Reducing copper use in the environment: The use of larixol and larixyl acetate to treat downy mildew caused by Plasmopara viticola in viticulture

SummaryBACKGROUND Plant extracts might provide sustainable alternatives to copper fungicides, which are still widely used despite their unfavourable ecotoxicological profile. Larch bark extract and its constituents, larixyl acetate and larixol, have been shown to be effective against grapevine downy mildew (Plasmopara viticola) under semi-controlled conditions. The aim of this study was to reduce the gap between innovation and the registration of a marketable product, namely to develop scalable extraction processes and to evaluate and optimize performance of larch extracts under different conditions. RESULTS Toxicologically and technically acceptable solvents like ethanol were used to extract the active compounds larixyl acetate and larixol from bark in sufficient amounts and their combined concentration could be increased up to 39% by purification steps. The combined concentration of larixyl acetate and larixol from larch turpentine could be increased up to 66%. MIC100 against P. viticola in vitro (6-23 μg mL-1) and EC50 in planta under semi-controlled conditions (0.2-0.4 mg mL-1) were promising compared to other plant extracts. In vineyards, efficacies of larch extracts reached up to 68% in a stand-alone strategy and 84% in low-copper strategies. CONCLUSIONS Larch extracts represent valid candidates for copper reduction in organic vineyards, and their development into a sustainable plant protection product might be feasible.