Erysiphe necator is the causal fungus of grapevine powdery mildew disease and is one of the most widespread and consistently problematic pathogens of grapevine worldwide. Imported Vitis vinifera are among the most commonly grown grape species worldwide and are highly susceptible to powdery mildew infection. In the Northeastern United States where this study takes place, E. necator exclusively overwinters in its sexual stage as chasmothecia. Having a diverse genetic pool and mixed mode of reproduction contributes to a high evolutionary potential to overcome disease management methods; powdery mildews have been shown numerous times to overcome host resistance and several fungicide groups within a couple years of deployment. For this study, Amplicon Sequencing (AmpSeq) was performed on 3,170 field samples of E. necator collected between 2015 and 2020 with multiple timepoints per season investigated starting in 2018. This dissertation addresses the following questions: i) How accurately can disease severity predict the clonality or aclonality of single colonies? ii) Can a disease-date threshold be identified, by which if severity doesn’t exceed a given level by a certain late Summer date, pathogen winter survival can be prevented? iii) At what frequency are known fungicide resistance mutations identified in commercially managed vs. unmanaged native vine populations? iv) Are commercial populations less genetically diverse than unmanaged populations due to genetic selection in the form of frequent fungicide exposure?