Blue Mold Epidemics in the Southeast first serious epidemic in US was in Carolinas in the 1930s completely wiped out native transplants brought transplants in from out of state, but unfortunately these were infested with another tobacco disease, black shank, caused by Phytophthora parasitica var. In 1979, there was a major epidemic in North America, resulting in 250 million dollars in losses, with 65 million dollars lost in Kentucky. However, presence of oospores is important since it can be a reason to exclude tobacco from export to some countries. Overwintering tobacco has been seen as far north in Kentucky as Owensboro and Louisville during mild winters like 1997-98. Sporulation has not been detected on these plants, however.
Tobacco also is overwintered occasionally in greenhouses further north.
In Texas, wild relatives of tobacco, including Nicotiana rapanda , host the blue mold fungus. All of these can be sources of airborne spores which can be carried to tobacco plants in the spring. Primary source of inoculum is the spore, which is airborne and can be produced in great numbers from the leaves of infected plants. The spores are very sensitive to light and do not survive long unless protected. They can travel great distances in upper air currents.