The black sooty mold is probably the result of sucking insect damage such as aphids, mealybugs or scale and the white powdery substance is likely mildew or it might be due to whitefly. For sucking insects and mildew spray with a suffocant such as a horticultural oil but spray in the early evening to avoid burning the foliage during the heat of the day. There are also chemical systemics available for ornamental plants as another option, but you would need to get rid of the current problem first and the systemic would be for future control. If you have whitefly, spray with Spinosad, another organic control for chewing insects. Spray after the bees have returned to their hives in the early evening. Once the spray is dried, it is not harmful to beneficial insects.