Weed reduced to powder smells occasionally (9)
I believe the answer is:
groundsel
'weed' is the definition.
(I know that groundsel is a type of weed)
'reduced to powder smells occasionally' is the wordplay.
'reduced to powder' becomes 'ground' (I've seen this before).
'occasionally' means one should take alternating letters.
The alternating letters of 'smells' are 'sel'.
'ground'+'sel'='GROUNDSEL'
(Other definitions for groundsel that I've seen before include "Plant of daisy family" , "plant, unwanted?" , "Common weed" , "feed to the birds" .)