On the basis of laboratory experimental result (in vitro), three isolates namely T. harzianum (11), T. harzianum (16) and T. virens were selected for greenhouse studies. Biocontrol efficacy of these isolates and the combination of T. harzianum (11) and T. virens on rotten crown and root of sunflower were attempted in series of experiments using three methods; incorporation of spore suspension into the soil (107 spore/ g soil), incorporation of spore suspension with substrate into the soil (107 spore/ g compost) and impregnating of sunflower seeds with spore suspension (107 spore/ml). Experimental data were analyzed by Randomized Complete Block Design (RCBD) and means separated by Duncan's multiple range test. Glasshouse experiments (in vivo) showed that application of the combination of T. harzianum (11) and T. virens using incorporation of spore suspension with substrate into the soil (107 spore / g compost) all of the treatments was the most effective and prevented the crown and root rot of sunflower caused by S minor and S sclerotiorum by 50% and 41.66%, respectively. Consequently, the results indicated that the second method of antagonist application was the most effective in biocontrol of crown and root rot of sunflower caused by S. minor and S sclerotiorum.
