I live in Saskatchewan, Canada to start with. My 2 year old rhubarb gave me at least 3 or 4 healthy crop yields so far until just now some leaves are starting to turn yellow rapidly and I wondered why. Having grown and eaten rhubarb stalks for the last 40 or 50 years, I see the new abnormalities with rhubarb in my rain barrel filled with top soil and being water fed from rain spout from roof top entirely covered with tar shingles. Tar issue the problem I wonder? Or chemicals from metallic (aluminum) downspouts? Thank you in advance, Ron
Rhubarb Leaf Turning Yellow, Why?
Certified GKH Gardening Expert
I'm suspicious of the watering you mention.
The leaf does not really appear as a leaf spot disease, but more clearly matches the description in the last paragraph of the article below.
I have not been able to locate an image that matches your leaf coloration.
I would move the container and water with a different source of water. You may even want to flush the soil with fresh water.