Low‐dose antifungal activity of plant extracts against crop pathogens: Evidence for E quisetum arvense

Background Plant extracts have emerged as eco‐friendly alternatives to synthetic pesticides, acting as bioinsecticides, biobactericides, or biofungicides. Results This study evaluated the antifungal activity of nine plant extracts: Croton lechleri , Flourensia cernua , Viscum album , Equisetum arvense , Allium sativum , and Eucalyptus globulus (ethanolic extracts), as well as aqueous extracts of Flourensia cernua , Equisetum arvense , and Fouquieria splendens , all applied at a low concentration (1:300 v/v in PDA). Radial growth inhibition was tested for four phytopathogenic fungi: Botrytis cinerea , Penicillium expansum , Fusarium sp., and Pestalotiopsis sp. The aqueous extract of Equisetum arvense displayed the strongest inhibition, being active against all four strains, with up to 85.8% inhibition against Fusarium sp. HPLC‐MS analysis revealed a diverse array of bioactive compounds, including flavonols and hydroxycinnamic acids, many of which have been reported to exhibit antifungal activity. After 6 months of storage, the extract lost its inhibitory activity, which correlated with the degradation of key metabolites. This is, to our knowledge, the first report of a low‐dose aqueous extract of E. arvens e with strong broad‐spectrum antifungal activity. Conclusions These findings support its potential as a basis for developing biopesticides for postharvest protection and highlight the importance of stability studies and formulation strategies for commercial application.