Increasing demands to reduce harmful environmental effects from the overuse of various herbicides has encouraged the development of weed management systems, which are dependent on ecological approaches rather than agrochemicals. Four studies have been carried out to biocontrol and manage of tow weeds, field bindweed ( Convolvulus arvensis L . ) and red-root pigweed ( Amaranthus retroflexus L.) by pathogenic fungi and allelopathy. First study was done to find the most effective fungi against C. arvensis and A. retroflexus. One fungus, Alternaria sp., was isolated from A. retroflexus which had very low mortality in it. But fungi were isolated from C. arvensis including Alternaria sp., Cladosporium sp., Fusarium compactum , Chaetomium globosum , Phaeoacremonium sp . had high mortality in field bindweed. The highest levels of plant mortality were obtained from treatment of Alternaria sp. (Isolate AI 3 ). These fungi have not pathogenic effects in evaluated crops including Glycine max, Lycopersicon lycopersicum, Carthamus tinctorius, Solanum tuberosum , Beta vulgaris , Triticum aestivum , Hordeum vulgare, Zea mays . This experiment confirms the potentiality of Alternaria sp. as a mycoherbicide for C. arvensis . Second study has been carried out to bioassay phytotoxic effects of 6 plant extracts including Crocus sativus , Ricinus communis , Nicotiana tabacum , Datura inoxia , Nerium oleander and Sorghum vulgare on germination, seedling growth and seedling antioxidant enzyme activities (Catalase (CAT), Guaicol peroxidase (GPX) and Ascorbate peroxidase (APX)) of field bindweed. Aqueous extracts were used at four concentrations including 2.5, 5.0, 7.5 and 10 gL -1 . Extracts of R.communis , N.tabacum , D.inoxia and S. vulgar showed the most inhibitive effect on germination and seedling growth of field bindweed, while the rest extracts ( C. sativus and N. oleander ) had the least effect. C.sativus , N.tabacum and N. oleander extracts increased CAT activity but other extracts reduced its activity in seedlings. Furthermore, all extracts increased GPX and APX activities which might be the reaction of field bindweed to reduce toxic effect of phytotoxins. The results of this experiment showed that extracts of R.communis , N. tabacum , D. inoxia and S. vulgar could be used as pre emergence herbicide. Third study was conducted to examine the allelopathic potential of C. sativus, R. communis , N. tabacum , D. inoxia , N. oleander and S. vulgar on growth of C. arvensis in pot experiment. The effects of 10 gL -1 aqueous extract and 0, 1, 2 and 4 t ha -1 powders of all the tested species were used in two separated pot experiments to determined their allelophatic potentials on plant height, dry weight, number of survivor plant, leaf area, chlorophylls (a, b and total) and carotenoid contents of field bindweed. Results showed that aqueous extracts of R. cummunis , N. tabacum , D. inoxia and S. vulgar significantly (p 0.05) inhibited germination and seedlings growth of field bindweed and the effects were concentration specific; as the concentration of extracts increased the allelopathic effects were more pronounced. Application of 10 g L -1 aqueous extracts of all tested species significantly (p 0.05) reduced all of measured traits, but their effects depended on the species type. Besides, all of the powder treatments influenced the measured parameters including dry weight, height, leaf area as well as chlorophyll and carotenoid contents. The results demonstrated that both aqueous extracts and powders of tested species could be used as post emergence bioherbicides against C. arvensis . In greenhouse experiment extracts (only 10 gL -1 concentration was used) and powders of these plants also showed significant inhibitory effect on red-root pigweed dry weight, height, leaf area, number of survivor plant and amount of chlorophyll. In application of powders the inhibitory effect was dosage dependent and the higher concentration had the strongest inhibitory effect. According to the results, it can be concluded that powders and extracts of the tested species have the herbicidal potential against red-root pigweed and could be used as natural herbicides and mulches.