I have a small Japanese Maple on my patio planted in a container (3'x3'). It has been doing great with nice green leaves and new leaves appearing (reddish color). Then one day I noticed all the leaves have brown edges all around the entire leave. The tree has an east exposure with early morning sun till about 1 p.m. Any ideas on what could have cause this in an "over night" time frame? And what is the cure, if any? Thanks!