Botrytis cinerea infections of Vitis spp. fruits cause major economic losses, and grape producers rely on synthetic and copper-based fungicides for control of this pathogen. These pesticides present risks for human health and the environment. Implementation of low-impact disease management solutions is important for improving sustainability of viticulture industries. This study investigated the effects of Origanum vulgare (oregano) essential oil (EO) as an antifungal agent. In vitro and in vivo experiments with B. cinerea were carried out using a vaporization system to circumvent drawbacks of direct EO application. In vitro experiments confirmed the effectiveness of EO vapour treatments, which gave 100% inhibition of B. cinerea growth. Treatment of V. vinifera cv. Chasselas berries resulted in a 73% reduction in fungal growth, confirming the efficacy of the oregano EO vapour for control of grey mould caused by B. cinerea. This study has demonstrated the efficacy of EOs in the vapour phase on grape berries, which provides new possibilities for development of in-field or greenhouse vaporization systems that can reduce the use of synthetic and copper-based fungicides.