Answer: Scales have a hard, protective coating that is impermeable to sprays. The insects need to be dislodged to be killed. Try scrubbing the scale off with a toothbrush dipped in rubbing alcohol. Rinse the leaves afterward to avoid any burning from the alcohol. You can also use insecticidal soap to kill the "crawlers", the tiny mobile, immature scale that are vulnerable before they secrete the hard covering. Keep the plant out of the sun for a couple of days after any treatment. Good luck!
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