One of the inevitable things about growing plants is that at some point you will be faced with some unwelcome guests that want to share your production. It is very important to realize that the choices that are made for dealing with those visitors can have a direct effect on the food you consume. Many pesticides are registered for use on leafy greens in Canada the US and Mexico. Some of those chemicals are actually systemic ie. they are taken up by the plant and translocated through its tissue. The use of those pesticides will always have unintended consequences and that is why is is best to err on the cautionary side. In some cases pesticides certified for organic use and not a good choice either and can have unintended effects on both people and the environment.
In our case we try to use a combination of biological pest control that succeeds by reaching an equilibrium with the respective pests that is being controlled.
These are our most consistent problem. In order to control aphids we have to use a multi-faceted approach using a series of predators and parasites and in extreme cases spraying with insecticidal soap. The parasites we use are Aphidius colemani and Aphidius ervi. The predators we use are Aphidoletes aphidimyza, Hippodamia convergens (Ladybugs) and Hoverflies.
A big problem with spraying even something as innocuous as insecticidal soap is that it may kill the beneficials population as well which may end up putting you in a worse position in the long run.
A far less common problem then aphids but if populations build up can cause a lot of damage. We use a parasistic wasp called Trichogramma pretiosum.