However, the growing interest in the substitution of "synthetic fungicides" by natural substances has fostered the research on aromatic plants and the screening of plant materials to identify new compounds. Essential oils (EOs) are complex mixtures constituted of terpenes compounds, which originate from the plant secondary metabolism.
Italian scientists have evaluated the efficacy of several EOs used alone and alternating with a synthetic fungicide in controlling powdery mildew. They tested an integrated control of powdery mildew on zucchini to reduce the use of synthetic fungicides and determined the main components of the EOs from Rosmarinus officinalis (R), Syzygium aromaticum (C) and Origanum vulgare (O) by GC-MS analysis. Moreover, they evaluated the residues of essential oils in zucchini leaves after treatments to determine the optimal interval between treatments.
Experimental trials were carried out in greenhouse during 2012–2013 testing different alternative application programmes.
Results showed that the alternation of essential oils and synthetic chemicals can control the disease, resulting that an integrated control management of zucchini powdery mildew is able to reduce the use of synthetic fungicides.
The main components detected in essential oils were 1,8-cineole (37%) in rosemary oil, eugenol (69%) in clove oil, thymol (40%) and carvacrol (18%) in oregano oil. As regards the residues of essential oil, results revealed that the a-pinene, 1,8-cineole, terpinen-4-ol, are not detectable after 7 days on leaves (the interval between one treatment and another), thymol and carvacrol persist up 1 h and until 3rd day, respectively, while the eugenol persists up 7 days in leaves. This can be explained by higher volatility of the first three compared to thymol, carvacrol and eugenol.
Scientists concluded that the weekly spray of essential oils and the alternated strategy with synthetic fungicide demonstrated the potential use of essential oils for management of powdery mildew on zucchini.
Source: Lucia Donnarumma, Filomena Milano, Stefano Trotta and Tiziana Annesi, ‘Use of Essential Oils in Control Strategies against Zucchini Powdery Mildew’, 2015, Journal of Phytopathology, doi: 10.1111/jph.12387.
For further info: http://onlinelibrary.wiley.com/doi/10.1111/jph.12387/abstract
Contacts:
Lucia Donnarumma
Centro di ricerca per la patologia vegetale, Consiglio per la Ricerca e la Sperimentazione in Agricoltura
Rome, Italy
Email: lucia.donnarumma@entecra.it