I bought some roses from Home depot about three weeks ago. They are canes with a few leaves. After I planted them in my garden, they growed very well. There was a couple days code weather (around 30 F at night) here in NC. I didn't do any protection. I found some canes turned to black and leaves on those canes dropped. Some other canes are doing well. Should I cut the black canes? Is this caused by the cold weather or some type of diseases? Thanks for your attention.