whiteflies on Italian parsley

Every year for the past few years the Italian parsley in a container on my deck gets infested with whiteflies. It's already happened this year... before the end of June.

I would appreciate any advice on stopping this cycle. Should I pull out the plant and replace it...with or without replacing the soil? Could I pull out the plant, seal the dirty roots in a plastic bag and dunk the plant in soapy water for a few minutes then rinse and replant?

 

Have you tried insecticidal soap?

 

I'm reluctant to use it on something I'll eat.

 

Insecticidal soap is allowed on organically certified produce.