After warning, throw out parasitic plant (9)

'parasitic plant' is the definition.
(toothwort is a type of parasitic plant)

'after warning throw out' is the wordplay.
'after' is a charade indicator (letters next to each other).
'warning' becomes 'toot' (sound of a car horn).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'throw' with letters rearranged gives 'hwort'.
'toot' next to 'hwort' is 'TOOTHWORT'.