No. 3/April 11, 1997
Karnal Bunt Update
Over the past growing season, Illinois, along with other wheat-producing states, cooperated in a survey to determine the extent of a potentially serious wheat disease known as Karnal bunt (KB). Karnal bunt was reported in portions of the Southwest, primarily in Arizona, New Mexico, and Texas. Infestations of KB can result in refusal of acceptance from wheat-importing countries because they quarantine against this pathogen.
Although KB does not cause serious economic loss to the grain, infections result in a fishy smell to grain and products made from KB-infected grain. If only 3% of the grain is infected, this smell can render the grain unusable except for animal-feed purposes. Thus, the USDA initiated a major survey to determine if other areas were also infected.
In Illinois, several agencies (including the Department of Agriculture, Illinois Crop Improvement Association, Cooperative Extension Service, and the Department of Crop Sciences here on campus) cooperated in this survey. We screened over 700 samples from county elevators, farmer fields, trucks, river terminals, and the 1995 and 1996 wheat seed crop. We actually tested over 3,000 seed lots, which were combined in 10-lot increments.
Results: A lot of work for a lot of negatives. But, who's complaining? The Illinois wheat crop was found to be free of Karnal bunt, including some seed lots shipped to other states that had confirmed Karnal bunt in these states and had us retest the seed lots. Still, no positives. So, we are disease-free at this time. I believe that KB will enter the state at some time in the future in one of three ways: on contaminated equipment moved from the Southwest into our area, in out-of-state seed lots from infested areas, or (most likely) by natural infections involving wind-blown spores from an infested area.
KB spores travel very easily in wind currents, and there is no way to stop this from occurring. The real question is, how long until this occurs? If farmers continue to use Illinois-produced seed wheat or seed from areas known to be free of KB, and equipment is not moved from the Southwest into our area, we probably will not have KB for many years. Even if we do confirm it, it does not present the same production limitations that diseases such as scab and Septoria leaf blight do.
A final interesting point: There is a ryegrass bunt whose spores almost exactly match the size and shape of KB spores. This bunt was detected in a number of southern states and caused a quarantine of wheat in those states similar to what happened in the Southwest. However, further lab testing revealed that this was not Karnal bunt but a ryegrass bunt similar in physical appearance. The quarantine has now been lifted, and things are returning to normal.
H. Walker Kirby, Department of Crop Sciences, (217)333-4424