I would try Bt (Bacillus thuringiensis) from the garden supply store. It's a non-toxic (except to caterpillars) powder that won't affect bees, earthworms, etc.

Sue

Yes, Bt will work well, as will a spray of rotenone and pyrethrins to knock down any live acitivity quickly. Usually there are not many pests for rhubarb and its fairly hardy on its own. If yours is spindly, a good rich fertilizer is helpful too. If the chewing is larger like whole stems almost chewed through, it could be rabbits or a rodent damage.

Do you mean the leaves are chewed or the stalks?

Chewed leaves will not harm the quality of the stalks.

Usually only slugs will chew the stalks, leaving pits or
elongated shallow trenches. Just pare theses spots out when preparing the stalks for cooking.