A pathogenic fungus (Neozygitessp.) caused dramatic reductions in spider mite populations in artificially infested soybean plots in both 1987 and 1988. Buildup of the pathogen occurred for approximately two weeks, with the most devastating epizootic infecting 100% of living mites sampled and reducing mite intensity up to 95% over a six-day period. Fungal activity was very dependent upon environmental conditions, with spread of the disease occurring only during sustained cool and humid weather. Thick-walled resting (overwintering) spores were found in 7.8% of all mites sampled late in 1988. This is the first study in the Midwest to show thatNeozygitessp. can overwinter away from its host. The impact of fungal epizootics on spider mite management is also discussed.