evaluation of competition of early watergrass (echinochloa oryzicola (ard) fisher) on rice fields of guilan

ٍearly watergrass (echinochloa oryzicola (ard) fisher) is an aggressive specie of echinochloa and have mimicry chareterstics of rice . in order to evaluate competitive effect of aggressive specie of echinochloa on rice, an experiment was conducted at the rice research institute of rasht during 2007. the experimental design was complete randomized block with three replications. the treatment included weeds density at three densities (10, 20 and 40 plant/m2) and rice was transplanted with local normal density (20 bunch.m-2 and each bunch included three plants). result indicated that early water grass decreased grain yield, the number of panicle per plant, biologic yield and harvest index were significantly at possible area 1%. when density increased until 40 plant.m-2, grain yield lossed was 70%. loss of number seed per panicle in densities 10, 20 and 40 plant/m2 was 34, 41 and 43 present and loss of number panicle per plant of rice in competition to echinochloa was 62, 64 and 62 present respectively. densities of 10, 20 and 40 plant.m-2 decreased average of rice height to 49, 67 and 61 present, respectively. rice in densities 40 plant.m-2 of weed had less highest and in densities 0 plant.m-2 the highest.