Karnal Bunt in Texas Wheat Dr

Texas Agricultural Extension Service The Texas A&M University System Karnal Bunt in Texas Wheat Dr. Travis Miller Historical Information sion that several states in the southeastern U.S. were posi- In the spring of 1996, Karnal bunt (Tilletia indica Mitra) tive for Karnal bunt. This led APHIS to go to the stan- was found in a sample of durum wheat seed in Arizona. dard of finding one or more “bunted” kernels in a 4 pound Subsequent investigation revealed that Karnal bunt had sample as the definitive test for the disease. been distributed in durum wheat planting seed, and that it was widespread in Arizona and New Mexico, and found The USDA-APHIS maintains a comprehensive web site in limited regions in California and Texas. Following this on the disease at: http://www.aphis.usda.gov/karnalbunt/ discovery, movement of wheat and wheat equipment was Refer to this site for more details on the disease including quarantined in the entire state of Arizona, parts of New color photographs. Mexico and California, and in El Paso and Hudspeth counties of Texas. A national survey was initiated over Disease Characteristics the next two years, with samples of wheat being submit- Upon infection, the bunt does not generally affect an en- ted from most of the wheat producing regions of the U.S. tire kernel. Typically, only a portion of a kernel, starting This survey found an infestation in San Saba County in at the embryo end, is blackened or “bunted” and eroded 1997 in hard red winter wheat, which was the first ever with a mass a mass of black spores with the offensive detection in this class of wheat. odor. Although Karnal bunt and common bunt or stinking bunt have a similar “fishy” Infested fields were quarantined for a pe- odor, they differ in that the common bunt riod of 5 years, and around each field for typically decays the entire infected kernel. a radius of 3 miles, a regulated area was Karnal bunt seldom effects yield and usu- established in which all wheat is examined ally effects less than 1 per cent of the ker- in the field before delivery to an elevator. nels in a field while infested kernels have In quarantined fields, wheat, durum wheat an objectionable “fishy” odor they are not and triticale may not be planted for a pe- usually detected in finished wheat prod- riod of 5 years, which is the estimated lon- ucts until infestation levels reach about 3%, gevity of bunt spores in soils. which is an extremely high level for field infestations. Most of the early survey was conducted by examination of fungal spores from Karnal bunt is relatively weak as far as wheat samples by a light microscope. crop damage compared to wheat diseases Spores of the Karnal bunt fungus have a common to the Texas crop or to other size and surface markings which allow lab smuts and bunts that are common in the workers to distinguish them from most other smuts. Un- state. It generally enters a field on infested wheat seed, fortunately, a bunt common to ryegrass has many of the plant parts, livestock, manure or infested soil carried on same characteristics, which lead to the mistaken conclu- agricultural equipment. While spores can move in the wind, they are relatively heavy and are not believed to be Associate Department Head & ExtensionProgram Leader for Soil and carried long distances. Crop Sciences, Texas Agricultural Extension Service, College Station, Texas A field is first infested with spores (teliospores) brought in cale hay from the regulated area, requiring all harvest and with infested seed, contaminated equipment, etc. These tillage equipment to be subjected to steam cleaning prior teliospores then lie in the soil until conditions become fa- to movement from the regulated area and other restrictions vorable for germination. During a period of cool, wet designed to reduce the possibility of spread of the disease weather, the teliospores near the soil surface can germi- to other locations or into commerce. Wheat that is found nate and produce a new set of airborne spores call pri- to be positive must be heat treated to kill the organism mary sporidia. If this primary sporidia production occurs before it can be used. One effective way to treat such while the wheat is flowering, the fungus can infest the ovary wheat is processing in steam flaking equipment. Other in the wheat flower. If the wheat is not flowering during options available are listed in the regulatory website cited primary sporidia release, these sporidia can produce a sec- below. ond set of airborne spores called secondary sporidia, which give the fungus another opportunity to attack the wheat Best Management Practices flowers. As the kernel matures it becomes blackened with Upon wheat harvest, growers must make plans for the a mass of teliospores and damaged by concurrent