"Tall fescue has been widely accepted as a forage plant. It is particularly well adapted to the southern portion of the cornbelt where it has been planted on millions of acres of pasture lands. Despite its unique adaptation to this area, various animal production problems are connected with fescue."--First page.Jimmy C. Henning (Department of Agronomy) and Einar Palm (Department of Pathology, College of Agriculture)Revised 2/88/6

Henning, Jimmy C.

Palm, Einar

English

University of Missouri: MOspace

The fescue fungus problem Jimmy C. Henning Department of Agronomy and Einar Palm, Department of Pathology, College of Agriculture JUti Z 9 1 (l-, Tall fescue has been widely accepted as a forage plant. It is particularly well adapted to the southern portion of the cornbelt where it has been planted on millions of acres of pasture lands. Despite its unique adaptation to this area, various animal production problems are connected with fescue. The four major animal production problems asso-ciated with fescue are: summer slump or syndrome, fescue foot, fat necrosis, and agalactia (little or no milk). Many ideas and theories have been advanced as to the causes for these problems, but until recently little progress had been made in solving them. In the late 1970's, researchers from Auburn Uni-versity reported a high occurrence of a fungal endo-phyte in farmers' pastures where cattle had symp-toms of the summer slump syndrome. Cattle grazing fescue pastures that did not contain the fungus appeared to perform normally. The fungus found growing inside the fescue plant was first named Epichloe typhina but is now called Acremonium co-enophialum by many researchers. Because it grows inside the fescue plant, it is also referred to as the endophyte fungus. Since that time, many research projects have linked the endophyte fungus with low animal performance, especially noted during the sum-mer months, and hence the name, summer slump or syndrome. However, when animals consume fungus-infected fescue during any time of the year, performance is not as high as when fed uninfected fescue. The drop in performance just isn't as great nor as noticeable during the warmer summer months. While it is generally accepted that there is a positive association between the fungus-infected fes-cue and the summer slump syndrome, the exact relationship is not known. The fungus may stimulate the fescue plant to produce substances that cause low animal performance, or it is possible that the fungus 4599 Endophyte fungus growing between the cell walls of a fescue plant. This fungus is responsible for the summer slump of cattle grazing fescue. itself may have a direct effect on the animal. Of the four animal disorders associated with tall fescue, the only one positively associated with fungus is the summer syndrome. The symptoms of this disorder are rough hair coats, high rectal temperatures, poor performance, panting, low feed intake, excessive salivation and low prolactin levels which bring about lowered milk production. These animals seek shade and like to stand in water and mud. Summer syndrome is also related to low conception rates. The problem The toxic substance can also be found in hay even after several years of storage. It is higher in the stems, seed and seed heads than in the leafy parts of the plant. Hay may still be toxic after three years of storage. The University of Kentucky conducted a study in which toxic forage was fed to animals under con-trolled temperatures. Animals in rooms maintained at 90 to 95 degrees F deyeloped all of the classic symptoms of summer toxicity while those in rooms with temperatures of 68 to 71 degrees F or SO to 55 degrees F developed none of the visible symptoms at all! The researchers concluded that this experiment demonstrated that the poor performance of animals Archive vrsion - cck for udatesfed toxic fescue was associated with high tempera-tures and not the increased concentration of some toxic substance. Generally speaking, better animal performance is achieved on known toxic fescue fields with a legume present than when it is absent. Whether this is brought about by reduced intake of the fescue or by _a compound in the legume that counteracts the toxic substance is unknown. The fungus is seed-borne, and it is through the seed that it is spread. Plants do not become infected from adjoining infected plants. As an infected seed germinates, the fungus grows into the new seedling plant and becomes established. This is apparently the principal means by which the fungus is introduced into a field. There is little or no evidence that it is transmitted by insects or other carriers. How the fungus lives and grows It is not possible to look at a fescue plant ~i~h the naked eye and determine whether that plant 1s mfect-ed with the endophyte. The fungus grows and exists within the plant and should not be confused with ergot, (a disease) sometimes found in the seed head of fescue and other grasses. The endophyte of tall fescue grows within the intercellular spaces of the plant. When portions of the plant are processed, stained and placed under the microscope, the hyphae of the fungus appear coarse, contorted, sometimes coiled, mostly unbranched, and run vertically between the host cells . The fungus appears prominently in leaf sheaths in early spring and fall. Later in the season, the fungus grows up into the flower shoots and into the seed. The endophyte is an internally seed-borne organism. It is found between the aleurone and endosperm layers of the seed. When infected seed is planted, the growth of the fungus is usually not detected until the plants are four to six weeks old. It is not found in the root system and only occasionally in the rhizomes. W~en the plant is dormant and during the early vegetative stages, the fungus can be found in the tissue of the apex. When the plant begins to form flower ~hoots and stems, the fungus begins to concentrate m the intercellular spaces near the growing point of the stem and reaches its greatest density in the tissue of the side branches of the flower head. It is found in the leaf tissue only in the sheathing base up to the end of the ligule and not in the tissue of the expand-ed leaf blade. Not being present in the leaf blades may explain why there are fewer symptoms of fes~ue toxicity during the early spring and late fall grazmg seasons. At these times, the ratio of leaf blades to other plant portions is quite high . Evidently, the fungus is not capable of penetrat-ing living fescue cells, and its only mode of entry into the plant is through the seed. Managing the fescue endophyte problem There are several practical measures you can take to reduce the losses occurring from feeding endophyte-infected fescue. 