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. Infection occurs after heading when sporidia produced from spores germinating at the soil surface are dispersed to the glumes of the wheat spike. 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.
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. Even though previous research might suggest conditions in temperate climates are not favorable for spore survival or disease establishment, the introduction of contaminated seed may lead to minor outbreaks during subsequent years. Thus, we need to be extremely vigilant regarding seed sources. Chemical seed treatments used to control other bunt and smut diseases of wheat are not effective for control of KB, because there is insufficient chemical in the plant at heading when infection occurs. Fungicide seed treatments have been used to reduce the spread of inoculum via seed.