Lecanium scale is a name given to an aggressive family of insects that can quickly spread and kill an affected tree within a couple of seasons unless they are treated. Female Lecanium scales lay several thousand eggs in late spring. The eggs will look like pollen and, as they hatch a few weeks later, the young scales spread and begin feeding on the sap of the host tree’s leaves and tender twigs and shoots. The females develop a hard scale which gives them their name. Males are a tiny flying insect with two long white tail-like strands. Hot weather exacerbates the infestations. Mosquito treatments remove natural predators and leave the Lecanium to multiply more rapidly.
Oak trees are particularly susceptible and the Oak Lecanium scale is a serious pest. However, other species such as hickory and birch and others are also susceptible to infestation. The European fruit lecanium, as its name suggests, infests fruit trees.
Symptoms: Infestation clusters on the lower leaf surfaces and twigs or bark of affected trees, a sticky dew dripping on the ground, or vehicles parked under the trees. These honeydew drippings will often attract ants and other insects.
More information: North Carolina State Extension
Oak lecanium scales and eggs on willow oak. Photo: SD Frank