Applications of Ozonated Water for Effectively Controlling Grape Powdery Mildew in Vineyards and Enhancing Berry Metabolites

Powdery mildew of grapevines (Vitis vinifera), caused by Erysiphe necator, poses a significant threat to grape production globally. While synthetic fungicides have traditionally been the primary means of combating this disease, the imperative to reduce pesticide use and to curb the development of fungicide resistance necessitates the exploration of alternative management strategies. We assessed the effectiveness of ozonated water against grape powdery mildew in field trials and large-scale demonstrations in Israel. Preventive foliar applications of ozonated water at 7- or 14-day intervals from 15 to 25 cm shoot length until véraison effectively controlled powdery mildew on wine grape clusters, providing 85%–100% efficacy in reducing disease incidence and severity compared with untreated vines. Furthermore, whole canopy application of ozonated water, sprayed directly on leaves and clusters in the vineyard, enhanced the accumulation of polyphenolic metabolites in berry skins, including stilbenes and flavonoids such as piceid, α-viniferin, isoquercetin, resveratrol and anadanthoside, compared with grapevines treated with fungicide. These compounds have the potential to improve wine quality and enhance plant tissue resistance against pathogens. Piceid, α-viniferin and isoquercetin significantly inhibited in vitro spore germination of E. necator with 97%, 90% and 52% inhibition observed at 100, 10 and 1000 ppm, respectively, relative to controls. The high efficacy, promotion of antifungal metabolites in berries, low cost, low toxicity and environmental safety of ozonated water position it as an ideal preventative treatment for disease control in vineyards. Moreover, its use could reduce fungicide usage and may mitigate the development of fungicide resistance during the growing season.