Track to north after day in Wilts (6)
I believe the answer is:
droops
'wilts' is the definition.
('droop' can be a synonym of 'wilt')
'track to north after day' is the wordplay.
'track' becomes 'spoor' (spoor is a kind of track**).
'to north' says the letters should be written in reverse.
'after' is a charade indicator (letters next to each other).
'day' becomes 'd'.
'spoor' reversed gives 'roops'.
'roops' after 'd' is 'DROOPS'.
'in' acts as a link.
(Other definitions for droops that I've seen before include "Hangs loosely or laxly" , "Hangs loosely, sags" , "'Sags, wilts (6)'" , "Grows weak and hangs down" , "Sags through tiredness" .)