Texas A&M Extension specialist Travis Miller says Karnal bunt is relatively new to Southwest wheat producers. It showed up in the spring of 1996 in a sample of durum wheat seed in Arizona.
Subsequent investigation revealed that Karnal bunt had been distributed in durum wheat planting seed and was widespread in Arizona and New Mexico and found in limited regions in California and Texas.
Movement of wheat and wheat equipment was quarantined in Arizona, parts of New Mexico and California, and in El Paso and Hudspeth counties in Texas. A national survey was initiated over the next two years, with samples of wheat being submitted from most of the wheat producing regions of the United States.
The survey found an infestation in San Saba County, Texas, in 1997 in hard red winter wheat, which was the first detection ever in this class of wheat.
Infested fields were quarantined for five years, and a regulated area of a three-mile radius was established around each field, in which all wheat is examined before delivery to an elevator. In quarantined fields, wheat, durum wheat and triticale may not be planted for a period of five years, the estimated longevity of bunt spores in soils.
In the 2001 infestation, large numbers of positive samples were found in San Saba County. Officials determined that approximately 42 percent of all samples tested in that county were infested. In addition, one positive sample was found in a field on the eastern side of McCulloch County, near the western San Saba County border.
A new region of infection was also found, with several positive samples being found in Throckmorton and Young Counties. This new region with several positive samples prompted the USDA-APHIS to declare all of Throckmorton and Young counties as “Regulated.”