Assemble to conclude harvest (6)
I believe the answer is:
gather
I believe this is a triple definition!
'assemble' is the first definition.
('gather' can be a synonym of 'assemble')
'to conclude' is the second definition.
(gathering is a kind of concluding)
'harvest' is the third definition.
(I've seen this before)
(Other definitions for gather that I've seen before include "Come together for the rag" , "Collect or assemble" , "Accumulate, garner" , "Collect together in one place" , "Accumulate, amass" .)