Collar rot

Collar rot is a symptomatically described disease that is usually caused by any one of various fungal and oomycete plant pathogens.

It is present where the pathogen causes a lesion localized at or about the collet between the stem and the root.

[3] The symptomatically described disease Southern blight is often the first observed precursor of the collar rot caused by the fungus Agroathelia rolfsii.

Causally known as Sclerotial blight,[4] Agroathelia rolfsii survives in the soil as sclerotia, and in infected decomposing plant material as mycelia.

[8][9] Phytophthora species remain in the soil, as spores, and in infected plant tissue, as mycelia, so absent control measures (sterilization, toxic applications) the disease continues so long as susceptible plants are grown in that soil.