Field Evaluation of Thyme Oil 40 EC Formulation against Powdery Mildew (Erysiphe necator) of Grapevine (Vitis vinifera L.)

Grape (Vitis vinifera L.) is one of the most widely cultivated and economically important horticultural crops worldwide (Amores-Arrocha and Jiménez-Cantizano, 2025). Grapes are cultivated across temperate, subtropical and tropical regions and are utilized as table grapes and for the production of raisins, juice, wine and other value-added products (Alston and Sambucci, 2019; Khadatkar et al., 2025). Grapes also possess considerable nutritional and phytochemical value because they contain sugars, organic acids, vitamins, flavonoids, anthocyanins, tannins and bioactive polyphenols such as resveratrol (Fortes and Pais, 2016; Prathiksha and Hegde, 2022; Singh et al., 2023). In addition to their nutritional importance, grape production has substantial economic significance and represents one of the world's major high-value horticultural sectors (Alston and Sambucci, 2019; Amores-Arrocha and Jiménez-Cantizano, 2025).

Despite its economic importance, grape production is constrained by several fungal diseases and other biotic stresses (Malviya et al., 2022). Among these, powdery mildew caused by the obligate biotrophic fungus Erysiphe necator is one of the most widespread and economically important diseases of grapevine worldwide (Elfar et al., 2025). The pathogen can infect all green tissues of grapevine, including leaves, shoots, flowers and berries. Severe infections can result in flower and berry damage, reduced yield, berry splitting or cracking and deterioration of grape and wine quality. Most cultivated V. vinifera varieties are moderately to highly susceptible to E. necator, making effective disease management essential for maintaining grape yield and quality (Kunova et al., 2021).

Management of grape powdery mildew relies predominantly on preventive and repeated fungicide applications throughout the growing season. Under conditions favorable for epidemic development, 10–20 fungicide applications may be required, placing viticulture among the cropping systems with high fungicide-use intensity. Sulfur remains an important protectant fungicide, while several site-specific fungicides, including demethylation inhibitors and quinone outside inhibitors, have also been used effectively against E. necator (Reuveni, 2001; Kunova et al., 2021). However, intensive and repeated use of fungicides can increase the risk of resistance development in E. necator populations and can complicate long-term disease management (Kunova et al., 2021). The continued need for effective disease suppression therefore highlights the importance of integrating alternative or complementary disease-management approaches with conventional fungicide programmes.

Plant-derived essential oils have attracted increasing attention as potential tools for sustainable plant disease management because they contain diverse bioactive volatile compounds with antimicrobial properties. Essential oils commonly contain terpenes, terpenoids and phenolic compounds that may act against microorganisms through multiple mechanisms. For example, oregano essential oil contains carvacrol and thymol among its major constituents (Han et al., 2017). Importantly, the potential of essential oils against grape powdery mildew has also been demonstrated. Dhaliwal et al. (2002) reported antifungal activity of several essential oils against Uncinula necator, the former taxonomic name associated with E. necator, causing powdery mildew of grapevine. More recently, Reuveni et al. (2023) demonstrated that a hybrid formulation containing tea tree oil and difenoconazole provided high levels of field control of grape powdery mildew, indicating the potential of essential-oil-based formulations as components of integrated disease-management programmes.

Thyme oil is of particular interest because its major bioactive constituents, especially thymol and related phenolic compounds, are associated with antifungal activity. The antifungal action of thymol and carvacrol is generally attributed to disruption of fungal cell membranes, interference with ergosterol biosynthesis, inhibition of conidial germination, and disruption of mitochondrial function. However, compared with conventional fungicides and some other essential-oil-based products, field-based information on the efficacy of formulated thyme oil against grape powdery mildew remains limited. Therefore, evaluation of formulated thyme oil under vineyard conditions is warranted to determine its effectiveness in disease suppression, its potential contribution to yield protection and its phytotoxicity to grapevines.

Accordingly, the present investigation was undertaken to evaluate the bioefficacy of Thyme oil 40 EC formulation at different concentrations against powdery mildew of grapevine under field conditions during two successive seasons. The study further compared the efficacy of the thyme oil formulation with Hexaconazole 5% EC and Thiophanate-methyl 70% WP and assessed its effects on disease suppression, yield and phytotoxicity.