I have a flowering plum tree and it has started having hard black clumps on it's bark
I have a flowering plum tree that is about 8 years old. I've had no problems with it until the past few weeks as " dark clumps" have started to spread on the outer branches - so many that I don't know if I'll have to have it taken down. I saw this on the same type tree at a friend's house in Silver Spring and it COVERED the entire tree. At that time there were still leaves on my tree with no problem sighted, but her tree was almost leafless. Can I save my tree? Is it a danger to other trees? How should I proceed? Thank you for your help in this. Sorry I haven't figured out how to give you a picture.
This sounds like black knot disease, which is a fungus that causes stem galls. It is fairly common. Here is information and control from our website: http://extension.umd.edu/hgic/black-knot-trees