Vineyard evaluation of stilbenoid‐rich grape cane extracts against downy mildew: a large‐scale study

BACKGROUND Plasmopara viticola control in organic viticulture requires copper‐based fungicides with harmful effects on health and the environment. Plant extracts represent a biorational eco‐friendly alternative to copper. The aim of this study was to evaluate the potential of stilbenoid‐rich grape cane extract (GCE) against downy mildew on three cultivars over 3 years following natural downy mildew infection. RESULTS Over all field trials, GCE treatments showed an average reduction in disease incidence of −35% and −38% on leaves and clusters, respectively. The average reduction in disease severity was −35% and −43% on leaves and clusters, respectively. Under artificial downy mildew infection, GCE efficacy corresponded to 1 g L −1 of copper. Neither phytotoxicity nor adverse effects on auxiliary fauna were observed after treatment with GCE. CONCLUSION Because few or no biocontrol agents are active alone against P. viticola , GCE is a promising alternative to copper‐based fungicides. Grape canes, an abundant by‐product of viticulture, have great potential for valorization as a biocontrol agent for sustainable viticulture.