Cumulation of dry matter in aboveground parts of sunflower at interference with redroot pigweed (Amaranthus retroflexus L.)

In order to quantify of dry matter accumulation in sunflower (Helianthus annus L.) at interference with redroot pigweed, a two years experiment based on additive design was performed factorially with sunflower cultivars (Azarghol, Hysun and Allstar), redroot pigweed densities (8.3, 25 and 41.7 plants m-2) at relative times of weed emergence (emerged with sunflower; 15 and 30 days after sunflower emergence) in Tabriz. Results showed that with increasing of 33.4 weeds/m2, biological yield of sunflower in three cultivars increased 40, 65 and 73 g/m2, when redroot pigweed emerged with sunflower. Effect of weed density unit on leaf dry matter in low densities was higher than high densities. Leaf to total dry matter ratio was not affected by studied treatments. The Azarghol can tolerate 8.3 weeds/m2 at 30 days after emergence without significant reduction in stem dry matter, while, reduction amount in two other cultivars were significant. In three cultivars, with increasing of weed density and earlier emergence times, anthodium dry matter reduced.