The Colorado potato beetle (CPB) is a serious pest of potatoes worldwide. In Washington, organic potato acreage is increasing with few cost-effective CPB control options, while conventional growers rely on broad-spectrum insecticides that may be taken off the market by changing federal regulations. Entomopathogenic nematodes (EPNs) have shown potential as biological control agents against CPB, as one component of integrated pest management (IPM). A survey of endemic EPN populations in the Columbia Basin of Washington revealed that some potato fields under organic and conventional management housed robust EPN populations. Thus, conservation or augmentation of EPNs might improve natural control of the Colorado potato beetle. I will discuss a study examining the ability of EPNs, applied at different rates, within potatoes under organic and conventional fertility. Organic fertility may support soil competitors possibly reducing EPN effectiveness. However, we hypothesize that soil properties associated with increased organic matter may sustain EPN populations over the season. Potato field plots were randomly assigned chemical fertilizer or a chicken and cow manure mixture. During the season, EPNs were applied at zero, low and high rates. EPN infection was monitored with sentinel wax worms and CPB larvae. All treatments were replicated 8 times.