ergot vs plant disease

ergot and plant disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
ergot	Yes	No	No	No
plant disease	Yes	No	No	No

As nouns, plant disease is a hypernym of ergot; that is, plant disease is a word with a broader meaning than ergot:

ergot (noun)	plant disease (noun)
a fungus that infects various cereal plants forming compact black masses of branching filaments that replace many grains of the plant; source of medicinally important alkaloids and of lysergic acid	a disease that affects plants
a plant disease caused by the ergot fungus