were RVic, RSg, R and P. Weather did influence significantly weedeness, especially in very moist period of the year 2010. The weedness in popcorn maize, in comparison with control, was higher at treatment P, main crop density was not affected by cover crop treatments, whereas height of the popcorn maize was lower at treatments R and FVic. The highest popcorn maize grain yield was recorded at PVic treatment in 2010 (2.5 t ha-1), whereas, in average, higher yields, in comparison with control, were recorded at PVic and FVic treatments. Treatment Sg had the highest average hectolitre weight and 1000 grains weight in comparison with control. The mixtures of cereals and legumes were proven to be more effective in weed suppresion in comparison with single cover crop treatments, whereas treatments PSg, RVic and RSg can be recommended as the most effective in weedness control.