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Microbial agents such as the <i>Bacillus</i> species are recognized for their role as biocontrol agents against various phytopathogens through the production of diverse bioactive compounds. This study evaluates the effectiveness of <i>Bacillus subtilis</i> PE7 in inhibiting the growth of <i>Didymella bryoniae</i>, the pathogen responsible for gummy stem blight (GSB) in cucurbits. Dual culture assays demonstrate significant antifungal activity of strain PE7 against <i>D. bryoniae</i>. Volatile organic compounds (VOCs) produced by strain PE7 effectively impede mycelial formation in <i>D. bryoniae</i>, resulting in a high inhibition rate. Light microscopy revealed that <i>D. bryoniae</i> hyphae exposed to VOCs exhibited abnormal morphology, including swelling and excessive branching. Supplementing a potato dextrose agar (PDA) medium with a 30% <i>B. subtilis</i> PE7 culture filtrate significantly decreased mycelial growth. Moreover, combining a 30% culture filtrate with half the recommended concentration of a chemical fungicide yielded a more potent antifungal effect than using the full fungicide concentration alone, inducing dense mycelial formation and irregular hyphal morphology in <i>D. bryoniae</i>. Strain PE7 was highly resilient and was able to survive in fungicide solutions. Additionally, <i>B. subtilis</i> PE7 enhanced the nutrient content, growth, and development of melon plants while mitigating the severity of GSB compared to fungicide and fertilizer treatments. These findings highlight <i>B. subtilis</i> PE7 as a promising biocontrol candidate for integrated disease management in crop production.