white fly again

Lats year my baking apple tree was covered in white fly, covering the ends and joins of branches all over the tree.

I sprayed it last year with a spray in a yellow bottle with bug pics all over it, can you guess I have forgotten the name of it.

I remember reading somewhere that you can spray with soapy water is that for white fly and why have they come back two years running to the same tree, yet they havent touched the pear or plum tree right next to the apple 

Thanks for helping because I know you will have some answers  :happy: