Greasy spots are fungus that oftentimes appear as yellow-brownish spots on the underside of a leaf. Use liquid Copper fungicide to stop the fungus from spreading. In Minnesota, this has been a big problem for me, even more so than the pests.
Sooty Mold is a type of citrus fungus commonly found in hot, humid environments. It’s far less likely to be found in arid climates.
Greasy spots can be treated through a couple applications of copper fungicide. Read the directions on the package on how much to add in your sprayer reservoir. Dilute with water. My particular cooper fungicide has a blue color added to it so it’s easy to tell which plants and leaves on those plants have been sprayed.