Use of Basic Substances and Other Natural Compounds as Alternatives to Synthetic Fungicides for the Control of Grapevine Downy and Powdery Mildews

Consumer demand, retailer involvement, policies to reduce pesticide application, and the growth of organic agriculture are steering research toward safer alternatives like basic substances: compounds used as food, food ingredients, or in medicine with a potential secondary application in plant protection. Downy mildew (DM) and powdery mildew (PM) are major grapevine diseases, and many fungicide applications are required for their management. In this 2-year field trial, chitosan, whey, sweet orange essential oil (EO), Equisetum arvense, Urtica spp., and Ampelomyces quisqualis were tested against DM and PM in repeated stand-alone treatments (10 applications in 2022 and 11 in 2023) on cultivar Montepulciano in Italy. Their effectiveness was compared with copper and sulfur. Untreated plants and water-sprayed plants served as two negative controls. The disease McKinney Index was calculated based on incidence and severity, following visual assessments. Several compounds reduced the amount of DM and PM. Chitosan 0.5% and sweet orange EO 600 ml/hl provided the highest protection levels, reducing the DM McKinney Index on leaves up to 94 and 91% compared with the untreated control. Against PM, both treatments achieved a 98% reduction. Reductions on bunches were up to 72 and 47% for DM and 40 and 37% for PM. For two consecutive years and under high disease pressure, chitosan proved as effective as copper in managing DM on both leaves and bunches. This trial explored some natural compounds as additional tools for DM and PM management. Further studies are crucial to validate their effectiveness across different environments, disease levels, and cultivars.