Sooty Mold

Sooty mold forms on the excretions of insect pests like scale, mealybug, aphids, and whiteflies (and many more). The pest might be feeding on the underside of the foliage on the blackened leaf. So you first need to examine this plant and surrounding plants carefully for pests. Look for insects or insect litter on the underside of the leaves. Scale can look bumpy on stems or like tiny bits of cotton. Some sucking insects, like lacebug, are very small and almost invisible, but you often see their “litter” under the leaves that look dusty, webby or dirty. Most sucking insects can be killed by spraying with insecticidal soap or horticultural oil, sprayed under the leaves of the infected plant. Do this two or three times. Once the insect is under control the sooty mold will go away.