Collar rot

Collar rot is a symptomatically described plant disease usually caused by one of various fungal or oomycete pathogens, producing a lesion localized at the collet between stem and root that develops into a girdling collar. It observationally grades into basal stem rot, sometimes followed by root rot, and is most often seen in seedlings grown in infected soil. Its causal pathogens may be species or genus specific, though generalists such as Agroathelia rolfsii are known to attack more than 200 different plant species; bacterial collar rot is uncommon, though trees infected with fire blight may develop it, and non-parasitic collar rot can also result from winter damage. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/