Rhubarb — Food safety facts
Do not feed · Dogs · full breakdown on the linked food page
Leaves contain high levels of oxalates that can cause kidney failure; the stems are also risky in quantity. Keep rhubarb away from pets.
Short answer
Yes. The leaves of rhubarb contain very high levels of oxalates, which can cause kidney failure, and even the stems are risky if a lot is eaten. Signs usually start with drooling, vomiting and weakness within hours. Keep rhubarb plants out of the garden or fence them off, and call a vet if any part is eaten.