Biomass allocation on redroot pigweed (Amaranthus retroflexus) shoot at interference with three sunflower cultivars; Azarghol, Hysun and Allstar

In order to determination of effect of sunflower (Helianthus annus L.) cultivars on biomass allocation of redroot pigweed، a two years experiment was performed factorially based on additive design with sunflower cultivars (Azarghol، Hysun and Allstar)، redroot pigweed densities (8. 3، 25 and 41. 7 plants m-2) and relative times of weed emergence (emerged with sunflower; 15 and 30 days after sunflower emergence) in Tabriz. For combined analysis of data and means comparison MSTAT-C and Duncan''s test were employed. Results revealed that in Allstar treatments، number of weed side branches in densities of 25 and 41. 7 plants/m2 increased، significantly، compared with Hysun. In Allstar، redroot pigweed density was more effective than interference time with a view to effect on weed total biomass. Redroot pigweed leaf to total dry matter ratio in full season interference of 41. 7 weeds/m2 were 15%، 17. 5% and 20. 8% in three sunflower cultivars، respectively. With each week earlier emergence of weed، stem biomass of weed increased 6 g/m2، in Allstar. Florescence to total biomass ratio increased، significantly، with delaying in interference time of redroot pigweed، which could be considered in the weed controlling of sunflower.