- Grapevine Trunk Diseases (GTDs) are caused by a group of fungal pathogens that attack the xylem tissue of mature grapevines worldwide. In the past 30 years, their incidence has increased, both in emerging grape-producing regions, as well as those with an extended history of viticulture. In the same time span, our understanding of GTDs as a whole has shifted. Once considered a small handful of independent diseases, diseases such as Eutypa dieback, Esca, and Botryosphaeria dieback are now grouped together due to shared symptoms. However, the ever-growing list of GTD-associated species suggests complexity in this system that relates to fungal communities more broadly than was once considered. To explore how fungal communities vary along gradients of GTD disease incidence, vineyard age, and geography in Oregon we conducted a molecular field study, amplifying the ITS1 region of fungal rDNA extracted from vine stem tissue sampled from 29 vineyards in the Rogue and Willamette Valleys (n= 396). More specifically, our goals are to (1) identify which GTD species are most prevalent in the fungal microbiome, (2) examine differences in GTD species between the two valleys, and (3) compare our results generated with ITS metabarcoding with published, culture-based results generated from the same samples. In total, we found over 2000 Operational Taxonomic Units (OTUs) in stem tissues, predominantly in the Ascomycota (85%) and Basidiomycota (14%). The most abundant genera, Cladosporium (30%), Penicillium (8%), Seimatosporium (7%), Alternaria (5%), and Aureobasidium (5%), were not associated with core GTD genera, regardless of disease incidence. However, significant correlations between the most abundant OTUs and GTD associated genera suggest interactions between core GTDs.