Certified GKH Gardening Expert
It is likely that the tree is suffering from a bacterial issue. I have a remedy that I use, personally to control a broad range if fungus, bacteria, and insects. If it alright if you don't have every ingredient, but it works best if you do. Please don't neglect the soil priming.
Here is the method: First, you will want to prime the ground with dolomitic lime, then spread wettable sulfur to Kill off any infection in the soil. I Also like to spray the plant itself. Mix a few drops of one or more of these ingredients into warm water with a spoonful of coconut oil: Rosemary oil, lavender oil, neem oil, garlic oil, cinnamon extract/oil and for really bad cases, also add clove oil.