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Managing tall fescue toxicosis

By Adam Speir
Madison County CEC

Tall Fescue is a forage workhorse for livestock producers from north Georgia to New England. It is a cool-season perennial grass that is tolerant of many conditions, covers more than 1 million acres north of the Fall Line, and supplements bermudagrass pastures for many livestock producers from fall through spring. Despite the important niche that tall fescue fills, there are important

Photo by Carole Knight

downsides to consider when grazing livestock on tall fescue grass.

The problems associated with livestock grazing tall fescue are generally referred to as “Fescue Toxicosis.” This term describes a host of potential issues that can include reduced conception rates, decreased weight gain, decreased milk production, constricted blood flow (especially to extremities), elevated blood temperature, poor heat tolerance, holding of winter coat in the spring, and excessive nervousness. These symptoms are caused by a fungus that lives inside the plant tissue. This fungus is referred to as an endophyte and is toxic to all livestock because of the production of ergot alkaloids, a mycotoxin (If you’re a history buff, you would enjoy researching the role ergot alkaloids have played in history). Kentucky 31, the most common fescue in Georgia, contains the toxic endophyte (E+) which produces these mycotoxins. When Kentucky 31 was first planted, the issues related to this fungus and fescue toxicosis were not known. Decades of research went into determining the causes of these issues. It was USDA researchers in Georgia in the 1970’s that first determined these harmful problems livestock were having while grazing tall fescue was caused by a fungus inside the plant.

While the fungus inside the plant causes detrimental impacts to livestock, it actually helps the plant tolerate stress, which is what initially made it such an appealing forage species. Researchers learned that the fungus is present in fescue seed, and heating the seed or storing it for more than a year could neutralize the endophyte (E-). Unfortunately, the breeding of E- fescue resulted in plants that were not tolerant of grazing, drought, or heat and many stands failed. Later discoveries of non-toxic, “novel” endophytes (NE) by researchers in New Zealand led to breeding of tall fescue varieties more stress tolerant than E- varieties and did not have negative effects on livestock that E+ fescue did.

The question for livestock producers is how to best manage the impacts of fescue toxicosis given the production costs to operations. Should producers look to renovate all of their pastures with NE varieties of fescue, utilize other forages, or are there other options that producers can implement to mitigate the risk and damage of fescue toxicosis?

Toxic Fescue Rotation – Producers might be able to manage current stands of E+ tall fescue by understanding the nature, timing, and location of the toxic endophyte within the plant. As mentioned, the fungus is present in the fescue seed. As the seed germinates and the plant develops, the endophyte infects the plant at the base of the leaf. When the plant begins its reproductive cycle, the endophyte moves into the plant stems and eventually the endophyte moves from the stem into the developing seed head and seeds. Producers should time grazing of E+ tall fescue to avoid seed heads and plants that are in reproductive stages of development to reduce the concentration of endophyte toxicity.

Producers should also not graze tall fescue during summer months for several reasons. First, tall fescue is a cool season grass and summer can be stressful for the plant, especially hot, dry summers. Second, the negative effects of tall fescue include hampering an animal’s ability to tolerate heat. Animals will want to spend all their time in shade or water and not grazing. Third, high temperatures have been shown to intensify the toxic effects of the endophyte. Producers should plan to include warm season perennial or annual grasses to accommodate removing animals from tall fescue the entire summer.

Tall Fescue Dilution – Producers can dilute the negative effects of toxic fescue by diluting it with other forages, especially legumes. White clover has been shown as a good option for interseeding into toxic fescue stands in Georgia. This mix can reduce the overall intake of toxins by animals selectively grazing the clover which improves overall animal performance. Also, the higher forage quality of the clover will improve the overall forage quality of the stand, also leading to improved animal performance. If you’re looking to interseed legumes in fescue, consult with your County Extension Agent to determine the best course of action.

Seedhead Suppression – Some research has been done in Kentucky and Missouri and demonstrations in Georgia using herbicides to suppress seedhead development in tall fescue and reduce toxicity. Studies have shown an increase in conception rates with cattle on herbicide-treated pastures compared to untreated fescue pastures. While use of herbicides such as Chaparral will suppress fescue seedheads, as well as control broadleaf weeds, the metsulfuron will stunt fescue, causing it to yellow and reduce overall yields which ultimately reduces stocking density. The potential tradeoff in lower stocking density is the increase in weaning weights and production. Still more work is needed in looking at the long-term impacts of this strategy on tall fescue, but you can get more information on this approach from you County Extension Agent.

Tall Fescue Replacement – Ultimately, the best long-term strategy for tall fescue management is replacing it with NE fescue varieties. Honestly, this can be a labor-intensive and a time-consuming process not without risk of failure, as is with any new establishment. To replace existing stands of tall fescue, follow a “spray-smother-spray” method. First, prevent seedhead development by mowing at least twice prior to spraying. Spray an infected field with a heavy rate of an effective herbicide such as glyphosate in the spring, growing a smother crop, usually a warm-season annual grass such as pearl millet, in the summer, and then spraying any surviving tall fescue plants and weeds again in the fall with another heavy rate of herbicide before planting the new fescue variety.

Another option – the “spray-spray-plant” method, might be more feasible for smaller producers. You prevent seedhead production in the spring as in the first method, then spray herbicide in late summer and again four-six weeks later followed by planting the new fescue within one day of the second herbicide application. It’s best recommended to seed the new variety from mid-September to late October at 15-20 lbs. per acre.

Tall fescue definitely has a place in the forage systems of north Georgia and many livestock producers utilize it as part of their systems. Producers should look into the potential impact it’s having on their livestock and possible ways to reduce the damage of fescue toxicosis. You can find more information on the Georgia Forages website, your local county Extension office, or in UGA circular 861 titled “Novel Endophyte-Infected Tall Fescue.”