Appear to have harvest increased (4,2)
I believe the answer is:
crop up
'appear' is the definition.
(I know that crop up has the is a more specific form of the action appear)
'harvest increased' is the wordplay.
'harvest' becomes 'crop' (synonyms).
'increased' becomes 'up' (something that's up has increased or risen).
'crop'+'up'='CROP UP'
'to have' is the link.
(Other definitions for crop up that I've seen before include "Occur, arise" , "Occur unexpectedly - as part of harvest?" , "Occur by chance - like harvest?" , "Occur unexpectedly - like harvest?" , "Appear unexpectedly" .)