The disease may have been present in Mexico since 1970 and has been well established in some areas in northwestern Mexico since 1982. Countries with Karnal bunt, on the whole, do not suffer enough loss consistently to initiate eradication procedures. But for the others, it is more economical to let some crops be destroyed than to spend hundreds of thousands of dollars to eliminate the disease, especially since these countries export very little wheat. Although the overall crop losses caused by Karnal bunt might not be severe, the disease has quarantine significance and thus could affect U.S. grain exports. Detection One reason Karnal bunt is difficult to control is that it is difficult to identify.
Infected grain shows none of the symptoms until it has reached maturity.
These diseases are already established in the United States. When checking their crops for Karnal bunt, wheat growers should look for bunted kernels that are fragile, dark in color, and foul smelling. The kernel usually remains whole, although part of the germ may be eroded. Cracks in the surface reveal a black powdery spore mass within the endosperm at the embryo end of the kernel or along the kernel groove. Infection occurs during the flowering stage of the plant, when the developing ovary of a host plant comes into contact with infectious sporidia.