determination of economic damage threshold of wild mustard in competition with four wheat cultivars at gorgan

for determination of economic damage threshold of four wheat (triticum aestivum l.) cultivars in different densities of wild mustard (sinapis arvensis l.), experiments were conducted at agricultural research station gorgan during 2010-2012. the experimental design consisted of four randomized complete blocks in a factorial arrangement. the treatments comprised of factorial combination of wild mustard densities and wheat cultivars. five different densities of wild mustard (zero, four, eight, 16 and 32 plants.m-2) and four wheat cultivars (‘arta’, ‘tajan’, ‘mogan’ and ‘morvarid’) were considered in all the replications. cousens hyperbolic equation was used to describe the yield reduction due to wild mustard competition. the maximum yield reduction was associated with high densities of wild mustard and among the cultivars, ‘arta’ and ‘morvarid’ had the maximum and minimum yield reductions, respectively. calculated competitive indexes indicated that ‘morvarid’ cultivar in competition with wild mustard had a high capacity to prevent yield loss (high tolerance) and on the other hand, dry weight and seed amount of weed was also greatly reduced. using extended cousens hyperbolic model and odonovan formula, economic damage threshold for wheat in two years determined in densities of 4.11, 3.68, 2.33 and 2.11 plant/m2 for ‘morvarid’, ‘moghan’, ‘tajan’ and ‘arta’ cultivars in climatic conditions of gorgan.