Field experiment was conducted at Iranian Plant Protection Research farm in karaj during 2009 to evaluate the effects of diffrent planting patterns, times of mechanical control and herbicides application on weeds density and biomass in sugar beet farms. The experimental design was split–split plot based on randomized complete block design (RCBD) with four replications. Planting pattern considered as main–plot in three levels including single row planting with 50 cm row width, single row planting with 60 cm row width and twin row planting with 60 cm row width, time of mechanical control in three levels as sub–plot including mechanical weed control at 4–6 leaves stage, 10–12 leaves stage and 14–16 leaves stage (of sugar beet), and herbicides as sub–sub plot in two levels including metamitron plus combination of phenmedipham + desmedipham + ethofumesat and triflusulfuron–metil plus combination of phenmedipham + desmedipham + ethofumesat. Results of this study showed that times of mechanical weed control and herbicide application had significant effect on density and biomass of weeds. In most cases, planting pattern had appropiriate effect on weeds biomass reducthion that best results were achived in twin row planting 60 cm. Furthermore, Best results were achived in mechanical weed control at 4–6 leaves stage of sugar beet that had the most reduction on weeds density and biomass. metamitron plus combination of phenmedipham + desmedipham + ethofumesat had also the best effect on weeds density and biomass. Finally, sugar beet yield components were not affected by treatments as appropiriate as weeds control.
