Study of redroot pigweed (Amaranthus retroflexus L.) phenologic stages at interference with three sunflower hybrids

In order to study of redroot pigweed (Amaranthus retroflexus L.) phenology at interference with three sunflower, Helianthus annus L., cultivars, two field experiments were conducted during 005-006. Factorial experiments were established on randomized complete block design with three replications. Treatments were combination of three different weed densities (8., 5 and 4.7 plants m-) at three relative times of weed emergence (emerged with sunflower, 5 and 0 days after sunflower emergence) using three different sunflower cultivars (Azarghol, Hysun and Allstar RM). Analysis of variance revealed that the year effect was not significant. Redroot pigweed leaf number in each plant decreased significantly, by increasing weed density and delaying of weed emergence time. Sunflower cultivars also indicated different reactions. In redroot pigweeds that emerging with sunflower, branching at densities of 5, 5 and 5 plants/ m- of row delayed 0.67, 0. and days in Azarghol,. 68,. and 4. days in Hysun, in comparison with emergence at 5 days after sunflower, and delaying in Allstar was nearly zero. In three sunflower cultivars, with increasing of density and delaying of emergence time, flowering in redroot pigweed delayed and relative time of weed emergence was more effective than weed density. Earlier emergence of weed has higher effect on flowering delaying of Allstar, compared with two other cultivars. In all sunflower hybrids, time from flowering to seed maturity and growth period of redroot pigweed decreased in treatments with higher sunflower side branches.