The complexities of tall fescue

By Mike Rankin



Tall fescue, despite its long history as a primary U.S. pasture grass, may still be the most mismanaged and misunderstood perennial forage that we have.

The tall fescue story in the U.S. is unmatched by that of any other forage species. The twists and turns of the tall fescue tale are as compelling as a best-selling mystery novel. After nearly 85 years since the beginnings of Kentucky 31 tall fescue, the final chapter has still yet to be written, even though you'll find this forage species on over 35 million acres of U.S. pasture and hay land. It's been the focus of hundreds of research trials.

Kentucky 31 got its humble beginnings on a hillside pasture in Menifee County, Ky., in 1931. From this hillside plant population, E.N. Fergus at the University of Kentucky developed and ultimately released Kentucky 31, a superior performing variety that found its way across millions of acres in the lower Midwest and large portions of the South.

Over time, it became clear that animal performance on tall fescue was erratic, at best. It wasn't just a matter of poor gains or milk production, animals suffered from lameness, high body temperature, reproductive inefficiency and a myriad of other chronic conditions. These maladies were given such terms as “fescue foot” and “fescue toxicosis.” It was in the 1970s when the source of poor cattle performance was identified as being an endophyte fungus contained within the plant. The fungus produced ergot alkaloids, which were found to be the culprit in terms of reduced livestock performance and health issues.

Once the problem was identified, two things happened.

First, the introduction of “endophyte-free” varieties offered hope of solving the issue. As these new varieties were established, it quickly became clear that while the endophyte fungus hurt animal performance, it also helped plant performance and persistence. It was a protection mechanism for the plant against pests, also providing stress tolerance. Quickly, and to the dismay of all involved, it became clear that these new “endophyte-free” varieties were not the answer.

Not to be deterred, researchers identified what are now called “novel” endophytes. These novel endophytes provide plant protection, yet do not cause the negative animal effects associated with Kentucky 31 and older variety types. As of today, several breeding companies are releasing novel endophyte varieties.

Throughout this time period of endophyte-free and novel endophyte variety development, there was also another track being taken by both researchers and farmers — figure out a way to manage around the negative performance effects of tall fescue without killing and reseeding existing stands. Developed strategies include:

  • Keep tall fescue pastures from developing seedheads, which contain a higher concentration of the endophyte fungus. This can be done mechanically by clipping, aggressive rotational grazing or more recently with applications of Chaparral herbicide.
  • Dilute tall fescue by interseeding other types of grasses or legumes.
  • Dilute tall fescue by offering other feedstuffs such as soybean hulls.
  • Look for or establish alternative pasture options during the heat of summer when toxicity effects are greatest.

Today, even with novel endophyte varieties available, there are still millions of fescue acres infected with the toxic endophyte fungus. Estimates of livestock losses run into the hundreds of millions of dollars per year. Ironically, novel endophyte varieties have gained great popularity in the North, where there are other cool-season grass options. Livestock producers have found the novel varieties to be a favorable companion grass for conventionally harvested alfalfa and as a primary grazing grass, especially on grazing-based dairies.

It's probably unrealistic to think that the millions of acres of Kentucky 31 tall fescue will all be killed and replanted, but more should be than is currently the case. Furthermore, every farm needs to be doing something to mitigate the negative effects of the toxin even if stands are not being reseeded. Whether this eventually happens or not remains to be seen — and that’s where this story continues.