I've never grown rhubarb before but I've heard it is very easy to grow. There was a very large overgrown clump at my new house that I divided in February. I didn't harvest any stocks this year to let it recover from the division. The divisions were very healthy but in the last month many of the leaves have started to turn brown and die. I water them regularly and, as the photo shows, some of the leaves look very healthy. I don't see any signs of insects. Is this normal for rhubarb at this time of year, is this some type of disease?
The leaves browning up, at this time of the year, is part of the normal cycle. Just keep watering it during this hot cycle coming up. Thje only insects that bother it seems to ne slugs, as they like the shade, but they do little harm.. and yes you can compost the leaves.
