Interference of redroot pigweed (Amaranthus retroflexus L.) in green bean (Phaseolus vulgaris L.)

Several species of Amaranthus are known to reduce crop yields and interference with harvest throughout the Iran. In the past few years, the occurrence of some Amaranthus species including of redroot pigweed (Amaranthus retroflexus L.) increased throughout the East Azerbaijan province in Iran, supplanting all the other Amaranthus species in large areas of the region and causing concern among farmers and researchers. Green bean (Phaseolus vulgaris L.) is one of the tropical pulse crops, that C4 weeds such as redroot pigweed can cause yield loss in this crop production. In order to determine the critical period of redroot pigweed control in green bean, two experiments were conducted in Islamic Azad University of Tabriz, Iran, at 2004 and 2005. The experimental designs in both year was a randomized complete blocks with three replications. The treatments were weed-infested and weed-free in the same periods. Both year, in weed-infested experiment, redroot pigweed was seeded immediately after green bean planting and removed after 0, 2, 4, 6, 8, 10 and 14 weeks after green bean emergence (WAE). In weed-free experiment, redroot pigweed seeds were transplanted to green bean plots at 0, 2, 4, 6, 8, 10 and 14 WAE. Data were analyzed using the MSTATC software and means were compared using Duncan's Multiple Ranges Test. Regression analysis was performed to describe the relationship between green bean yield and duration of redroot pigweed interference using the REG PROCEDURE of SAS. Results indicated that the difference between years with a view to influence on all traits except stem height at the harvesting stage and pod yield at the first and second harvesting time were significant. Also, differences between treatments with a view to influence on all traits were significant. Contemporary growing of pigweed and green bean for early first month and weed interference 10 WAE had not significant effect on green bean above ground biomass. In both years, the highest green bean yield loss measured in full-season weed interference. Based on fitted equations for weed-infested (sigmoid model) and weed-free (cubic model) plots, were critical periods of weed control with 5 and 10% yield loss in 13 to 60 and 19 to 55 days after green bean emergence. Obviously, farmers with using of such experiment results could control weeds in the best time and with decreasing of herbicide use, we can move toward some purposes of the sustainable agriculture.