Tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] is a cool-season, perennial grass frequently infected with the fungal endophyte Neotyphodium coenophialum. An endophyte is a fungus or bacteria that lives entirely within the tissue spaces of plants and is only visible microscopically. The plant and fungus enjoy a relationship that is symbiotic—mutually beneficial to both organisms. The fungus has free access to the plant’s nutrients and the plant provides a means for the endophyte to reproduce through infected seeds. The fungus, in turn, produces chemicals (ergot alkaloids) that function as chemical defenses, making the plant more vigorous, pest-resistant, drought-resistant, and tolerant of many adverse soil and environmental conditions. The endophyte produces a variety of ergot alkaloids, of which ergovaline is the primary concern and accounts for approximately 80 percent to 97 percent of the alkaloids in tall fescue. Ergovaline concentrations in tall fescue can range between 0-3,000 ppb (DM) with the highest concentrations in the stem and seedhead and in the bottom 3 inches of the plant. Hay from infected fields can remain high in ergovaline even when stored over several years. “Fescue toxicosis” is the general term used for the clinical diseases that can affect cattle consuming endophyte-infected tall fescue.
Arnold, Michelle; Gaskill, Cynthia; and Smith, S. Ray, "Fescue Toxicosis" (2014). Agriculture and Natural Resources Publications. Paper 169.