The studies showed significant inhibitory effects of potassium bicarbonate (KHCO₃) either on growth parameters of Sclerotium rolfsii or in sunflower root/collar.  Inhibitory effects were increased by enhancing KHCO₃ concentration. KHCO₃ gave significant inhibitory effects against Sclerotium rolfsii caused76.6, 57.69 and 95.78% inhibition for linear growth, sclerotial formation and mycelial dry weight, respectively at 0.6g/l KHCO₃.KHCO₃provided synergistic effects with Trichoderma harzianum, Since the antagonistic potentiality of T.harzianum against S. rolfsii was increased with increasing KHCO₃ concentrations. KHCO₃  caused 80 and 76% inhibition for linear growth and sclerotial formation, respectively. However, the most effective to prevent growth parameters and infectivity of  S.rolfsii  the combinations of potassium bicarbonate and hydrogen peroxide (H₂O₂) with Trihoderma harzianum 86.25% and 97.6% inhibition for radial growth and sclerotial formation at H₂O₂ (1.2 g/l) +KHCO₃ (0.6 g/l) with T.harzianum , respectively. The treatments H₂O₂ (1.2 g/l) +KHCO₃ (0.3g/l) with T.harzianum and H₂O₂ (1.2 g/l) +KHCO₃ (0.6 g/l)  with T.harzianum  achieved  75% and 71% protection against sunflower basal stem rot, respectively.