Hemp (Cannabis sativa L.) is an emerging crop in the United States with a market that is currently developing strong potential to grow. Several pathogens of hemp have emerged in recent years including powdery mildew, caused by Golovinomyces ambrosiae. Powdery mildews are a large group of obligate biotrophic plant pathogens that have major impacts on many crops worldwide. The highly polycyclic nature of powdery mildews can make disease management challenging, as disease pressure increases rapidly after initial infection. Therefore, the identification of effective management strategies is crucial for hemp production. The first goal of this research was to begin to determine the host range of G. ambrosiae. Most powdery mildews have a relatively narrow host range, but prior to this research, G. ambrosiae had been reported on several other crops. This work demonstrated that okra (Abelmoschus esculentus), sunnhemp (Crotalaria juncea), sunflower (Helianthus annuuss), some cucurbits (Cucurbita pepo) and some Zinnia (Zinnia elegans) are hosts of G. ambrosiae with varying levels of susceptibility. Through this work I was also able to identify several fungicides that were effective in controlling powdery mildew in the field. However, those same products were not effective against the necrotrophic pathogen, Botrytis cinerea, the causal agent of gray mold on hemp. I was also able to determine that infection with G. ambrosiae or fungicide application largely did not impact cannabinoid production in hemp, while B. cinerea potentially had an impact. Lastly, this work sought to identify possible sources of genetic host resistance to G. ambrosiae. I was able to observe a wide range of disease susceptibility among the hemp germ plasma, including high cannabidiol (CBD), high cannabigerol (CBG), fiber, grain and dual-purpose hemp cultivars and accessions, throughout multiple field seasons and growth chamber inoculations. From these disease ratings, one resistant cultivar was identified and crossed with a susceptible cultivar to create a mapping population with the goal of identifying the responsible gene(s). The resulting F1 and F2 populations have been characterized for disease susceptibility. All this information contributes to the knowledge about G. ambrosiae, with the goal of improved disease management strategies and tools.