Drc my Helenium is looking pretty much the same as your plants. I'm putting it down to the wet.
I can't offer you any advice though. I was intending to provide a mulch for them but I suspect it will make things worse.
Hope you don't mind me joining in for answers :)

Hi Scottish, I hope that now I have chopped them down and opened them up the air will circulate and help? Lets hope someone has an idea about what we should or should not do?

Do you mean Helianthus rather than Hellenium?
Anyway, once you cut the stems off at or just below ground level, the circulation of air should get rid of any problems like the ones shown.

yes mine is the same. its just the wet and i have cut out the dead stems and this has worked in the past. so nothing to worry about Drc.

Thank you Owdboggy and SBG, I'm sure Drc will be as pleased as I am that it's nothing to worry about.

Yes I did mean Helianthus Lemon Queen Ob. Thanks everyone as I would hate to lose them.

If you are worried about the Helianthus, then pull off a root section from the outside of the plant and pot it up and keep it somewhere safe over winter.

Thanks OB, might do that.

I have just done this with H. giganteus Sheila's Sunshine. It had fallen over and pulled itself out of the ground. Don't particularly want any more of it, but what the heck, I can always give it away.

Ha ha.

Cut back, add dry straw, cover with fleece, cover in plastic. OR Rhubarb pot, keep out the wet.