Answer: Comfrey is one of the most difficult perennials to eradicate because of its deep root system. While you might be able to spot treat with an herbicide such as Round Up, you run the risk of accidentally touching your other plants with the spray. You could pull the tops of the comfrey plants and then paint Round Up on the stump. That should be reasonably safe for your other plants. An additional step would be to cover the stump with several thicknesses of newspaper or even black plastic. Without sunlight, the comfrey will eventually die out. You might try both techniques.
Best wishes with your project!
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