Grapevine trunk diseases (GTD) and young vine decline (YVD) present major challenges for vineyard health and productivity worldwide. Recent investigations in California highlight how nursery propagation practices and microbial communities associated with planting material strongly influence the development and severity of these diseases. Metabarcoding and culture-based surveys of nursery plant material revealed a complex assemblage of GTD-associated fungi, including well-known pathogens causing Petri disease, black foot, Botryosphaeria dieback, Phomopsis dieback, and Eutypa dieback. Infections often begin in mother vines and intensify as cuttings progress through propagation pipelines, particularly increasing the incidence of Petri disease-associated fungi and Fusarium species. Although Fusarium has not traditionally been considered a primary GTD pathogen, extensive pathogenicity trials identified multiple Fusarium species—especially Fusarium annulatum—causing necrotic lesions in young vines, thereby implicating these fungi as contributors to YVD. In addition to pathogens, the broader grapevine microbiome, including both fungal and bacterial communities, significantly affects vine health and yield. A comprehensive field study demonstrated that specific microbial taxa from trunk, root, and rhizosphere samples correlate strongly with yield, explaining a majority of yield variance in a three-year-old vineyard. Beneficial microbes, as well as novel, poorly characterized taxa, emerged as potentially valuable bioinoculants for improving vine performance. Collectively, these findings underscore the critical importance of managing the grapevine microbiome—both harmful and beneficial organisms—through improved nursery protocols, planting material screening, and the strategic use of microbial inoculants to mitigate GTD, reduce YVD incidence, and enhance vineyard productivity