Common bunt is a disease caused by the plant pathogen Tilletia tritici and is common to winter and spring wheat in Canada. These fungi over-winter as spores on the seed surface and in the soil. When infested seeds are sown, smut spores germinate, penetrating the seedling and grow within the cereal host until the heads develop. Smut fungi replace all or most of the grain kernels and form masses of black smut spores instead of seeds and chaff. These spores are released at grain harvest and contaminate the surface of other healthy kernels.
Seed infected with as little as 0.05% bunt balls by weight, produces a pungent fishy smell, as the fungus decomposes the seed tissues. Plants may be stunted and stay green longer. Kernels are totally or partially replaced with bunt balls containing spores of the fungus. Bunt balls are bluish green and turn to grey brown as the plant matures. Common Bunt is particularly evident at maturity, especially shortly after a rain. The fungus can contaminate clean grain and machinery. Spores released from bunt balls at harvest persist in the soil for up to a year. Spores adhering to seed are the most common source of infection. Spores germinate with moisture and infect the seedling through the coleoptile prior to emergence. Low soil temperatures between 5º and 15ºC favor germination and infection of this pathogen.
Bunt is inconspicuous in the standing crop until maturity. Look for moderately stunted plants and those that remain green longer than healthy plants. Check heads on suspect plants for bunt balls. In zones with high incidence or prevalence of this disease, use of seed treatment fungicides is often the best control alternative for the management of the disease.