Please help me identify the disease on my plum tree fruit seen on the attached pictures. Thank you very much!
The disease on the branch or trunk (hopefully not) is almost certainly Black Knot, a fungus disease that can only be cured by removing the infected area and all tissue within 4 inches of it. It is very common on plum trees (I just removed an infected branch on my plum tree today). The disease on the fruit looks like brown rot, but it's hard to tell from the photo. Various sprays can control brown rot, although I've never found it to be a problem on my plums.
Thank you about the black rot. I posted another picture of the plum. There is a gooey substance on the surface and black patches inside the fruit.
That doesn't look like brown rot, but I've never experienced anything similar; so I'm afraid I can't help with the fruit disease.
