Breeding ground cultivated to catch disease (6)
I believe the answer is:
hotbed
'breeding ground' is the definition.
(I've seen this before)
'cultivated to catch disease' is the wordplay.
'cultivated' becomes 'hoed' (I've seen this in another clue).
'to catch' indicates putting letters inside.
'disease' becomes 'T.B.' (short for tuberculosis).
'hoed' enclosing 'tb' is 'HOTBED'.
(Other definitions for hotbed that I've seen before include "Breeding ground" , "Scene of rapid growth, as of intrigue" , "Place with ideal conditions for development" , "vicious place" , "Place with ideal conditions for rapid growth" .)