Infested transplants are a major means of long distance spread as they often harbor the disease without symptoms present. The higher the pathogen population at the start of the season, the greater is the potential for serious crop loss. Black shank can be an explosive disease that appears suddenly if the right weather patterns develop following introduction of the pathogen into a field, even where just a small amount of the pathogen was introduced into the planting. Great spread can occurs from a small amount of initial pathogen, with the spread following patterns of water movement and cultivation. The potential for black shank in infested fields is very dependent on environmental conditions that impact fungus reproduction and susceptibility of the plant.
Water is critical to reproduction of the fungus and infection of the tobacco plant.
Multiple generations occur in the same season, greatly increasing the amount of pathogen available for late season epidemics and for survival. Once this fungus is on the farm, it has the potential to cause great damage year after year. The fungus reproduces on all tobacco varieties, including resistant and susceptible varieties. Overall plant health greatly impacts the severity of black shank in resistant varieties, with stressed plants much more likely to sustain serious loss. Often plants with black shank do not turn yellow or die until the plants are stress by conditions such as drought or topping.