Technical Abstract: The effects of various cover crops (sordan, mustard, canola, honeysweet, and fallow) to influence soil fungal biomass and diversity were tested in a potato field in the San Luis Valley, Colorado. Soil samples (0-5 cm depth) were randomly selected from each cover crop plot and soil fungal communities were analyzed based on fungal DNA profiles. All cover crops increased the soil fungal biomass as compared to the fallow treatment, with the greatest fungal biomass in the sordan plots. On average, 13 different fungal species were identified in each of the various cover crops. Of these species, three are known potato pathogens (Fusarium equiseti, Verticillium sp., and Alternaria solani). Cover crops differed in their ability to suppress, or reduce biomass, of these pathogenic species. For example, the mustard cover crop significantly reduced the biomass of all three species; whereas, sordan significantly reduced both Verticillium sp. and Alternaria solani. Sordan appears to be a beneficial cover crop in potato rotations since it promotes total soil fungal biomass and diversity and presumably a healthier soil, and at the same time can limit the proliferation and abundance of some potato pathogens in the soil.