I have found that tropicals are very sensitive to flouride usually found in tap water...it will do the Cordylines in really fast. But it will flash off with the chlorine if left in an open container.
I would caution using mayo or oil to wipe the leaves of plants. Plants 'breathe' and receive all kinds of signals thru their cellular structure in the leaves (stomae?)....
Just my experience living out here in the bush
