wither vs die back

wither and die back both are verbs.

Word	Noun	Adjective	Verb	Adverb
wither	No	No	Yes	No
die back	No	No	Yes	No

As verbs, die back is a hyponym of wither; that is, die back is a word with a more specific, narrower meaning than wither:

Other hyponyms of wither include atrophy, blast, die down, dry up, mummify.

wither (verb)	die back (verb)
wither, as with a loss of moisture	suffer from a disease that kills shoots
lose freshness, vigor, or vitality