Oak lecanium scale

Systematic position. The oak lecanium scale (Parthenolecanium rufulum) belongs to the order Hemiptera and the family Coccidae. It is a sap-sucking insect that specializes in parasitizing woody plants, primarily members of the Fagaceae family, causing long-term damage to the health of the tree.

Host plants. The primary hosts for this pest are oak trees (Quercus spp.). However, it is also frequently found on chestnut (Castanea), beech (Fagus), and hornbeam (Carpinus). It prefers to inhabit branches in woodlands, urban parks, and landscape plantations where the host plants are present.

Biology and life cycle. The species completes one generation per year. Second-instar nymphs spend the winter in the crevices of the tree bark. In the spring, these nymphs resume feeding and mature into adult females. After laying eggs beneath their convex test (scale), the eggs hatch into mobile nymphs known as crawlers, which disperse across the tree to settle on new growth.

Type of damage. The scale insects feed by extracting sap from the phloem of young branches. This constant drain of nutrients weakens the tree, leading to stunted shoot growth, chlorosis, and potential leaf drop. Furthermore, the large amount of honeydew produced by the scales promotes the growth of sooty mold, which coats the leaves and restricts photosynthesis.

Control measures. Management strategies focus on chemical application during the crawler stage, as they lack the protective hard shell of the adults. Integrated pest management (IPM) is recommended, including maintaining tree vigor, pruning heavily infested branches, and supporting natural biological controls like parasitic wasps and ladybird beetles that prey on scale insects.

• Visual inspection of branches for scale clusters.
• Application of horticultural oils during the dormant season.
• Use of systemic insecticides during the peak of crawler activity.
• Pruning to remove high concentrations of overwintering insects.