Raspberry plants leaves shrivelling, going brown and dying...

Hi all

I had a problem with a couple of canes two months ago whereby the leaves were starting to yellow. The rest of the plants in the long row seemed unaffected, so I pulled the bad one up and didn't overly worry about it. I posted a thread at the time which is here:

http://www.gardenersworld.com/forum/fruit-and-veg/raspberry-plant-problem---yellowing-wilting-leaves--any-ideas/999991.html

I thought it best to start a new thread today as the problem I'm now having might be something different. But I mention the previous one in case they are related. The problem now can be seen in the photos below. A couple of canes are affected. One is a new cane (green) and the other an old one (brown). Both have the same shrivelled brown leaves. The last photo shows the top of the affected green cane, which hasn't browned/shrivelled yet but isn't looking too happy and I suspect will soon follow. 

Does anyone have any ideas what the problem might be and what can be done?

Many thanks 

Max