If you think you have sooty mold, then you most likely have and insect problem.
Aphids and other sucking insects can produce alot of honeydew(poop!) that
collects on the leaves. In time, sooty mold will colonize on the poo. Taking
care of the insects takes care of the mold. Another thing I should mention is
that the honeydew may be dripping down from a larger plant, so inspect all the
plants in the general area.

Toad