whitefly

The easiest and I find successful method is to spray with soapy water . I use a fine spray container .
You can spray as much as you want it only kills the whitefly.
sometimes after 2 or 3 days I will spray with clean water to wash the dead flies off.
I hope this is of some help ? I have been using this method for many years.
IF you have abit of white residue on the leaves it will wash off when you prepare to cook.

I used 1 or 2 drips per litre but it is not that critical I use a 1 gallon sprayer with a pump up handle on the  top.
You can buy these from most garden centres for afew pounds.
It does control them, I know it sounds time consuming but its not really.
The idea behind this method is that it coats the green fly to break down their coating.
Long live fairy liquid.

I've used the yellow sticky card traps and found they do work but if you have an infestation of whitefly you have to  frequently replace the cars as it soon gets coated.