The mechanical weed control with a flex tine harrow applied to winter cereals crops can be an adequate alternative to the herbicide use in winter cereals in some situations. To study the flex-tine harrow performance five experiments comparing different mechanical regulations for weed control, crop damage and barley production were developed. Number of tillages, their depth, direction, speed and time of tillage were the studied variables. The harrow efficiency was very low against grass weeds (Lolium rigidum, Avena spp.), perennials (Rumex crispus) and, generally, when plants surpassed the seedling stage. Efficiency against dicot weeds was higher in seedling stage when increasing the depth, speed and number of tillings, the work was carried out parallel to crop rows. However a higher control did not mean higher crop yield. Hence only one tillage at normal or high depth, along the tillering cereal rows at 9 km/h speed. Obtained the best efficiency/crop damage relation and higher yield.