Pests

Over the mild and wet winter here in Somerset, my greenhouse has become invaded by whitefly.  Today, I have had to clear my raised veg bed from claytonia and winter salad leaves which would have been perfectly edible had it not been for the whiteflies all over them.  Last Autumn we had pressure washed inside the greenhouse, and it was completely clean and clear, so I can only put this down to the mild conditions.   Should I remove and replace the topsoil and compost in my 2 veg beds to completely eradicate the whitefly before sowing new crops?  I garden organically, so I did not want to use chemicals.