Technical Abstract: Neotyphodium infected tall fescue produces a variety of secondary metabolites that are toxic and/or grazing deterrents. Alkaloid production has been related to defense against vertebrate and insect pests, in particular plant-parasitic nematodes. The ergot and pyrrollizidine (loline) alkaloids are the major defensive toxins produced in the Neotyphodium-tall fescue grass association. Using a migratory endoparasitic nematode, Pratylenchus scribneri as the target organism, sterile in vitro motility bioassays were conducted to detect possible toxicity when this species is exposed to ergovaline tartrate, an ergopeptide alkaloid, and N-formylloline (NFL), a festucine alkaloid. Preliminary studies suggest that ergovaline tartrate is more acutely toxic to P. scribneri at low concentrations than NFL following a 24-hour time exposure. For example, at a specific concentration N-formylloline requires an exposure time of 96 hours to cause a similar 100% mortality to the nematodes as ergovaline. However, both alkaloids were nematotoxic as motility was not recovered when the solutions were replaced with water.