North Carolina Plant Disease and Insect Clinic
Plant Disease Fact Sheets

Pythium stem rot of tobacco - Field

Severe symptoms of Pythium stem rot that remind black shank infection.

Notice the discoloration of the stem due to Pythium stem rot.

Dark discoloration of the stem around the soil line. Typically roots are not infected but only the stem.

Mina Mila


Since 1997, pythium stem rot has been more frequently detected in tobacco cultivars with resistance to race 0 of black shank, especially in fields where cultivars with this resistance have not been used before. This increase in pythium may be due to a reduction in competition from the black shank fungus as a result of resistance.


Symptoms of pythium stem rot are very similar to those caused by black shank, making loss estimates difficult. In most cases, pythium stem rot affects some roots at the soil line level and most of the lower stem, causing a sunken black lesion that will continue to grow upward in the stem. Wilting of plants and a chlorosis are also observed in plants affected by Pythium.

Causal Organism - Pathogen biology

The predominant Pythium species (P. aphanidermatum) has not been detected on tobacco transplants produced in greenhouses in North Carolina; thus the potential of carrying pythium-infected transplants with this pathogen from greenhouses is minimal. However, other Pythium spp. can be carried on infected transplants from the greenhouse and cause seedling blight. Spores of P. aphanidermatum can survive in the soil and plant debris in the field. Pythium aphanidermatum can infect a large number of host plants, including peppers, tomatoes, corn, cucumbers, and peanuts, among others. High temperatures and soil moisture favor the development of pythium stem rot. Most common tobacco cultivars are susceptible to this disease. Other pythium species, including Pythium dissotocum and P. Group Hs, have been detected that cause root rot only.


Because the incidence of this disease depends on environmental conditions, the development of control strategies is very difficult to generalize. Management of this disease may be similar to that for black shank, although resistance to this disease has not been identified.

Other Resources

Tobacco Production Guide:

North Carolina Ag Chem Manual:


Revision date: April 2010