What are those little brown humps that cover my oak twigs? These are lecanium scale insects.
The lecanium scale can be debilitating to the host plant, rarely killing it. The insect draws sap from the tree, thus reducing the tree’s resources. A heavy infestation can stress a tree greatly and may cause thinning of the foliage.
The insect has various life stages. The brown humps are mature females. Eggs are laid within the shell and hatch in the early spring. Some generations produce winged males and females, and this is how the insect spreads. When the eggs hatch, the young are called crawlers. They migrate to the leaves to feed before returning to the twigs to settle down. During this early life stage feeding, the insects produce a sticky substance called honeydew that can coat leaves and objects under the trees. A mold called sooty mold grows on the honeydew making the leaves and twigs turn black, reducing the photosynthesis capacity of the leaves.
Control is important when infestations are heavy. Have a Tree Shepherds arborist correctly identify the insect and recommend a treatment.