Hi Vivien and Johnboy
Yes I had considered cane spot but have never seen the purple spots. A quick google for supercarb suggests everybody recommends but nobody sells!
Had not thought about vine weevil and will check but wouldn't the dead canes snap off easily if this was the cause?

Over the past few years a 25ft row of raspberry canes (Glen Ample) has died....new canes grow well until the fruit starts to turn colour and then the cane shrivels and dies. Large gaps are left in the row and now there is almost nothing left. What has caused this and should I be worried for my Autum...