"Endophyte" refers to a fungus that lives within the fescue plant, meaning it cannot be seen with the naked eye. The endophyte found in tall fescue is beneficial to the plant: It gives tall fescue insect resistance, enhanced grazing tolerance, and greater persistence in stressful environments. The major disadvantage of some of the endophytes of tall fescue is that they produce toxic alkaloids that have detrimental effects on many types of livestock.