Pathogen(s) causing disease:  Tilletia indica (also known as Neovossia indica)
Symptoms:
The disease cannot be easily detected in plants growing in the field: the grain must be removed from the head and examined. When checking crops for Karnal bunt, wheat growers should look for bunted kernels that are fragile, dark in color, and fishy 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.
Conditions:
Karnal bunt is spread mainly by the planting of infected seeds. Infection occurs during the flowering stage of the host plant, when its developing ovary comes into contact with infectious sporidia, a stage in the lifecycle of the pathogen Tilletia indica. The ideal conditions for infection are cool weather, rainfall, and high humidity at the time of heading of wheat. Spores can be carried in soil and on a variety of surfaces, including seed and other plant parts, farm equipment, tools, and even vehicles. They can also be windborne. KB spores are uplifted during the burning of wheat fields, and areas downwind may become contaminated if the spores remain viable.Â
The ideal conditions for infection are cool weather (59 to 72 F) and rainfall, overhead irrigation, or high humidity. The weather during heading and for a few weeks afterward is critical for disease development. If there is no cool, rainy weather, KB will be negligible.Â
Spores can survive in soil for several years under certain conditions. Moderate temperatures and dry soil during fallow periods, such as occur in the southwestern states, favor survival.
Management: None available
Sources:
USDA http://www.aphis.usda.gov/publications/plant_health/content/printable_version/fs_phkarnal.pdf
University of Idaho  http://www.uiweb.uidaho.edu/ag/plantdisease/kbwheat.htm
