Response of morphological traits, yield and harvest index of three winter rapeseed (Brassica napus L.) cultivars to different times of weeds control

An experiment was conducted to study the effects of weeds (Sinapis arvensis, Hordeum spp., Secale montanum and Agrostemma githago) competition on morphological traits, yield and harvest index of three winter rapeseed (Brassica napus L.) cultivars at Islamic Azad University of Tabriz, Iran during 2008. Studied factors were weed control time included weeding in rosette, early stem elongation, early flowering and 50% flowering stages, full season competition, control and SLM046, Opera and Okapi cultivars. Results showed that number of branches per plant were 4 and 2 in control and full-season interference treatments, respectively. Biological yield of rapeseed in whole season weed-infested plots reduced 40%, as compared with control. Weeds biomass in treatments those weeds were controlled at early stem elongation, early flowering and 50% flowering stages had no-significant difference. Weeds could increase biomass up to 410 g m-2 when grew with rapeseed along the season. Weeds control had significant difference with weed-free plots in early stem elongation, early flowering and 50% flowering stages with 32%, 44% and 50% reduction value in seed yield, respectively. When the weeds competition period took a long time, seeds weight decreased. Seed oil percentage was not affected by cultivars and weeds competition periods. Reduction value in oil yield of rapeseed in different levels of weed control were 32%, 4%, 45%, 50% and 55%, respectively.