Answer: There is a good chance that the black substance is mold growing on sap that is leaking from damage caused by aphids. The aphids tend to congregate on the tender new growth tips of the plant and sometimes on the blooms. They are soft bodied sucking insects and can be controlled with insecticidal soap, or a strong spray of water from the hose will knock them down. If you can stop the damage and rinse off the sap, then the mold should also cease.
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