wheat rust vs rust fungus

wheat rust and rust fungus both are nouns.

Word	Noun	Adjective	Verb	Adverb
wheat rust	Yes	No	No	No
rust fungus	Yes	No	No	No

As nouns, rust fungus is a hypernym of wheat rust; that is, rust fungus is a word with a broader meaning than wheat rust:

Other hypernyms of wheat rust include rust.

wheat rust (noun)	rust fungus (noun)
rust fungus that attacks wheat	any of various fungi causing rust disease in plants