Main Symptoms
 

Oomycetes, especially Pythium spp., may cause brown, moist and soft lesions on the stem of the plants.  Lesions are found at the soil line. Sometimes, the roots are affected. They turn light brown and their cortex eventually disintegrates.

Infection may also occur after planting. Typically disease occurs in fields during periods of favorable (wet) weather conditions and in the presence of particularly aggressive strains.

Symptoms include browning and death of many feeder roots and decay of the root cortex, the taproot and the buried portion of the stem. The presence of oospores can be observed in infected tissues with a microscope.

Foliar lesions may also be observed on the lower leaves. They result from splashing of contaminated mud during rainfall or long irrigations.

Some of the information on the disease distribution worldwide is obtained from surveys conducted by CORESTA (Cooperation Centre for Scientific Research Relative to Tobacco). The reliability of the information is not confirmed in all countries.