I have flowering plum trees that are losing their leaves. They also have little holes in the leaf with black around the holes. The branch is also dead.
Flowering Plum Tree
Certified GKH Gardening Expert
This could be the onset of a fungal issue or insect pests. I would recommend treating the tree with neem oil, which will take care of both problems. Here is more information: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm