You're right - I looked at the genus name, had no clue what it was, and moved on.

Here in the US, we get a black sooty mold that usually comes about as a result of whiteflies or sometimes other sucking pests.

Neem oil is a good all-purpose treatment, but I can't recall where neem trees grow, perhaps Australia?

The black sooty mold that watergal refers to is often the poop of the pest that is sucking on the hibiscus. Just plain old soap and water a few times will break it down and spray it off with water after a few treatments the sooty mold should be gone. It doesn't really cause a problem to the plant but is a symptom of the real problem. In Hawaii I ran in to it and if I controlled the ants that feed on this honeydew excretement that I didn't have much of a problem. Aphids is what I would often encounter as the culprit but white flies and mealybugs can do much the same if they get out of hand.
I hope this gives you some ideas to share with your friend and good luck and Happy Growing
David

I will pass on your helpful information to my friend ..

Evidently Neem Oil and the Neem Tree are indigenous to India .. but as there are many Indians doing business in West Africa, my friend might be lucky in finding some ! ;-))

Cheers

David