In anticipation of the food crisis, developing innovative products and technologies to increase crop yield and quality is a necessity. In this context, the aim of this study was to develop a phytostimulant based on Tagetes erecta extract and rhizobacteria to increase the antifungal activity against phytopathogenic fungi. The hydroalcoholic extract from T. erecta flowers was characterized by UV-Vis spectrophotometric assays (total phenolic content, total flavonoids content, reducing sugar content), qualitatively by ATR-FTIR and quantitatively for individual compounds by UHPLC-HESI analysis. The antioxidant activity was evaluated and the phytostimulation capacity was done on the radish and cucumber. The variants of the concentration that stimulated the rhizobacteria (Bacillus sp.) proliferation were selected by evaluating the influence on the microbial viability in a liquid medium. The antifungal activity against fungal pathogens (Monilinia laxa, Fusarium graminearum, Aspergillus niger) was determined by reducing mycelium growth in solid and liquid media. The synergistic effect between optimal levels of rhizobacteria-containing T. erecta extract showed a significant decrease in mycelium development. Thus, PGPR strains treated with T. erecta extract could be applied as biocontrol agents against plant pathogens and stimulate vegetable seedlings.