For what its worth I keep a tub of clean water with a lid on at the lotty..
I dunk all my greens in this, giving em a shake afterwards
You will see the white fly floating on the top of the water after doing this. I keep one of those car washing brushes there too, its got fairly soft bristles. If I see produce with the white stuff the whitefly leave.(Kale seems to get affected quite bad on the backside of the leaves.) I give it a good scrub under the water during dunking ..This method is also used on most root crops too .
Saves me getting my ear chewed for whitefly buzzing around the kitchen or soil and mud on the worktop or draining board. ;)
WARNING to other guys on lotties. Don't expect to do this on nice days, then come a bad cold icy day you dont fancy dipping the stuff in the tub.Because once you start taking home clean carrots ,leeks ,Parsnips etc .Not doing it cos its cold won't be tolerated by her indoors.. :D Also saying it looks more "organic dear" don't work ..Well didn't for me