jennifer.. I know nothing about rhubarb but isn't it a perennial plant. Since it has become infested by ants, I feel what I might do would be to dig the entire plant, put it into a tub of water to rehydrate for a few hours and to disengage the ants. I would probably stand by with an aersol can of ant spray to spray the ants as they crawled out with a direct hit. Then, I would do everything possible to remove them from the earth, either with the spray on the surface, boiling water into the hole, or by using bone meal. We have had success pouring bone meal directly into ant hills but have never dealt with a similar challenge. I would prepare a non infested area to replant the rhubarb and keep a check on the original site to continue eliminating the ants. Most perennial plants will recover in time as long as the roots are not severely damaged or dehydrated. Hope this helps. EP