In order to determine the effects of density of red root pigweed on growth and physiological parameters of corn, an experiment was conducted in Faculty of Agriculture, Islamic Azad University of Fasa, located in southeastern region of Fars Province in Iran. The experiment involved the effects of various densities of red root pigweed at five levels including zero, 1, 2, 4, and 8 plants in each meter of plant row on the yield and yield components of single cross 500 corn variety, carried out in

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... e form of complete randomized blocks design in three replications under farm conditions. The results showed that the highest yield of corn was obtained under no pigweed treatment, which had no significant difference with the treatment involving the density of one pigweed plant in each meter of planting row. The lowest yield for corn was obtained when the density of pigweed was 8 plants, which had no significant statistical difference with the treatment involving 4 plants of pigweed in each meter of planting row. Among the yield components, the highest weight of 1000 grains, the number of grains in each cob, and the number of grains in each row of corn cob were obtained under the treatment involving no pigweed and the lowest values for these components were obtained under the treatment involving eight plants of pigweed in each meter of planting row, with no significant difference with the 4 plant treatment.