differencesnounsplant-physiology
OED defines these words as:
foliage: the leaves (of a plant or tree) collectively; leafage
leafage: leaves collectively; foliage
Both of them seem to mean almost the same.
Google NGram gives the following picture:
So, aside from the fact that leafage is much less widespread in comparison with foliage, is there any difference between their semantics or the way they are used?
A rock is bigger, possibly immovable, you couldn't throw it with one hand, at a pinch you might be able to with two.
Above, a Google Image result for "Rock", below, for "Stone"
Note that a boulder is probably bigger than a rock1.
Below, a boulder
Oh, also note that rocks and boulders are made from stone.
(This answer is mildly tongue in cheek)
1 Notable exception: Uluru/Ayre's Rock.
In common usage, imbalance is the noun meaning the state of being not balanced, while unbalance is the verb meaning to cause the loss of balance. In the context stated, the noun form should be used.
Best Answer
The two words are pretty much synonyms in all contexts, but if a distinction can ever be made, perhaps leafage sometimes alludes slightly more to the individual leaves (albeit, collectively). I don't advance this possibility particularly strongly, because I don't think I really believe it myself.
Thus you might see leafage pattern used relatively more often to refer to the "average" pattern on each leaf, as opposed to the foliage pattern referring to the overall disposition of leaves on the plant. By "relatively" there, I mean after allowing for the fact that "foliage" is much more common in the first place.
The general advice would simply be; forget about using the word "leafage". There are no contexts where "foliage" would actually be wrong, and using the uncommon word may stand out as "odd".