Pygmy Palm Is Covered With White Spots

Question: We have a triple trunk Robellini Palm in our screened in pool area in Orlando. It has been beautiful for years. In the last few months (noticed mid July) the fronds have lots of small white spots, then get covered in what looks like black ash or soot and eventually die. The trunk area is becoming black and even the stones outlining the area. We have tried volck oil spray four times a few weeks apart. I cut off the worse leaves, mostly at the bottom but now the new growth at the top has the little white spots appearing. Please offer advice on what to apply. Thank you.

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