Q.Plum tree under attack
Can someone please tell me what type of problem or disease is ravaging my plum tree and how to treat it? It has been extremely frustrating the last couple years as it destroys plums that are much better than any store bought plum I’ve ever had. This tree delivers massive 2,000+ crops of plums only to have some 80-90 percent of the plums infected and wasted at the very end when they’re starting to get ripe. I don’t want to cut the tree down but will if I can’t fix this. I’ve attached a photo of the plums. Any help in dealing with this matter would be appreciated. Thank you.

This appears to be brown rot of plum trees. It is a fungal disease. Here is some information on prevention and treatment. https://www.gardeningknowhow.com/edible/fruits/plum/treating-brown-rot-in-plums.htm