As a feather in bed is spoilt (8)
I believe the answer is:
'is spoilt' is the definition.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for blighted that I've seen before include "Damaged" , "Spoilt, harmed" , "Spoiled, harmed; infected" , "Withered with disease like potatoes in famine" .)