How does leaf age affect performance? A comparative study of essential oils from young and mature Eucalyptus globulus leaves in crop protection

BACKGROUND Essential oils (EOs) from Eucalyptus globulus Labill. leaves are widely recognized for their biological properties. However, the influence of leaf age on EOs chemical composition and bioactivity remains unclear. This study aimed to characterize the chemical profiles and biopesticidal potential of EOs extracted from juvenile leaves from young trees (YEEO) and adult leaves from mature trees (AEEO) against relevant agricultural pests and pathogens. RESULTS Metabolomic profiling revealed similar overall compound diversity between YEEO and AEEO. YEEO contained higher levels of α‐pinene and β‐pinene, whereas AEEO was richer in oxygenated compounds, such as 1,8‐cineole and trans‐pinocarveol. Herbicidal activity was tested against Portulaca oleracea and Solanum nigrum in pre‐ and post‐emergent assays, showing strong post‐emergent effects with 100% mortality at the highest concentrations. Both EOs also displayed dose‐dependent antibacterial activity, with Clavibacter michiganensis subsp. michiganensis being the most susceptible, followed by Xanthomonas euvesicatoria and Pseudomonas syringae pv. tomato . No antifungal activity was observed against Alternaria alternata or Botrytis cinerea , but both EOs exhibited potent insecticidal activity against Phthorimaea absoluta larvae, achieving total mortality at the highest concentration (50% v/v) and low LC₅₀ (15.2% v/v for YEEO and 14% v/v for AEEO) and LC₉₀ values (41.4% v/v for YEEO and 38.5% v/v for AEEO). CONCLUSION Despite their chemical differences, YEEO and AEEO showed comparable herbicidal, antibacterial, and insecticidal effects, highlighting the feasibility of large‐scale EO production, especially by valorizing adult leaves, a by‐product of the paper and furniture industries. These findings highlight the potential of E. globulus EOs as bioactive agents against weeds, insects, and bacteria; however, further field studies are required to evaluate their practical applicability.