Rye (Secale cereale L.) is one of the important weeds in winter wheat fields of Iran. The competition effect of rye on growth indices of winter wheat (Triticum aestivum) was evaluated at the Plant Pests and Diseases Research Institute and College of Agriculture, Tehran University, Karaj (Iran) during 2001-2002. The experimental design was randomized complete block with 24 treatments and 4 replications. The was bivariate factorial. The treatments included the pure stands of wheat at four densities of crops 350, 450, 550 and 650 plant/m2 and pure stand of rye at 10, 30, 50 and 70 plant/m2, and mixed densities of two plants in all possible combination of densities montaned. Samples were collected from 0.12 m2 from plots in 15 days interval. Growth characteristics such as leaf area and dry matter were recorded and used to calculate growth indices including leaf area index (LAI), dry matter accumulation (DMA), and crop growth rate (CGR). Results indicated that density of 650 plant/m2 of wheat had maximum LAI and that of 350 plant/m2 of wheat had minimum LAI. The density of 550 plant/m2 of wheat had maximum DMA. At low densities of rye (up to 10 p/m2) the density of 550 plant/m2 of wheat had maximum CGR and at high densities of rye CGR of 450 and 550 plant/m2 of wheat were not different. The density of 350 plant/m2 of wheat had minimum CGR.
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