It’s possible the white powder on your Kalanchoe luciae “Paddle Plant” (or Flapjack) is actually normal, but it could definitely be powdery mildew too. The paddle plant naturally produces a powdery white coating that helps keep it healthy. You can see it in the picture here.
If this is what you’re seeing you don’t have anything to worry about. However, if what you are seeing begins to cause discoloration, deformed leaves, and other less than ideal symptoms, it likely is mildew and should be treated.
Mildew likes a warm, wet environment, with little air circulation. If your Kalanchoe is indoors, consider moving it to an area that gets better air circulation. Be sure that when you are watering, the leaves aren’t getting wet, and the soil is drying out completely between waterings.
Remove any leaves that have become infected. Some people have found that milk diluted with water and applied to the plant has been effective, as well as baking soda mixed with dish soap and water. Be careful when applying baking soda to your succulents, as repeated exposure can burn leaves.
Until the mildew is contained, it’s best to keep it separate from your other plants and succulents.