Hello,
It look like Black Knot Fungus
I'm not an expert but I know you have to :
1 : Cut the branches and stem that have knot (In winter if possible)
2 : Burn the branches that you have cut for avoiding spreading
3 : Use a fungicide

I already witness black knot be treat like this in the past and it worked but I invite you to inform more about this.

Good Luck with it :)