Ficus tree scale diseases are a result of scale insects, which are very difficult to detect since they are about the size of a grain of ground pepper. These small insects can, however, create a number of other problems for your tree, and these secondary infections can alert you to the fact that you have a ficus tree scale problem. Knowing what to look for when it comes to scale insects will help you attack the root of the problem rather than just treating recurring symptoms.
Scale insects feed on the sap of the ficus trees. As they gnaw away at the bark of stems and twigs, they may cause the tree to start leaking sticky sap from its wounds. In addition, the bugs themselves make a sticky syrup that can attract ants to your tree. The presence of sap or ants may alert you to a scale disease problem. You should remove the sap as much as possible using a cotton swab dipped in rubbing alcohol, then spray down the tree (including the tops and bottoms of the leaves) with neem oil, to prevent reinfection.
Since scale insects ooze a sweet syrup, molds and mildews can also infect your ficus as a result of a scale disease. Sooty mold is black and looks powdery, like chimney soot. Remove the affected parts of the plant and throw them away to prevent reinfection. Swab down the plant with an alcohol swab and treat it with neem oil to get rid of the scale disease.
Mealybugs are a particularly rapacious scale infection that can actually kill your plant if allowed to go unchecked. Remove limited infections by swabbing the plant with rubbing alcohol. If there are too many bugs to remove by hand, you can give your ficus a shower in lukewarm water after spraying it down with a diluted soap mixture to break down the mealybug's waxy body barrier. Keep the ficus away from other plants until you are sure that the infection is gone.