During the past ten years years or so, there has been a great deal written and said about the fungus (Acremonium coenophialum) which often grows inside tall fescue plants. In fact, there has been so much publicity regarding this fungus that it is hard to imagine that any livestock producer in the areas where this grass is adapted could not be aware of it.

Reduced Animal Performance

We now know that when this fungus is present, the weight gains of animals are typically much less than when it is absent. In several experiments conducted in various states, the gains of steers have been around 0.1 pound per day less for each 10% of fungus infection. For example, a tall fescue field in which 50% of the plants are infected is likely to result in yearling average daily gains of around 0.5 pounds less than if the fescue plants were non-infected.

Furthermore, the reproduction of cattle, sheep, and other ruminant animals is likely to be considerably lower when grazing on infected, rather than non-infected, tall fescue. This is particularly true if the animals are under nutritional stress, such as is typically the case with first-calf heifers.

Horses are particularly sensitive to the toxin(s) produced by the fungus. Mares grazing infected fescue during the latter stages of pregnancy are likely to abort, have foaling problems, produce stillborn foals, and/or produce little or no milk. Dairy cows grazing pastures having even low levels of infection have greatly reduced milk production, even though the same animals would produce as well on non-infected fescue as on ryegrass.

How The Fungus Spreads

It is therefore not surprising that many producers are interested in planting and growing non-infected tall fescue. Non-infected seed is readily commercially available. However, a critically important question which continues to arise is, "Will non-infected tall fescue remain fungus free?" The purpose of this article is to address this question.

Here is an important fact: The fungus is exclusively seed- transmitted. It is not "contagious" and does not move from plant to plant. Whether or not a plant is infected depends on whether the seed from which that plant arose was infected. However, this does not necessarily mean that the act of planting non-infected seed will result in a field which will be forever non-infected.

Sources Of Infected Seed

If infected seed somehow get into a field planted to non- infected fescue, it is certainly possible for them to germinate and become established as infected plants. If a new non-infected pasture is planted in an area which was previously infected fescue, any seed less than a year old which are already in the soil are likely to result in infected plants. This is why it is recommended that fescue which is to be re-established not be allowed to produce seed during the year of reestablishment.

In some cases, it is not the seed from old fescue stands, but rather the vegetative material from the old sod which remains alive and results in infected plants. In particular, when tillage is the primary action aimed at killing old infected sods it is possible that some of the root material will remain alive and result in infected plants. A number of Alabama forage producers have thought they had killed infected stands with tillage only to be bitterly disappointed to later learn that they had not.

Infected seed can also be introduced into a non-infected pasture in other ways. Research at Auburn University has shown that if cattle consume infected seed, some of this seed can pass throuth the animal's body, germinate, and become established as infected plants. Therefore, animals should not be allowed to graze a non-infected pasture until at least 72 hours after having grazed on an infected pasture.

In a few cases, a non-infected pasture which has an infected pasture in its watershed could have infected seed washed into it. Fortunately, there appears to be little chance that wind or wild animals are likely to introduce any significant amount of infected seed into an area. This statement is based on the fact that in some areas non-infected pastures separated from infected pastures only by a barbed wire fence have remained non-infected for many years.

Changes In Infection Level

We have now had the opportunity to monitor the fungus status of some pastures over a period of ten or more years. The finding is that non-infected pastures tend to remain non-infected, and highly infected pastures remain highly infected. However, pastures having intermediate levels of infection tend to slowly increase in infection level.

At first thought, it might seem that non-infected fescue plants are becoming infected, but this is not the case. The fact is that infected plants have more stress tolerance than non- infected plants. As a result, when they are growing together in competition, the attrition rate is higher among non-infected plants, especially in highly stressful situations. Also, infected plants tend to produce more seed than non-infected plants.

In long-term monitoring of pastures at the Black Belt Substation, pastures having intermediate levels of infection tended to increase in infection level by about 2 percent per year. This finding provides incentive to producers establishing new non-infected pastures to strive to eliminate all infected plants and to keep all infected seed out of newly-established non-infected fescue fields.

Summary

Non-infected tall fescue offers producers a great deal in terms of improved animal performance. However, there are some management concerns associated with getting, and keeping, a non- infected stand which do not apply to infected tall fescue. Non- infected tall fescue plants do not become infected, but it is possible for a non-infected field, and especially a partially infected field, to ultimately become a highly infected field.