Why does black powder appear on leaves?

The appearance of black powder on leaves is usually caused by sooty mold, a superficial fungus that grows on the honeydew produced by pests such as aphids, scale insects, whiteflies, or psyllids. Although it does not normally invade plant tissues, it can reduce photosynthesis and weaken plant growth. To eliminate it, it is essential to control the pest producing the honeydew first.