Choline pelargonate treatments decreased downy mildew and powdery mildew symptoms with negligible effects on grapevine phyllosphere micro-organisms

: Grapevine is an important crop worldwide, but most cultivars are susceptible to downy mildew and powdery mildew. This study aimed to evaluate the efficacy of choline pelargonate (CP) against grapevine downy mildew and powdery mildew under controlled and field conditions, and to assess its effects on phyllosphere micro-organisms. CP decreased the severity of both pathogens under greenhouse and field conditions. In greenhouse trials, 16 mM CP showed efficacy comparable to copper and sulfur applied at label-recommended concentrations as reference fungicides in organic viticulture. CP showed direct inhibitory activity against both pathogens, and slightly induced defense-related grapevine genes (CHIT-3, OSM-2, and PR-1). Field experiments corroborated the efficacy of CP against powdery mildew and downy mildew severity on leaves and bunches. Microbial community analysis revealed that plant compartment, vineyard location, and sampling time were key drivers of microbial community structure, while treatments showed negligible effects on microbial alpha-diversity and beta-diversity of grapevine leaves and bunches. CP treatment partially modified the relative abundances of some bacterial and fungal taxa, while reference fungicides caused broad changes across multiple genera. CP showed promising antifungal activity with minimal effects on phyllosphere micro-organisms, supporting its potential as a sustainable disease management approach that preserves indigenous microbial communities.