bunting coming crop year. If a field is quarantined and the grower or eroding of the embryo end of the kernel. The black still wants to plant a winter grain and/or forage crop, choices teliospores may be internal, covered by the pericarp, or would include oat, barley and cereal rye. If in a regulated loose on the surface of the kernels. Due to the short time area but not a quarantined field, this would leave the op- of wheat bloom and the relatively dry nature of many wheat tions open for wheat and triticale as well as oat, barley and producing areas of the state, it is quite unusual to have even rye. Be especially conscientious about using best man- 1% bunted kernels in any field. The spores on and in in- agement practices in regulated areas. Best management fected mature seed, hay, livestock or agricultural equip- practices to reduce the potential for contamination from ment are quite capable of spreading the infestation to other Karnal bunt would include: fields in which they come in contact. ? Purchase and plant only high quality, conditioned The major cause for concern relative to this disease, com- seed that is inspected or from an area known to be pared to other bunt and smut diseases is marketing. While free of the disease. it poses no danger to the public in food or feed, the U.S. ? Use an effective seed treatment fungicide at planting. and many wheat buying and producing countries either have ? Plant rye, oats or barley rather than wheat or triticale quarantines or severe restrictions in place to prevent move- in infested fields or those in question. ment of infected grain into their countries. The mere suspi- ? Prevent infestation by using only equipment known to cion of the presence of this disease in a very competitive be free of the disease (includes tillage, planting and wheat market is adequate to cancel wheat sales or at mini- harvest equipment). Thorough steam cleaning may be mum significantly reduce wheat price. required to prevent the spread of the disease from in- Current Situation fested fields. In the 2001 infestation, large numbers of positive samples ? Make certain that animals grazing wheat fields have were found in San Saba County. Approximately 42% of not previously been in infected fields or been fed with all samples tested in that county were determined to be infected wheat or triticale grain or hay. infested. In addition, one positive sample was found in a ? Don’t import hay from infected or suspected fields, field on the eastern side of McCulloch County, near the either your own or from elsewhere. western San Saba County border. A new region of infection was also found, with several positive samples being The USDA-APHIS will be screening wheat seed samples found in Throckmorton, Archer, Baylor and Young Coun- planted in the quarantined areas fro the presence of Karnal ties. This new region with several positive samples bunt. APHIS will not screen wheat seed grown outside of prompted the USDA-APHIS to declare the entirety of these the treated areas. Dr. David Marshall’s lab at the Texas counties as “Regulated”. In addition to quarantining the Agricultural Experiment Station at Dallas will be screening fields from which positive identification was made, the regu- wheat seed grown outside of the quarantined areas for the lated status will require that all elevators be tested for pres- presence of Karnal bunt. A $50 fee will be charged for ence of the disease, all wheat harvested be checked for these samples. Samples must be taken by the USDA- presence of the disease before hauling to an elevator or APHIS protocol and submitted to TDA officials for trans- out of the county, a prohibition of hauling of wheat or triti- fer. Detection Efforts and Regulatory Aspects There is a voluntary national survey ongoing at this time to Apart from routine surveys, new pests are often detected help discover the magnitude of the infestation. The Texas when concerned farmers, commodity handlers, Extension Department of Agriculture assists the USDA in collecting Agents, or anyone notices something unusual. If you come grain samples from elevators in the National Karnal Bunt across wheat that you suspect to be infected with Karnal Survey and in other regulatory activities. bunt, or if someone contacts you expressing a similar concern, please acquire a sample of suspect wheat kernels The Federal Karnal bunt quarantine regulations are given and call TDA at (512) 463-5025 for address to send the in the 7 Code of sample for analysis. It is recommended that grain from the Federal Regulations, Part 301.89-1 through 301.89-14 suspect field, or a storage bin should not be moved until and can be accessed at the following website: analysis shows the sample to be negative for Karnal bunt.

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