While it looks as if there may be some black spot, most of the
discolored places looked more like residue water on the leaves. The
leaves will sun burn more easily because the water acts like a prism
and concentrates the light in one place and the leaves can't react to
the light because of it. The scalded areas will be lighter in color,
then turn black. Try watering at the root and avoid sprinkling leaves,
during the heat of the day and too late in the afternoon and evening.