I have a wonderful poinsettia plant that I have been taking care of for more than 2 years now. Less than 3 weeks ago, I noticed brown spots all over about half of the branches, particularly the smaller branches. At first I thought it was a disease. The brown spots rubbed off easily and figured that it must have been dried sap. The plant was fine for about a week and then the leaves started yellow and entire branches were dying. Currently, only 3 large branches appear to be un-affected, but I know that it's only a matter of time before they start dying back. What is happening and is there a way I can save my poinsettia?