ABSTRACT.- The antifungal activity of Chenopodium ambrosioides essential oil against Penicillium digitatum was evaluated in vitro (liquid phase) and in vivo on artificially inoculated Okitsu Satsuma mandarin (Citrus unshiu). In vitro, the essential oil exhibited a fungicidal effect, with 100% effectiveness at a minimum inhibitory concentration of 29 uL/mL, and a minimum fungicidal concentration of 125 uL/mL. However, in vivo, P. digitatum grew on over 80% of treated fruit, showing no significant
difference from the control. With the purpose of contributing to the knowledge of the causes that explain the loss Ch. ambrosioides essential oil effectiveness in vivo, the effect of some aspects related to citrus fruit peel in the interference between the essential oil and the pathogen were explored. The results demonstrated that, despite its strong in vitro fungicidal activity, the efficacy of Ch. ambrosioides essential oil in controlling P. digitatum on citrus fruits may be compromised by interactions with rind components. © 2025 Informa UK Limited, trading as Taylor & Francis Group.