Insecticide desperate man put down in row (7)
I believe the answer is:
lindane
'insecticide' is the definition.
(lindane is a kind of insecticide)
'desperate man put down in row' is the wordplay.
'desperate man put' becomes 'nda' (I can't justify this - if you can you should give a lot more credence to this answer).
'down in' is an insertion indicator.
'row' becomes 'line' (as in a row of things).
'nda' put into 'line' is 'LINDANE'.
Can you help me to learn more?
(Other definitions for lindane that I've seen before include "killer" , "Synthetic insecticide" .)