my rhubarb has yellow leaves which are drying up

Question

these rhubarb plants were planted here 3 years ago

Answer 1

Yellowing and wilting of the leaves could simply be lack of water at crucial times - the broad leaves need copious amounts of moisture in summer. Or it could be a fungal disease. Check the crown of the plant at the base of the leaves close to soil level for white fungal growth or rot
https://www.gardeningknowhow.com/edible/vegetables/rhubarb/grow-rhubarb.htm