Cover cropping in fallow period brings many benefits in organic farming and weed suppression is one of the possible effect. The main aim of this two year research (2008/09-2010) was to determine the influence of winter cover crops incorporation on weediness in organic popcorn (Zea mays everta Sturt) production. The field trial was set up at the lessive soil of the Eastern Croatia (45°38' 46, 52'' N / 18°23' 32, 73'' E) as complete randomized block design in four repetitions. The five cover crops treatments were used: Wr – winter rye, Ww – winter wheat and V - hairy vetch, as single crops, and cover crops mixtures WrV and WwV. Fallow area was used as a control: Z (zero). Sampling to quantify the dry matter and incorporation of cover crops were performed just before full flowering period of cover crops and the popcorn maize was sown right after. Dominant weed species determined in this trial were Ambrosia artemisiifolia L., Amaranthus retroflexus L., Echinochloa crus – galli (L.) PB. and Setaria glauca (L.) PB. Treatments with the highest shoot production were Wr and WrV. The weediness in popcorn maize was higher at winter cover crops treatments compared to control. Looking at winter cover crops treatments only, the least weeded was WwV mixture regarding total weed number, and V and Wr treatment showed the lowest weed height, whereas height of the popcorn maize was the lowest at Wr treatment. The highest weed aboveground biomass was recorded on WrV treatment. Results of this experiment indicate the increasing of weed infestation caused by winter cover crops incorporation.