DISEASE CONTROL

Detection of Wheat Disease in Arizona Impacting North Dakota
Growers
 
On March 8, 1996, the US Agricultural Research Service and the
Animal/Plant Health Inspection Service confirmed the presence of
a wheat disease, KARNAL BUNT, in some durum fields (var. Reva) in
Arizona. The USA had been considered free of this disease, with
known infestations reported only in parts of Mexico, India,
Pakistan and Iraq. Twenty-one countries are known to regulate or
prohibit grain movement on the basis of Karnal bunt. The presence
of this disease in Arizona now means the US can no longer be
considered free of this disease. The immediate area affected in
Arizona is under an emergency quarantine, but until further
evaluation of the problem, phytosanitary certificates for
shipments of wheat from the US to countries with Karnal bunt
restrictions will not be issued. A panel of experts is now
meeting in Arizona to review the existing Karnal bunt action
plan. Karnal bunt is NOT present in wheat in North Dakota or
neighboring states. Yearly field surveys, plus seed washing
surveys to detect Karnal bunt were done in 1995 from Texas
northward through North Dakota. Karnal bunt was not found! This
large wheat-producing zone is free of Karnal bunt. 
 
Description of Karnal Bunt Wheat Disease
 
Karnal bunt is caused by a fungus, Tilletia indica. The fungus is
introduced into a new area by movement of the spores on seed
(hence the import restrictions). The spores are introduced into
the soil. The fungus then develops from these spores at or near
the soil surface, is carried to wheat heads by wind, and infects
the flowers and developing kernels, eventually causing cracked
kernels partially replaced with the black bunt spores. Both yield
and market quality of the grain are affected. Bunt spores are not
a health risk to livestock or humans.
 
It is not known if the spores of the fungus would survive in the
cold soils of northern climates. Currently, this disease is found
only in tropical or very warm climatic zones. Also, little
information is available on how much damage this disease does to
production in areas where it occurs. The Karnal bunt fungus is
not easily controlled with seed treatments or other chemical
treatments. Currently, the biggest impact Karnal bunt poses to
North Dakota producers is its potential to affect export markets. 

(Submitted by Marcia McMullen, Extension Plant Pathologist)