Abstract Cercospora beticola, the causative agent of cercospora leaf spot (CLS) disease, is a serious problem that remarkably impact the yield of sugar beet worldwide. Our aim was to assess the antifungal effect of a natural and more safe extracts of Leaves, flowers and stem bark of Cassia nodosa and salicylic acid (SA) individually or in combination relative to the recommended treatment tetraconazole fungicide. The fungicidal effect was assessed in vitro by measuring the radial growth of C. beticola and in vivo by determining the alteration in CLS disease severity, sugar beet root weight and quality traits (sucrose, total soluble solids and purity %). Also, the relationship between disease severity % and root weight, sucrose % and leaf biochemical components was determined. In vitro, all the tested plant extracts at different concentration levels inhibited the growth of C. beticola. The results of all in vitro and in vivo experiments were revealed that the best effects were for n-butanol extract of stem bark, methanolic extract of flowers and ethyl acetate extract of stem bark either alone or in combination with SA. Stem bark n-butanol extract was the most effective one. Four salicylic acid-plant extract mixtures demonstrated a synergistic effect (SA with flowers methanolic, leaves ethyl acetate, and stem bark ethyl acetate and n-butanol extracts). A highly significant negative correlation was found between CLS severity % and all of root weight, sucrose % and biochemical components of sugar beet leaves.