I recently discovered a mold/fungus disease growing on some plants. From searching google, it seems to be something called "sooty mold." I went to Home Depot and got an insect, disease and mite control spray. It doesn't seem to have helped. I'm a little worried as it appears to be spreading. Any ideas on what I can use to stop this and get it off my plants?
Sooty mold is typically a result of honeydew-secreting insects like aphids and scale. So if you want to fix the problem in the long term, you will need to find the insects and take care of them rather than worrying about the mold. The mold grows on the honeydew, it's not actually attacking the plant (although it looks ugly, and if too much of the leaves get covered up in it, it can cause them to not be able to photosynthesize properly). I don't see aphids or scale in your pictures...is this plant underneath a tree or some larger shrub? I've seen cases where there was a tree that had aphids and the honeydew dripped down onto the plants underneath and they developed sooty mold as a result even though the bugs weren't on them.
I can't find any honey-dew like substance on the plant. I was just assuming it was sooty mold. It's not under any plant or tree. I added another photo below that shows the entire plant area better. The black soot easily scrapes off the leaves.