I have a 10 year old Dancy mandarin tree in the ground. It had a scale infestation which resulted in sooty mold. I have been spraying with neem oil and fish emulsion mixture every week for 3 weeks and the scales seem to have disappeared. But the ants and the black powdery stuff (sooty mold?) remain to an extent. What should I do now? Thanks in advance for your help.

The sooty mold is probably caused by the seceration from aphids. The oil spray should take care of the mold. Try a good ant bait to get rid of the ants. The ants feed the secretration from the aphids.

Thanks buddinman. Will try to set an ant trap near the tree.