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.
Stressed plants are easier prey for the black root rot fungus.
Failure to rotate tobacco land is the most important factor in the disease's build-up and persistence. Soil pH has been found to influence the incidence of black root rot. Using lime on tobacco fields makes conditions more favorable for the development of black root rot, but tobacco grows poorly without proper liming. Apparently, it is not pH effect alone, since the optimum pH range of the fungus in culture is 4.0 to 6.4. Research conducted at North Carolina State University indicates that under low pH conditions toxic elements such as Aluminum are release which slows the development of the black root rot pathogen and or kills it.