Plague in soldier's home country, not unknown (6)
I believe the answer is:
blight
'plague' is the definition.
(I've seen this before)
'soldier's home country not unknown' is the wordplay.
'soldier's home country' becomes 'blighty' (WW2-era informal name for Britain).
'not' is a deletion indicator.
'unknown' becomes 'y' (algebra).
'blighty' with 'y' taken out is 'BLIGHT'.
'in' acts as a link.
(Other definitions for blight that I've seen before include "Fungal disease - destructive force" , "Plant disease or malign influence" , "Plant disease -- calamity" , "Withering disease (in plants)" , "Disease - pest" .)