Certified GKH Gardening Expert
I see one photo of what appears to be a bacterial infection. I would also check the pH of the soil in that area.
You can get it, roughly, neutral and can kill off the infection with an easy solution: Dolomitic lime and wettable sulfur will do just this. It will kill the infection, as well as stabilize the pH to something very close to neutral so that you can work from there.