Azaleas – Black Lumpy Crust
Q: I have no idea what is affecting my azaleas. The stems are covered by a black lumpy crust, and all the leaves except the ones at the ends of the stems are black.
A: When lower leaves on a shrub all turn black, I immediately think of sucking insects that might cause this, like thrips, spider mites, mealy bugs, aphids, scale, and whiteflies. The first two are tiny and can’t do what you’ve described. But the other four can. Based on my experience, the black stems and leaves are caused by a bad infestation of whiteflies and scale insects. Both creatures are famous for sucking more sap from a plant than they can digest. They excrete the excess as a sticky liquid called honeydew. The honeydew coats everything, and a sooty mold grows on it to make things black. Check my website for tips on how to control the insects.