Chitosan-Based Bioactive Formulations for the Control of Powdery Mildew in Viticulture

Grapevine is highly susceptible to fungal diseases, whose incidence and severity increase due to climate change. The present work focuses on the assessment of eight combinations of natural products with chitosan oligomers with fungicidal capacity that may be effective in the integrated control of powdery mildew, in compliance with Article 14 of the European Directive 2009/128/EC. Their efficacy was evaluated in field conditions against natural infections, in a plot with high disease pressure during a growing season (assaying both foliar or root application), and against overwintering inoculums (chasmothecia) through in vitro tests. In addition, their possible biostimulant capacities were evaluated based on harvest yields. Treatments based on chitosan oligomers in combination with secondary metabolites of Streptomyces spp. and chitosan oligomers combined with hydrolyzed gluten showed the best results in terms of disease control. Given the high efficacy of these formulations, comparable to that of conventional antifungals, they constitute an interesting alternative for the control of this disease whose treatment can, in some cases, represent almost half of the production costs.