Fall in production of plums (5)
I believe the answer is:
slump
'fall in' is the definition.
(slumping is a kind of falling in)
'production of plums' is the wordplay.
'production of' indicates an anagram.
'plums' with letters rearranged gives 'SLUMP'.
(Other definitions for slump that I've seen before include "Sudden market drop" , "Marked decline" , "Sudden decline" , "Commercial decline" , "Fall heavily and limply" .)