Do the 'white puffy things' resemble cotton wool? If so, sounds like mealy bug, which is a pest that draws the sap from leaves causing them to yellow and eventually die off. I can't remember what the precise remedy is for mealy bug off the top of my head. I know that you are meant to physically scrape them off the plant then apply some kind of pesticide, but can't remember which. As mealy bug have hard waxy outer shells, many pesticides cannot penetrate them so only a certain kind are suitable. No doubt if you think it could be mealy bug and you do a web search, you'll find help or ask for advice at your local garden centre.