This pest in nursery could get fired (4)
I believe the answer is:
slug
I believe this clue is a double definition.
'this pest in nursery' is the first definition.
(a pest in a plant nursery)
'could get fired' is the second definition.
(slug can mean a bullet)
(Other definitions for slug that I've seen before include "gulp!" , "Bullet - punch" , "Bullet -- shot of liquor" , "Terrestrial mollusc" , "draught" .)