Gunnera Manicata..Leaves browning.

I asked this last year without solving the problem.My Manicata has grown very well again this year and next year will be resited for more space.
However...half of the huge leaves have once again started to go brown.Some on the outer edge of the plant and others in the middle. No it's not the sun scorching water on the leaves...or lack of water (The site is extremely damp partly shaded by silver birch) The ground was well manured with chicken manure before the spring,and regularly since.
I've seen this problem asked on Google...but never seen an answer.Has anyone had this problem with theirs?







Some leaves are unaffected...

 

It may be a long shot but I have had similar on Rhubarb Leaves not in this garden but in another house I lived at , so it may be Leaf Spots - Ramularia and Ascochyta (Fungi).

Picking off the leaves helps and after it has died down if you can remove the top couple of inches of soil compost and replace with fresh in the spring before the leaves start to shoot may help

Spruce