1. Destroy infected fields and reseed . 2. Develop a grazing system. 3. Incorporate legumes . 4. Avoid grazing mature fescue. 5. Feed toxic fescue during cool weather. 6. Avoid making hay from infected fields. 7. Avoid heavy nitrogen fertilization of infected pastures. Destroy infected fields and reseed. Severely infected fields that have had a history of toxicity may need to be destroyed and reseeded with clean seed. If a field can be cropped for two or three years, the procedure is relatively easy. In some places in Missouri, it may not be simple. Research by USDA-ARS-UMC Agronomy Depart-ment scientists has demonstrated that fescue renova-tion is neither simple nor inexpensive . Studies have shown that paraquat (Gramoxone Super) or glyphosate (Roundup) alone are not e~fec-tive in killing tall fescue. Preliminary observations have revealed that herbicide application plus the use of a summer interim crop increases the chances of a successful fescue kill. The key principles appear to be: I. Application of labeled herbicides to short, ac-tively growing tall fescue according to label instructions. 2. No-till planting an interim crop during the sum-mer following herbicide application to further stress the sod. 3. Spreading the eradication process over 2 grow-ing seasons, allowing time to evaluate fescue kill 6 to 9 months after last herbicide applica-tion. An example rotation might be: Year 1 Spring Prevent seed production. Summer Graze hard to weaken sod . Fall Spray herbicide according to label. Year 2 Spring Follow up herbicide spray if accord-ing to label sequence or if signifi-cant amounts of fescue survive . May No-till summer annual such as sudangrass. August Harvest sudangrass and evaluate fescue kill. Repeat herbicide ap-plication if necessary. Fall Let lie fallow or plant winter annual such as wheat. Table 1. Effect of clover and time of year on ADG of steers grazing infected fescue.* Fescue - Fescue - Fescue -no legume 13% trefoil 24% ladino clover Spring & early Summer grazing Fall grazing 'Auburn University 0.86 lbs. 1.26 Year 3 Spring Evaluate fescue kill. Harvest/graze wheat early if nec-essary. No-till fescue. It is critically important to realize that no method has been proven 100 percent effective at this time. Any attempts to kill fescue by means other than till-age must be made with caution and patience. Fescue should be treated like the persistent perennial that it is. Develop a grazing system. If a farm has only one or two fields with serious problems, it may be practical to adjust various practices. A good management practice is producing hay or other grass species (e.g. orchardgrass, brome, etc.) and legumes on the farm, so that the entire animal diet is not fescue. Yearly diets consisting principally of infected fescue may become accumulative in the cattle. During the summer months, avoid grazing infect-ed fescue fields as much as possible. When it is necessary to graze them, do not pasture them for extended periods. Graze only for about a week, and then move the cattle to other pastures for at least two weeks. There are implications that the toxic effects from endophyte-infected fescue may be accumulative. Cat-tle eating infected fescue seed heads early in the grazing season may ingest large amounts of the toxic substance and are more likely to show illness. Plan-ning a grazing system takes time, but it will pay off in animal performance. Incorporate legumes into the fescue. Incorporating legumes into the fescue has a positive diluting effect. Even small amounts of ladino clover have increased gains and conception rates, according to Missouri research. Just incorporating legumes into highly infected fescue fields may not overcome toxicity problems unless you use proper management techniques. The fields should always be intensely grazed early in the season. At this time, the heavier grazing pressure will usually be more detrimental to the grass than to the legume. When the grazing pressure is reduced, the legumes will become more dominant in the stand during the late spring and early summer. When air temperatures are cooler, the effects of the endophyte are not as pronounced on livestock performance as 1.50 lbs. 1.51 1.65 lbs. 1.41 when temperatures exceed 80 degrees F. (See Table 1) Avoid grazing mature fescue. Never let cattle graze seed heads of severely infected fescue. Destroy seed heads as quickly as possible. The fungus is more concentrated near the flowering seed heads as the plants mature. Use a rotary mower to clip the seed stalks as soon as they extend above the rest of the growth. Research at Auburn University showed that steers fed fungus-infected fescue seed had extremely low gains as compared to steers fed non-infected seed. The average daily gain (ADG) from the intake of 9.1 pounds of infected seed was 0.44 pounds as com-pared to 2.11 pounds ADG when 14.1 pounds of non-infected seed were consumed. Feed infected fescue during cooler times in the year. Highly toxic tall fescue pastures should be used mainly during the cooler times of the year, especially the fall and early winter months. Cattle are affected less by the endophytic toxins during cooler tempera-tures. Avoid making hay from infected fields, if possible. Although the summer slump symptoms are