I need Idiomatic expressions

[Unregistered]

Dear Teacher ,
could you please help me to find an idiomatic expressions for the following sentences:
1.A single flaw which spoils the whole
2.Destroy at the very start

[Dandelion]

1. One rotten apple spoils the whole barrel.
2. Nip in the bud (stop something that is in an early stage of development)

[Tomasz Klimkiewicz]

Dear Teacher ,
could you please help me to find an idiomatic expressions for the following sentences:
1.A single flaw which spoils the whole
2.Destroy at the very start

2. to kill in germ

[Dandelion]

2. to kill in THE germ