Karnal Bunt Disease

What is Karnal Bunt Disease?        

Karnal bunt is a fungal disease of wheat, durum wheat and triticale. Typically, only a portion of the kernel is affected, leaving an eroded or "bunted" area on the kernel and a mass of black spores which produce an offensive "fishy" odor.  Some other smut and bunt fungi attacking wheat can produce similar fishy odor too.

Karnal bunt spreads by spores through the movement of infected wheat seed, plants or straw or even through soil carried on agricultural equipment. Spores can even be carried on the wind, although they are relatively heavy and are not believed to be carried long distances.

Spores can live in the soil five years or more until conditions favor growth, usually a period of cool, wet weather. A fungal mat grows on the surface of the soil, and this growth sheds secondary spores. If these spores are released during the flowering stage of wheat and come in contact with the wheat ovary, bunted kernels are produced.

Look for grain that has partially eroded or bunted kernels. Karnal bunt infected grain will have an offensive "fishy" odor.

If you suspect a shipment of wheat has Karnal bunt, contact TDA at (512) 463-5025. They will will arrange for samples to be taken and provide guidance for analysis.

Picture of wheat with Karnal Bunt


If a Karnal bunt-positive shipment of grain has been in your storage facility, then all conveyances, equipment and structures used for storing the grain must be cleaned and disinfected in the presence of a USDA or TDA inspector. First remove all soil and plant debris and then disinfect by one of the following methods:

  • Apply steam at the critical temperature of 170 degrees F to all surfaces to the point of runoff.

  • Clean with a solution of hot water (180 degrees F minimum) and detergent applied under pressure of at least 30 pounds per square inch.

  • Wet all surfaces to the point of runoff with a solution of 1.5 percent sodium hypochlorite and let stand for 15 minutes. Thoroughly wash down after 15 minutes to minimize corrosion.

  • Fumigate with methyl bromide at 15 pounds per 1,000 cubic feet for 96 hours.

While wheat with Karnal bunt is not harmful to humans or livestock, it cannot be sold as grain and must be heat-treated and used for livestock feed or for flour. However, flour made from bunted kernels is discolored and has an unpleasant, though harmless, odor and taste. Generally, wheat containing more than 3 percent bunted kernels is considered unfit for human consumption.

The major impact of Karnal bunt is to our export market since many countries will not allow imports of Karnal bunt-positive wheat, virtually closing some markets. The United States is the world's leading wheat exporter, accounting for 25 to 30 percent of world wheat exports. In 1999, Texas ranked fifth in the nation in wheat exports with a total of $209.1 million.

If Karnal bunt is found in a field, USDA will place the entire county or a portion of the county under quarantine which restricts the movement of regulated items such as wheat grain, plants, seed and straw; soil; equipment including trucks and railroad cars used to move wheat; and farm implements and equipment used in planting, harvesting and wheat processing. The quarantine also covers cleaning of storage facilities.