This plant has grown in same spot in a closed in garden open to sky getting light but little sun. Hasn't bloomed much but this year not at all. The leaves are dropping some, and the remaining leaves are covered with a sooty black substance. Could it be the aftermath of an ant and aphid infestation? I did not see insects but I don't look at this plant much in the winter. It is now a small tree due to my pruning practices and the limited space, with the top branches above the surrounding walls. I will try water pressure but I need advice. Thank you.