دوره بحراني كنترل علفهاي هرز دو رقم برنج نشايي در شرايط غرقابي

Critical period of weed control in two cultivars of paddy rice

To determine the critical period of weed control in rice, a split plot design was conducted with two factors including rice varieties (the improved cultivar of Khazar; and local cultivar of Binam) and hand weeding, in Rice Research Institute of Rasht in 2000. The experiment was conducted in a randomized complete block design with four replications and 10 treatments of hand weedings in two sets. The first set of treatments included weed free periods of 0, 10, 20, 30 and 40 days after rice transplantation (DAT), and the other set of treatments included weed infested periods of 0, 10, 20, 30 and 40 days. With 5 and 10% yield acceptable reduction, a critical period of weed competition between 10 to 51.3 and 20.5 to 44.2 DAT was obtained for Khazar, respectively. The critical period of weed competition in Binam was 23.4 to 39 and 29.7 to 32 DAT. The most dominant weeds of the field were Barnyardgrass (Echinochloa crus-galli), Bog-Bulrushes (Scripus mucronatus, S. juncoides), Umbrella-Nutsedge (Cyperus dofformis) and Water-Plantain (Alisma plantago). The costs of weed control in periods of weed competition was higher than the periods of weed control, so by delaying the control until 40 DAT, the time consuming for hand weeding exceeded three times to periods of weed control. The plant heights, number of filtering and leaves of weed control of both cultivars were lower than the weed free control, and increasing the DAT increased the range of differences. The paddy production of Khazar and Binam increased to 3.5 and 2.75 times of nontreated control, respectively, when the period of weed control reached to 30 DAT. The average of dry weeds in Khazar was more than Binam in all of the corresponding treatments.