response of rice and barnyardgrass (echinochloa crus-galli) to rate and time of application of some paddy herbicides

this study was carried out in 2008 and 2012 in rice research institute of iran (rasht) in order to study the response of barnyardgrass and rice to oxadiargyl (oxa), butachlor (buta) and thiobencarb (tb) herbicides. treatments included herbicide doses in six levels up to three times the recommended rate, and time of application in two levels before transplanting (bt), and after transplanting (at).results showed that herbicides efficacy on barnyardgrass control up to 4-wat was similar (≤ 95). oxa efficacy 6-wat decreased to 50-60%, but two other herbicides efficacy was similar to previous stage. herbicides phytotoxicity increased as herbicides dose increased, but differently between herbicides and time of application. oxa toxicity was less when applied bt compared with at application, while tb and buta, showed more toxicity if applied bt. day to 50% flowering increased as herbicides doses increased, but the slope of linear fitted model was twice more for tb if applied bt compared with at application and also in comparison with two other herbicides.