The disyllabic pronunciation \ˈfō-lij\ is very common. Some commentators insist that foliage requires a trisyllabic pronunciation because of its spelling, but words of a similar pattern such as carriage and marriage do not fall under their prescription. The pronunciation \ˈfȯi-lij\ is disapproved because it suggests the transposition of the l and i in the spelling. It is not as common as \ˈfō-lij\ and may be associated with the nonstandard spelling foilage.
Examples of FOLIAGE
a tree with pretty foliage
the thick green foliage of the jungle
Origin of FOLIAGE
Middle French fuellage, from foille leaf — more at foil