I have purchased two mediterranean fan palm for outside my front door in big tubs butI have noticed that they have white like powdery fluff all over the leaves is this normal or does it have a bug ?
That sounds like a description of mealybugs. You might get a magnifying glass and look closely as you poke them a bit to see if they move. If so you can treat them with either a lightweight horticultural oil or a stronger insecticide. Repeat treatments are usually needed as you usually don't get everything with the first try.
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