Nip in the bud
Put a stop to something while it is still in its early development.
This phrase derives from the de-budding of plants. The earlier form of the phrase was 'nip in the bloom' and this is cited in Henry Chettle's romance Piers Plainnes Seaven Yeres Prentiship, 1595:
"Extinguish these fond loues with minds labour, and nip thy affections in the bloome, that they may neuer bee of power to budde."
A version of the current 'bud' version of the phrase first appears in 1607, in Beaumont and Fletcher's comedy of manners Woman Hater (a title that they would probably have difficulty convincing a publishing house to use today):
"Yet I can frowne and nip a passion Euen in the bud."