flax rust fungus vs flax rust

flax rust fungus and flax rust both are nouns.

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

As nouns, flax rust fungus and flax rust are synonyms defined as:

Other synonyms of flax rust fungus include Melampsora lini.

flax rust fungus (noun)	flax rust (noun)
fungus causing flax rust	fungus causing flax rust