I would use a summer or horticultural oil at label rates. Make sure and cover both top and bottom of the leaves thoroughly. Move the plant out of direct sun to a bright shade location for the treatments. Insecticidal soap will also help some but may not kill adult scale as well. It will however help wash off the honeydew and the black sooty mold. You will need to repeat these applications 2 or 3 times at 2 week intervals to ensure more thorough control. Then keep a close eye on the plant and retreat whenever the first signs of scale reappear.
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