Many types of scales infest jasmine shrubs and vines. They lay their eggs on the leaves or bark, and in spring to midsummer the young scales, called crawlers, settle on leaves and twigs. The small (1/10-inch), soft-bodied young feed by sucking sap from the plant. The legs usually atrophy, and a hard crusty or waxy shell develops over the body. Mature female scales lay their eggs underneath their shells. Some species of scales that infest jasmine are unable to digest fully all the sugar in the plant sap, and they excrete the excess in a fluid called honeydew. A sooty mold fungus may develop on the honeydew, causing the jasmine leaves to appear black and dirty.

This common black mold is found on a wide variety of plants in the garden. It is caused by any of several species of fungi that grow on the sugary material left on plants by aphids, mealybugs, scales, whiteflies, and other insects that suck sap from the plant. The insects cannot fully digest all the sugar in the sap, and they excrete the excess in a fluid called honeydew, which drops onto the leaves below. The sooty mold fungus develops on the honeydew, causing the jasmine leaves to appear black and dirty. Sooty mold is unsightly but is fairly harmless because it does not attack the leaf directly. Extremely heavy infestations prevent light from reaching the leaf, so the leaf produces fewer nutrients and may turn yellow. The presence of sooty mold indicates that the jasmine or another plant near it is infested with insects.

This insect is a common pest of many garden and greenhouse plants. The four-winged adult lays eggs on the undersides of leaves. The larvae are flat, oval, and semitransparent. They feed for about a month before changing to the adult form. Both larval and adult forms suck sap from the leaves. The larvae are more damaging because they feed more heavily. Adults and larvae cannot fully digest all the sugar in the plant sap, and they excrete the excess in a fluid called honeydew, which often drops onto the leaves below. A sooty mold fungus may develop on the honeydew. In warm-winter areas these insects can be active year-round.