White fungus on palm trees is actually webbing that is left by the spiraling whitefly. The flies create cotton-like white nests underneath the fronds of the palm trees. The nests are often mistaken for fungus.
If the palms are left untreated, sooty mold can develop on the leaves. The mold resembles fireplace soot and ashes and can prevent the leaves from absorbing adequate sunlight.
Soot mold caused by spiraling whitefly can easily be removed with dish soap and water. Palm trees can also be treated with gentle insecticides injected directly into the trunk. The insecticides effectively render the trees immune to spiraling whitefly infestation without causing damage.