The study, conducted with the aim of protecting market garden crops, focused on the medicinal plant Inula viscosa, whose essential oil was evaluated for its fungicidal efficacy against phytopathogenic fungi affecting Solanum melongena L. (eggplant). The essential oil yield was relatively high, approximately 1.53%. The major constituents of Inula viscosa essential oil were germacrene D (12.7%), δ-cadinene (9.6%), and α-cadinol (8.5%). The essential oil demonstrated notable effectiveness, with mycelial growth inhibition rates for the tested fungal strains—Epicoccum sp., Geotricum sp., Aspergillus niger, and Trichoderma sp.—ranging from 2.35% to 100%, depending on the concentration used. A comparative study of the inhibitory efficacy of Inula viscosa essential oil and the fungicide Vapcotop revealed the superior activity of the essential oil against Epicoccum sp., Geotricum sp., and Aspergillus niger. However, Trichoderma sp. was more sensitive to Vapcotop than to the essential oil. These promising results support the recommendation of Inula viscosa essential oil as a natural alternative to synthetic fungicides, contributing to the protection of Solanaceae crops while preserving both environmental and human health.