Rose Canker. Please help identify the problem

I believe my knock out roses have canker really bad. They are all still starting to grow this spring but the canes almost look like zebra stripes all the way down to the base. I'm not sure how to proceed or if they can be saved? I'm new to roses and these are 3 years old. I'm sure the problem began way before I realized what it was. I've been properly reading on care as of recently. I just assumed knockout roses were an easy plant as everyone in the area seems to have an abundance of them in their landscaping. Zone 6b. The light tan stuff is fertilizer I was working into the soil just as an FYI and not rot.