The issue stated in the title is of great concern to many livestock producers who grow tall fescue for forage, and for good reason; it has profound economic implications. This question first began to be raised when endophyte-free (fungus free) fescue became commercially available, and it continues to come up today as many producers are planting, or considering planting, "novel endophyte" fescue.

Here is a bit of background about fescue. In the late 1970's it was learned that an endophyte (fungus) grows inside most fescue (the vast majority of which is the variety 'Kentucky 31') used for pasture or hay in the USA. This fungus produces toxins that upset temperature regulation in the bodies of grazing animals, sharply lower weight gains, and can reduce reproductive performance. The economic loss to the beef industry alone in the USA is estimated to be over $600 million annually.

In the early 1980's, endophyte-free fescue seed began to be readily commercially available. Animal performance on this fescue was far better, but it was quickly found that endophyte-free fescue is much less stress tolerant than endophyte-infected fescue. As a result, it is difficult to maintain stands of endophyte-free fescue over time, especially in hot and periodically dry climates such as occur in the Deep South.

Research has shown that the fescue fungus does not move from plant to plant; it is transferred only in seed. Thus, whether or not a plant is infected depends entirely on whether or not the seed from which the plant arose was infected. It is also known that the fungus does not move in fescue pollen. Therefore, although fescue pollen is wind-transferred, pollen does not result in endophyte fungus transfer. However, some producers who planted endophyte-free fescue seed found that after a few years they had fescue stands that were mostly endophyte-infected, and the performance of their livestock was once again negatively affected. How could this have happened?

There are two possible scenarios. One is that if there had already been a stand of infected fescue in a field, the fescue plants may not have all been killed before endophyte-free fescue was planted. Sometimes a herbicide treatment is not 100% effective in killing a stand of fescue, and tillage is even less reliable.

The other possibility is that endophyte-infected fescue seed containing viable endophyte was in the soil when endophyte-free seed was planted, or that such seed were introduced sometime thereafter. Regardless of the source of the toxic fescue, where there was a mixed stand of endophyte-infected and endophyte-free plants, the infected plants were often able to eventually dominate due to greater seed production, better seedling vigor, and more tolerance to drought and other stresses.

Beginning in 1999, "novel endophyte" fescue seed became commercially available. This refers to fescue that contains a research-identified strain of fungus that does not produce the toxins that lower animal performance, but that does impart stress tolerance to plants. The first such product that became commercially available in the USA is sold under the name "Max Q." Many research studies and on-farm plantings have proven that the weight gains and reproductive performance of livestock grazing this new novel endophyte fescue is as good as that of animals grazing endophyte-free fescue, and that stands are highly persistent. However, some producers are understandably still concerned about invasion by "toxic" endophyte-infected fescue.

Assuming all existing fescue plants were killed and no viable toxic endophyte seed were in the soil at planting, the only way a novel endophyte stand could become contaminated with toxic fescue plants would be if toxic seed were somehow introduced into the field. Wild animals, birds, and wind have not been found to cause seed movement problems. Evidence of this is that at the Black Belt Research and Extension Center at Marion Junction, several endophyte-infected and endophyte-free paddocks have existed side-by-side for over 15 years with no spread of toxic endophyte-infected plants into the endophyte-free fields.

However, moving livestock directly from a pasture where animals have been eating toxic fescue seedheads into a novel endophyte fescue field could result in some transfer of seeds within their bodies. Research has shown that a small percentage of fescue seed can survive an animal's digestive system and, with the seed being deposited in the new fescue field in manure (which could occur within 3 days of being consumed), a suitable situation for germination and establishment could result. An even greater risk of of introducing toxic fescue would occur if a producer fed toxic endophyte-infected hay on a novel endophyte fescue sod. If such hay contained toxic fescue seed, the animals being concentrated around the hay would "plant" the seed and simultaneously suppress the existing fescue, resulting in high probability of stand contamination.

Conclusion

In hot, sometimes dry climates such as occur in the Deep South, the endophyte status of an endophyte-free fescue stand can change. However, this is not due to endophyte-free plants becoming infected. It is because toxic endophyte-infected plants in the stand (either plants that were not killed when the endophyte-free fescue was established or that arose from toxic fescue seed that were in the field at planting or that were introduced later) out-reproduced and outcompeted the endophyte-free plants.

The keys to obtaining a novel endophyte stand that is free of toxic endophyte plants are to prevent toxic fescue plants in the field to be planted from making seed during the establishment year, and to make certain that all existing toxic fescue is killed before planting. The key to maintaining a stand free of toxic endophyte-infected fescue is to avoid introducing toxic fescue seed. This requires removing livestock from a headed toxic fescue field at least 2 days before moving them to a novel endophyte stand, and by refraining from feeding toxic fescue hay in the newly planted field. By following these simple steps, an essentially pure novel endophyte stand should be obtained and, since novel endophyte fescue has proven to be quite competitive, it should remain so indefinitely.