My Plummeria along with my Crepe Myrtle and other plants are all of a sudden yellowing and dying. The plummeria leaves are falling off of the tree quickly and the crepe myrtle leaves look like they have a black powdery substance on them. All leaves are discolored, have holes in them, or look like they have some other type of fungus on them. I am unsure of how to treat everything, especially since there is such a large variety in the bed.