Weed control is a major constraint for organic production around the world. Field studies were conducted in pepper (Capsicum annuum L.) from 2004 to 2006 at the Black Sea Agricultural Research Institute experimental field ill Turkey to determine the weed Suppressive effects of winter cover crops. Treatments consisted of ryegrass (Lolium multiflorum L), oat (Avena sativa L.), rye (Secole cereale L.), wheat (Triticum aestivum L.), gelemen clover (Trifolium meneghinianum Clem.), Egyptian clover (Trifolium alexsandrinum L.), common vetch (Vicia sativa L.), hairy vetch (Vicia villosa Roth.) and a bare fallow with no cover crop. Weed density and total weed dry biomass were assessed at 14, 28, and 56 days after incorporation to quantify effects of cover crops during a Subsequent pepper crop. Cover crop establishment was similar in both growing seasons and individual Species produced ill the range of 18003500 kg/ha biomass. Ryegrass produced the greatest biomass compared with other species. Weed dry biomass production just before cover crop incorporation varied with year and cover crop species. Hairy vetch, ryegrass, oat and common vetch were the most competitive cover crops based on total weed dry biomass. Hairy vetch was the most promising cover crop and reduced weed density by 73% and 70% at 28 and 56 DAI, respectively. Pepper yields were higher following all cover crops except Egyptian clover. The highest yield was obtained from hairy vetch plots in both years. This research indicates that cover crops Such as hairy vetch, ryegrass, oat and common vetch could be used in integrated weed management programs to reduce weed infestation in organic pepper. (C) 2008 Elsevier Ltd. All rights reserved.