We have a young orange tree, and the leaves are turning black. What is causing this discoloration?
Look beyond the discoloration for piercing, sucking insects that are causing the discoloration. Often aphids, whiteflies and scale insects are feeding on the undersides of leaves and along stems and producing excreta that falls on the leaves. A sooty mold fungus then lives on the nutrient-rich excreta to produce the unsightly leaves. Some insect activity and sooty mold growth can usually be ignored, usually on older trees. If the insect activity and sooty mold coatings are slowing the growth of young trees, an oil spray available from your garden center can be used to treat the pests. The oil spray controls the insects and causes the sooty mold to slough off over a period of several weeks.
