Definition of neck rot in US English:

neck rot

noun

Botany
  • Any of several diseases affecting the necks of bulbs or plants; especially a disease of onions caused by the fungus Botrytis allii, characterized by blackening and decay of the top of the affected bulbs.

Origin

Early 20th century; earliest use found in Liberty Bailey (1858–1954), horticulturist and botanist.