They may be suffering from root problems due to soggy wet or dry soil, or from soil pH levels that are too high. I suggest you start weekly fertilizing with Miracid which is a soluble fertilizer at the label rate. This should improve leaf color and plant vigor. The black mold is probably from whiteflies or scale. Your County Extension Office can suggest some control products for these pests but may want to see a sample from the plant in order to make a good diagnosis. Place a section of branch into a clear plastic bag to keep any insects in the bag until the Extension Agent can see the sample.
Thanks for the question. Please stop in again soon!
Q&A Library Searching Tips