In 1943, Kentucky released a hardy pasture grass that farmers embraced; today, tall fescue covers an estimated 35 million acres, while its hidden fungus causes costly cattle health problems

Imagine a single grass seed, accidentally collected from a steep hillside in Kentucky in 1931, which would go on to carpet an area the size of Illinois. This is the remarkable tale of the tall fescue grass, and the influence it continues to have on our daily lives. Tall fescue itself had already been growing in the eastern U.S. for over a century by the 1930s; what happened in 1931 was that University of Kentucky agronomist E.N. Fergus spotted an unusually hardy strain of it on a Menifee County farm. He collected seed from the patch, tested it through the decade, and the resulting variety was finally released to farmers in 1943 under the name “Kentucky 31,” according to a 2025 University of Kentucky article. Within 20 years, it had become widely used across the eastern U.S., and it remains so almost a century later.

A humble discovery that took over the countryside

While Kentucky 31 may not have been a glamorous find, it was certainly useful. The grass was exceptionally resilient to drought, poor soil quality, overgrazing, and harsh winters. These qualities proved to be invaluable to farmers seeking to provide a steady source of pasture for their livestock, and the plant's reputation quickly preceded it. By the 1960s, tall fescue had become the dominant grass species in what researchers call the "Fescue Belt," an agricultural region stretching from the Midwest to the South. To this day, it remains one of the most widespread cool-season grasses in the country.

What may come as a surprise is that the same qualities that make tall fescue such a coveted crop also make it exceptionally dangerous to livestock, and that has nothing to do with harsh winters. The reason for this lies in a certain fungus, Epichloë coenophiala, which thrives in the tissue of the plant, undetectable to the naked eye, a 2014 peer-reviewed study titled “Characterization of Epichloë coenophiala within the US: are all tall fescue endophytes created equal?,” published in Frontiers in Chemistry, explains. While this particular strain of endophyte, as it's called, can be particularly useful in giving the grass its disease-resistance properties, it also produces several harmful alkaloid compounds that proved poisonous to animals.

A billion-dollar issue lurking in tall fescue

This isn't just an issue of animal welfare, either. According to a USDA Agricultural Research Service report, over 80 percent of tall fescue in the Transition Zone is infected with this endophyte, leading to "fescue toxicosis," a condition that affects cattle and other animals grazing on the plant, with severe economic consequences for farmers. Fescue toxicosis shows up as reduced weight gain and impaired reproduction, along with trouble regulating body temperature: the alkaloids cause the animals’ blood vessels to constrict, which restricts blood flow to the skin and limits their ability to shed heat: a problem that can be compounded by reduced sweat-gland activity. This leads to a reduction in overall beef production, which in turn leads to higher prices for consumers, who are ultimately responsible for footing the bill.

Why a 1940s-era pasture grass affects you

The next time you hear about regenerative agriculture, or notice a jump in beef prices at the grocery store, keep in mind that one of the culprits may be this humble blade of grass. Fescue toxicosis and its effects on the agricultural economy are an issue that goes far beyond the farm, and one that scientists have been working to solve for almost 50 years. Researchers have worked to breed new variations of tall fescue that exclude the harmful properties of the Epichloë coenophiala endophyte, while retaining its beneficial qualities.

These include "improved persistence" and "heat tolerance," qualities desperately needed in a changing climate. One such variety, developed by University of Kentucky plant breeder Tim Phillips using a non-toxic “novel” endophyte and named for longtime UK forage researcher Garry Lacefield, is now marketed as “Lacefield MaxQ II.” It has shown promising results, but widespread conversion to this new type of grass would require replanting already-existing pastureland, and the resources required would be neither swift nor cheap.

A lesson in plant biology, wrapped in a grass seed

One small plant seed changed the agricultural landscape of the eastern United States, and tall fescue is a reminder that such sweeping changes often come at a price. The resilience that makes it such a desirable crop also makes it a menace to livestock, and the search for a solution continues to this day.