Using plants from an infected bed is another way of transferring black root rot, especially where plant beds are planted in or at the edge of fields. Any means of carrying soil from one area to another can spread the disease. However, spread is not as important as letting the fungus build to high levels within the field. There are field sites that are suppressive to the fungus and little disease develops even when the pathogen in introduced experimentally. Dr. David Shew at North Carolina State University continues to study this effect in an effort to understand the situation and use it in control.
Low temperature is a primary factor in the severity of black root rot.
The optimum temperature for its development is an air temperature of 62-74 F, and. This disease becomes most severe only at temperatures unfavorable for the host plant especially cool weather early in the season. The increasing occurrence of black root rot in Kentucky in the past five to 10 years may be partly a result of earlier setting dates into non-rotated sites. It is not definitely known whether soil moisture is an independent factor or if it is simply related to the soil temperature since high soil moisture tends to lower the soil temperature. Excessive rains also stress the tobacco plant because tobacco roots require well-drained soils.