not as visible during the winter, fungus-infected fescue hay will reduce animal performance. Animals fed infect-ed fescue hay may be more susceptible to the summer syndrome the following spring and summer. The incorporation of legumes in the hay improves cattle performance. Also, animals fed infected fescue hay during all or part of the winter may develop summer syndrome more easily than other animals. Avoid heavy nitrogen fertilization of infected tall fes-cue. · Georgia research has shown that high nitro-gen fertilization greatly increases the toxin level in tall fescue. Use legumes as the nitrogen source in infect-ed pastures as much as possible. Although legume nitrogen ½:ill stimulate toxin formation like fertilizer nitrogen, the legume will dilute the overall toxin intake. Determine the severity of the problem in a pasture program. There is considerable disagreement about what percent of fungal infection constitutes an eco-nomic threshold. Some workers believe that it is 20 percent; others say 25 to 40 percent. Because the percent of infection in plants does not always reflect the severity of the toxicosis, it would appear that seed for new seedings should contain less than 5 percent infected seed. Testing samples of fescue for the fungus is a sure way to determine what percent of the fescue plants in a pasture is infected. (See "How to Test" for details on taking samples .) Observing animals can be helpful in determining the degree of the problem. Fields with a known history of poor animal production are likely candi-dates for high levels of infection. Obtaining seed New varieties. Many of the newer varieties may be certified as relatively (less than 5 percent) free of fungus . However, just the fact that it is a new variety does not necessarily ensure that it is free of the fungus unless it is so certified. New varieties that are available or soon will be include MO-96, Kenhy, Forager and Johnstone. These varieties have been relatively free of the fungus and in some cases may be certified free . There is some common Ky 31 available that may also be certified free of the fungus . Another new variety is Triumph, but it is not winter hardy in Missouri. Aging of seed. Aging infected seed is another way to obtain seed that will produce fungus-free plants. Aging the seed reduces the viability of the fungus. Researchers at Auburn University found that seed 88 percent infected was reduced to 15 percent after 12 months of storage. However, research at the Universi-ty of Missouri did not find quite so rapid a decline in the viability of the fungus . A practical application of these research findings is that seed (common or non-certified fungus free) should be at least two years old before replanting a fescue field . Treating seeds. Both chemical and non-chemical seed treatments have been evaluated for eradication of the eridophyte from infected seed. Hot water treatment has been successful in eradicating the endophyte. Take care so that high temperatures do not severely reduce the germination percentages. Generally, hot water treatment is successful if the seed is pre-soaked for six hours at 90 degrees F, followed by 20 minutes at 140 degrees F. Chemical seed treatments using Bayleton and its analog Baytan (Mobay) have been effective fungi-cides. There were some reductions in germination from the seed treatment fungicides. However, in most cases, reductions will not be significant. How to test Check for infection. The decision to test can be a difficult one. There would seem to be no reason to test a pasture with a history of poor animal per-formance . Research has shown that these fields are most certainly infected. Another problem is that the percent of infected s-1 I Figure 1. Areas with the plant where there are usually concentrations of the endophyte fungus (indicated by arrows). A. stem. B. leaf sheath up to the ligule. C. spike-let and seed head. plants may not reflect how animals will perform on that particular pasture. In other words, the percent of infection may not be correlated to the intensity or severity of the toxin. To test, obtain seed samples collected from har-vested seed lots by taking small samples from several bags or from a number of places in a seed lot. Mix these small samples, and then send a 2-ounce com-posite to the testing center. Also, collect tissue samples from random areas within the field . The diagnostic center suggests tak-ing four or five samples per acre. The total sample should represent about 10 acres of a pasture. Because the fungus has not been found in the roots or outer leaves, don't include these in a tissue sample. Take the individual samples from the leaf sheath, starting just above the ligule and down 2 or 3 inches from where it is wrapped around the stem. Early in the growing season, collect the sample from sections in the flower stem. At that time of the year, the tissue sample may also be taken from the spikelet stem. Do not take the test too early in the year. Wait until the stems have elongated and are at least 12 inches tall. If samples are to be tested, get materials and instructions at your local extension center. Send sam-ples to the Livestock Nutrition Laboratory, P.O. Box 1653, Columbia, MO 65205 Other disorders associated with tall fescue The summer slump syndrome is the only disorder that is definitely linked to the endophyte fungus. It is possible that fescue foot, fat necrosis and agalactia may also be associated with the fungus, but at this time the evidence is only circumstantial. ■ Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914 in cooperation with the United States Department of Agriculture. Gail L. Imig, Director, Cooperative Extension, University of Missouri and Lincoln University, Columbia, Missouri 65211. ■ An equal opportunity institution. 4599 Revised 2/88/6M 

The fescue fungus problem

https://mospace.umsystem.edu/xmlui/bitstream/10355/77870/1/G04599-1988.pdf

The fescue fungus problem

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