Answer: Sevin is an insecticide, not a fungicide so I don't think it would do anything for the black on the stems. And, Sevin kills all insects, including the bees that might visit your flowers and transfer pollen so the flowers will turn into fruits. So you may have chased them all away with your Sevin applications. I don't know what the black substance might be. If the leaves look healthy and your plant is producing flowers, I think you will eventually get fruits. Just be patient with your plant. Best wishes with your topsy turvey planter!
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