Mealy Bugs And Sooty Mold

It looks as though you have an infestation of Mealy Bugs (the white things). The blackened areas are called Black Sooty Mold (or just Sooty Mold). The Sooty Mold is a result of the mold that grows on the honeydew secretions produced by the Mealy Bugs that drops onto the leaves and stems. The Mealy Bugs hurt the plant by sucking out the juices and decreasing the over all vigor of the plant. The Sooty Mold usually does not harm the plant except in severe cases where it prevents the plant from photosynthesizing (we believe your case is severe).
Our suggestion at this point is to try to remove and dispose of all affected plant parts. It is hard to find all the tiny Mealy Bugs so you may want to use an insecticide at that point. We would suggest taking a bagged sample of your plant to your local garden center where they would be able to suggest proper control measures for your particular situation.