canola (brassica napus l.) - weeds interaction under different weeding time

in order to evaluate the impact of time of weed control on yield and yield components of two rapeseed cultivars (zarfam and opra) two separate experiments based on each cultivar conducted at shahryar (karaj). the experiment was carried out based on rcbd with three replications and six treatments for each cultivar. treatments were exerted on the different phenological growth stages including the emergence of 4th and 8th leaf, branching, flowering as well as weed-free and weed-infested stages in whole plant growth cycle. in current study some weed species including wild mustard (sinapis arvensis l.), wild oats (avena ludoviciana dur.), lambsquarter (chenopodium album l.), and hoary cress (cardaria draba (l.) desv.) were selected as main weed species based on their higher dry matter. in both cultivares extended weed interference resulted in increased weed total dry matter. weed interference in four-leafed, eight-leafed, branching, flowering, weed- free and total infestation sages in comparison with weed-free period led to 20، 33، 38، 50 and 55 percent reduction in grain yield respectively in zarfam cultivar whilst these figures were about 14, 25, 29, 48 and 56 percent in opra cultivar respectively. the results of mean comparisons revealed that in weed-free treatment, the highest number of sub-branches were 8 and 5/33 in both zarfam and opra respectively. among the weed-interference treatments the highest number of pods in zarfam cultivar was achieved at the four-leafed stage with 133 pods per plant but in opra cultivar the four-leafed, eight-leafed and branching stages have the highest number of pod per plant as 67/110, 67/109 and 33/108 receptively, which proved no significant difference. in both zarfam and opra varieties the highest number of grain per pod was observed in weed-free treatments which was equals to 26.67 and 21.33, respectively.