After the discovery of Asian soybean rust in North America, the widespread use of broad spectrum fungicide in soybean is likely. This study, with in vitro and field components, focuses on determining if fungicides impact fungal pathogens of soybean aphid, Aphis glycines Matsumura. In vitro studies indicate that strobilurin fungicides significantly depress mycelial growth of an aphid-pathogenic fungus, Conidiobolus thromboides, at concentrations of 0.01 ppm – 1 ppm. Other fungicides also affect C. thromboides such as chlorothalonil (100– 10,000 ppm) and tebuconazole (0.1 ppm – 10 ppm). There is also evidence that germination rates of conidia of C. thromboides are negatively affected when exposed to these fungicides. In field studies conducted in 2005 and 2006, soybean aphids were collected from fungicide treated plots at two locations, and the prevalence of fungal mycoses was assessed weekly using a bioassay. An epizootic was observed late in the season (25 Aug - 5 Sep) at one location (Lamberton, MN) in 2005. Prevalence of mycoses in fungicide treated plots was significantly reduced (t=6.477, df=8, p<0.001), averaging only 11% of the untreated control. Enzootic disease was recorded at Lamberton in 2006; however, low prevalence prevented significant treatment effects. Although fungicides lowered disease prevalence in soybean aphid in 2005, there was no population response by soybean aphid. However, lowered disease prevalence in late summer may lead to a higher proportion of uninfected fall migrants colonizing buckthorn, their primary host, where epizootics are known to occur more frequently.