The weeds create economic damage in crops with interfere in crops growth and abundance in agronomic systems. The One of most important items in create interference, is the phenomenon of allelopathy. In order to evaluate the effects of sunflower aqueous extracts, air and underground organs and the mixture of them on the germination and growth of Hoary cress weed seedlings, the experimental randomized complete block design with 13 treatments and 3 replications was conducted in Research Laboratory of the Faculty Agriculture, Birjand University in 2009. The test treatments consist of sunflower aqueous extracts, air and underground organs and mixture of them (equal to) four levels of 25, 50, 75 and 100 volumetric percentage plus control treatment (distilled water). The results of this experiment showed that the aqueous extracts in different organs of sunflower and the applied concentration had the significant effects on the germination and growth of Hoary cress weed seedling characteristics compared to control (p<0.01) was such that by increasing the concentration of aqueous extracts of sunflower various organs significantly decreased the germination percentage, length of radicle and coleoptile and seedling fresh weight. The application of the 100 volumetric percentage to the mixture extract of air and underground organs decreased to zero the seedling fresh weight and the length of the coleoptile. The estimation of three-parameter logistic model to lift used in this research showed that the air, underground and mixture organs of sunflower, in 97.34, 89.34 and 18.1 percentage of aqueous extract decreased the 50 percentage to maximum germination rate which in fact show more severe effects of the mixture organs of sunflower to compare the air and underground organs. based on orthogonal comparison in the aggregate assessed that the Sunflower mixed aqueous of air and underground organs extract had more preventative effects than the separate extracts on germination percentage, germination rate, length of radicle and coleoptile and seedling fresh weight of Hoary cress.
