Q.Rhubarb with yellowing leaves
We were given mature rhubarb plants by a friend and told to divide them up into smaller bunches last fall. We planted them immediately and left it alone till this year expecting to be able to get even a few little mature stalks to pick this summer. Well it came up this spring. All the stalks and leaves look healthy at first, but then the leaves start getting brown rust spots, turn yellow and die. The stalks with leaves get to about 18 in. long but are very thin. Are they still usable this year? After the the leaves start to yellow, the stalk becomes weak and starts to die.

Here is an article that will help you.
https://www.gardeningknowhow.com/edible/vegetables/rhubarb/brown-splotches-on-rhubarb.htm