Organic sugar beet cultivation has gained in importance in Germany since conventionally produced sugar is no longer permitted to be added to organic products. Profitability of organic sugar beet cultivation depends primarily on the efficacy of weed control. During early growth stages the soil is partly uncovered over a period of time, thus providing favourable conditions for the development of weeds that can reduce growth and yield of sugar beet. The effects of timing of mouldboard ploughing and sowing, of mechanical and thermal weed control prior to emergence of the sugar beet seedlings, and spring tine harrowing the sugar beet crop were compared in on-farm trials. These on-farm trials were carried out in 2003 on a loessial soil near Goettingen which was shifted to organic agriculture recently. Weed density was determined on May 15th and was highest (110 weeds m-2) in the treatment with ploughing in autumn and early sowing (7th April). Ploughing in autumn and late sowing (April 22nd, with an additional pass for seedbed preparation) resulted in the lowest weed density (15 weeds m-2). 35 weeds m-2 were counted in the spring ploughing and late sowing treatment. In the treatment with autumn ploughing and early sowing Matricaria sp. were the main weeds whereas Chenopodium album L. dominated in the late sowing treatments. Spring tine harrowing and flaming prior to emergence of the sugar beets as well as spring tine harrowing in the 8 leaf stage of sugar beet had no effect on weed infestation.