Q.Lemon Tree deceases
Lemons are covered in a walt like skin decease? Can this be prevent, cured. Is the lemon safe to eat?

Certified GKH Gardening Expert
They are edible, and safe. They may not be the best, but they can still be safely eaten. This looks like the beginning of what is called Citrus Brown Rot. This nasty infection will eventually destroy the tree if left untreated.
There are many ways to do so, but the best way is to apply wettqable fulfur and dolomitic lime to the soil. There are many things you can do along with this. This collection of articles will help you: https://www.gardeningknowhow.com/special/organic/