and canker

[Poolfield]

I am doing the winter pruning on my fruit garden and thankfully my cordon apples are looking good but the freestanding apples and pears have a quite bad attack of canker.

I was looking to see how far back I need to cut to remove it but on the Bramley I don’t think there will be much left. Should I just accept defeat and cut it right down and replant with canker resistant varieties?