Induced resistance (IR) based on elicitors application aims to strengthen plant defenses, rather than directly targeting pathogens. These compounds are less toxic than conventional pesticides and are useful in reducing their use. Strategies based on COS–OGA, Swinglea glutinosa, and low copper doses were tested in this three-year (2021–2023) field investigation against grapevine downy (DM) and powdery (PM) mildew. Their effectiveness was compared to copper, sulfur, untreated, and water-sprayed plants in a naturally infected vineyard. Combined treatments provided higher levels of protection. COS–OGA at 2 L ha⁻¹ combined with low copper doses and an adjuvant protected canopy and production from both DM and PM at the same level as copper and farm application (based on copper and sulfur). In favorable seasons, 2023 for DM and 2022 for PM, this strategy reduced the DM McKinney Index compared to untreated plants by 74% and 39% on leaves and bunches, respectively. Reductions observed for PM were 85% on leaves and 46% on bunches. S. glutinosa showed reductions only in one assessment against PM on bunches. This work validates IR-based DM and PM management strategies under field conditions and paves the way toward concrete reduction in copper and sulfur use in vineyards.

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.