To evaluate the effects of different adjuvants on bentazon herbicides' efficiency in conjunction with planting density on broad-leaf weeds control and linseed (flaxseed) crop yield and yield components, an experiment was conducted during the agronomic year of 2011 in Isfahan University of Technology's research field. This experiment was carried out as a factorial in a completely randomized block design in three replications. Experimental treatments included two levels of linseed planting density (400 and 700 plants per square meter), three levels of bentazon herbicide dose (0.96, 1.20 and 1.44 kg active ingredient ha -1 ) and five adjuvant factors ( without adjuvant, ammonium sulfate (2% w/v), nonionic surfactant of Tween 20 (0.25% v/v), soybean oil (vegetable oil, 1.25v/v) and anionic surfactant (alkyl ether sulfate sodium salt) (0.5%v/v) ) . Results indicated that a planting density of 700 plants per square meter resulted in more favorable linseed and weed traits than a density of 400 plants per square meter. Higher bentazon herbicide dose mixed with adjuvants increased herbicide efficiency as the total number broad-leaf weeds was reduced, and yield, branch numbers and capsule numbers per plant were increased, Although there was no significant difference between bentazon doses of 1.2 and 1.44 kg active ingredient ha -1 . Additionally, adjuvants of ammonium sulfate were the most efficient, and detergent liquids and non-adjuvants were the least. As the herbicide dose was increased, linseed phytotoxicity was intensified. The lowest phytotoxicity occurred in the presence of 2% ammonium sulfate and the detergent effect it caused (47%). The plant growing period was prolonged as a result of high plant density, weed competition and phtotoxicity, leading to a significant reduction in yield. This result may be due to the synchronizing of linseed ripening with warmer temperatures during the plant growth period, which increased the percentage of linseed oil. Application of bentazon with ammonium sulfate allowed a 17% reduction in herbicide dose application while achieving acceptable weed control. The results of this study suggest that a planting density of 700 plants per square meter and application of 1.2 kg/active ingredient ha -1 of bentazon herbicide is desirable to control broad-leaf weeds in linseed. Among the tested adjuvants, ammonium sulfate with herbicide additives gave better results than the other adjuvants. This may be due to a reduced antagonistic effect in hard water of EC and pH adjustment.
