An internet search yields info on 'rhubarb red leaf disease'. Google that for images and a few look similar.
<<the plant probably is infected with bacteria called Erwinia rhapontici. This is one of two conditions called red leaf, and in this case, the name is well earned. The entire leaf begins to turn red and the crown and the roots of the plant end up rotting. While seeing frilly red leaves might look pretty at first, it is a sign that the plant is severely infected. The only treatment for rhubarb infected with Erwinia is removal and destruction. You will not be able to plant rhubarb in the same spot again, and you will need to control insects in the area to avoid spreading the bacteria to other rhubarb plants.>>