No reason to consume starter of niffy rhubarb (8)
I believe the answer is:
nonsense
'rhubarb' is the definition.
(I've seen this before)
'no reason to consume starter of niffy' is the wordplay.
'reason' becomes 'sense' (I've seen this in another clue).
'to consume' indicates putting letters inside.
'starter of' says to take the initial letters.
The first letter of 'niffy' is 'n'.
'no'+'sense'='nosense'
'nosense' going around 'n' is 'NONSENSE'.
(Other definitions for nonsense that I've seen before include "Gobbledegook" , "folly" , "Words or ideas that don't make sense" , "Language without meaning" , "Foolish or meaningless words" .)