Raspberry Advice Wanted

Long time reader, first time poster!

Last year, my other half and I took on an allotment in the Speedwell area of Bristol. Among the various fruits we planted were half a dozen bare canes of Polka raspberries. These came up very well last year and gave us a great crop of raspberries up until early December when the weather finally became to cold!

At the end of January we cut all the canes down to ground level (well maybe an inch above ground level) with the exception of two plants were we left one cane each which had grown but hadn't produced fruit the previous season in an effort to double crop and obtain some early fruit. This season 5 of our plants have come up well and our attempt to double crop has worked well on one of the plants. Unfortunately the other we tried to double crop is looking a bit sickly. From March to May, the cane we didn't cut on this plant started to bud, develop flowers and then fruit. In the same time period 3 new canes grew up from the ground though the canes themselves developed very few leaves and were effectively bare. The leaves on the cane we didn't cut back then started to turn yellow and then brown whilst the fruit stopped growing and appeared very dry. As the fruit bearing cane appeared to be dying I decided to cut it down to ground level a few weeks ago. This left the 3 canes which grew this year though the canes had very few leaves. Since then leaves have started to grow though near the top of one of the canes is a black/purple mark, there also appears to be one at the bottom of one of the canes as well (see pictures). Is this raspberry cane spot or spur blight? Should I dig out the plant and its roots and burn them? Any advice would be most welcome!

 

I haven't come across this problem before but it does favour the Spur blight sadly .