Crop rotation is a major factor in maintenance of soil productivity in cropping systems, but the role of mycorrhizal fungi has been little considered. A tall fescue (Festuca arundinaceaSchreb.) sod heavily infected with theAcremonium coenophialumendophyte was plowed, and pearl millet (Pennisetum americanumLeeke) or crabgrass (Digitaria sanguinalis(L.) Scop.) was grown. Pearl millet produced more shoot dry matter and was more heavily colonized than crabgrass, and soil populations of mycorrhizal fungi were usually higher with pearl millet. Associated with the production of pearl millet and crabgrass were radical changes in the mycorrhizal fungal community. Populations of eight of 19 species decreased, four of them not detected at the end of the season. Populations of nine increased, five of them not detected at the beginning of the season. Field host and time affected species richness, dominance, and diversity; but only time affected equitability. This study suggests that crop rotation may be used to manage the mycorrhizal fungal community. Managing these fungi may be important if individual species or biotypes are found to be pathogenic or mutualistic.