The sun is responsible for this scourge for farmers starting off (5)
I believe the answer is:
light
'the sun' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for light that I've seen before include "Mild" , "Illuminate or ignite" , "Pale" , "free gift from The Sun" , "Delicate; illuminate" .)