Pectobacteriaceae are plant pathogens responsible for serious diseases on many crops of interest including potato. Currently, regarding the several disadvantages of conventional control by chemicals, the application of bio-agents as alternatives is increasingly being explored. The present investigation was conducted in order to evaluate the antibacterial activity of the fungal strain Trichoderma asperellum T34 as an antagonist against phytopathogen Dickeya solani on tubers of three potato varieties (Agata, Monalisa, and Picobello). For this, half-tubers were inoculated by T34 suspension with concentrations of 103 and 105 cells mL−1 at 6, 9, and 12 h before bacterial infection (D. solani at concentrations of 107 and 108 cfu mL−1). The results of infection assays without the antagonist indicated that Picobello variety was the least sensitive to soft rot, Monalisa and Agata varieties showed medium and high sensitivity, respectively. The antagonism assays revealed strong antibacterial activities, manifested by the regression of softened tissues gradually with the time of preincubation with T34, leading to a complete disappearance of disease symptoms using 12 h. Hence, the application of antagonistic Trichoderma strains as antimicrobial agents in the control of harmful plant pathogens is a subject of great interest and can be considered a promising strategy to handle soft rot diseases.