Canker

noun

1. A plant disease marked by gradual decay.
2. A region of dead plant tissue caused by such a disease.
3. A worm or grub that destroys plant buds or leaves; cankerworm.
4. A corroding or sloughing ulcer; especially a spreading gangrenous ulcer or collection of ulcers in or about the mouth.
5. Anything which corrodes, corrupts, or destroys.