Combating Two Major Fungal Diseases in Marigold (Tagetes spp.): Insights into Pathogen Identification and Antifungal Strategies

Marigold (Tagetes spp.), a widely cultivated popular ornamental plant that is highly susceptible to fungal diseases, particularly leaf spot and stem wilt, which can substantially reduce its ornamental and economic value. This study aimed to identify the causal pathogens responsible for these diseases and evaluate the efficacy of selected antifungal agents against them. The causal agent of leaf spot was identified as Alternaria alternata, whereas stem wilt was caused by the Fusarium solani species complex (FSSC), based on Koch’s postulates, morphological characterization, and molecular identification. The antifungal activities of five commercially available fungicides were subsequently evaluated against both pathogens. The results showed that isomycete fluridine suspension (40%), metalaxyl–oxametrin suspension (32%), eugenol liquid (0.3%), pyrazolesterin methyl thiobacillin suspension (41%), and pyrazolesterin tebuconazole suspension (30%) demonstrated varying degrees of inhibitory activity. The EC50 values for A. alternata ranged from 10.588 to 49.604 mg/L, while those against FSSC ranged from 12.273 to 27.921 mg/L. These findings provide insights into the potency of these fungicides and offer a scientific basis for developing integrated disease management strategies for marigold cultivation, although further research is required to validate and evaluate their long-term efficacy and environmental safety.