does this help Yorks.
https://www.rhubarb-central.com/rhubarb-diseases.html

Thank you Eileen. I've just been to have another look and its worse than I thought. I couldn't see anything on the website that matched it, unless it has been short of water during the long dry April. But then the whole plant would have been affected I would have thought. What's left still looks healthy so fingers crossed. I don't know what to do short of watering it some more. I've taken off all the affected leaves for starters.

I have been toying with moving it to a different site for a while so if I lose the lot it will spur me on to start again with new plants - but that means a whole year without a crop which doesn't bear thinking about!!!

Can you add a photo?

Too late, I took all the affected leaves off this evening. if any more are affected I'll try to get a shot then.