Fruit crop - it varied after onset of autumn (7)
I believe the answer is:
apricot
'fruit' is the definition.
(apricot is a kind of fruit)
'crop it varied after onset of autumn' is the wordplay.
'varied' indicates anagramming the letters.
'after' means one lot of letters go next to another.
'onset of' suggests taking the first letters.
The initial letter of 'autumn' is 'a'.
'crop'+'it'='cropit'
'cropit' with letters rearranged gives 'pricot'.
'pricot' after 'a' is 'APRICOT'.
(Other definitions for apricot that I've seen before include "Juicy stone-fruit related to plum and peach" , "Orange-coloured fruit" , "Small, peach-like fruit" , "Fruit from a tropic" , "I part co with the fruit" .)