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Tall fescue (Festuca arundinacea) cover crops, when infected with the endophytic fungus Neotyphodium coenophialum, have been reported to reduce plant-parasitic nematode populations in some cases but not others. During a 2-year study endophyte-infected Kentucky-31 was compared with endophyte-free Star Grazer under greenhouse and field conditions. The endophyte-mediated suppressive effect was evaluated on four plant-parasitic nematode genera, nematophagous fungi and predacious nematodes. Sprinkle plate and most probable number assays were utilized to evaluate the population dynamics of nematophagous fungi across treatment groups. N. coenophialum infection was periodically evaluated using a Tissue Print Immunoblot Assay. Significant suppression of Pratylenchus crenatus (P < 0.05) by endophyte-infected F. arundinacea was observed 240 days after planting (DAP) in a greenhouse study. Significant suppression of Pratylenchus crenatus (P < 0.05) was observed, at 80, 1,632, 2,934 and 3,713-degree days after planting (DDAP) in microplot experiment 1 (MP1) and at 3,744 DDAP in microplot experiment 2 (MP2). Significantly fewer (P < 0.05) P. crenatus were extracted from Malus domesticus roots under Kentucky-31 cover in comparison to Star Grazer in MP1 but differences were not significant in MP2. Suppression was observed during both field trials, but the suppressive effect of endophyte-infected tall fescue cover varied with time of stand establishment. Populations of Mesocriconema xenoplax, Xiphinema americanum, Paratylenchus projectus, predacious nematodes and nematophagous fungi did not vary significantly (P ≥ 0.05) as a consequence of endophyte-infected F. arundinacea cover. Shoot/root tissue extract and leachate exposure, comparing Kentucky-31 against Star Grazer, immobilized Pratylenchus spp. in some case but not others. Direct exposure to N-formyl loline produced no effect on Pratylenchus spp. or X. americanum survival. Species-specific feeding responses to endophyte-infected and endophyte-free F. arundinacea produced no significant (P > 0.05) differences in population densities among Pratylenchus penetrans, P. scribneri or P. brachyurus.