Horse chestnut scale

The horse chestnut scale (Pulvinaria betulae), also known as the birch scale, is a member of the Coccidae family within the Hemiptera order. Despite its name, it infests a wide range of deciduous trees and shrubs, including birch, maple, willow, lime, and various orchard species, acting as a significant sucking pest in gardens and parks.

The life cycle of this scale insect is univoltine, meaning there is one generation per year. The species overwinters as second-instar nymphs on the bark of host plants. As temperatures rise in spring, these nymphs mature into adult females. In early summer, the females produce white, cotton-like ovisacs on the undersides of branches, which contain hundreds of eggs, marking the most visible phase of the infestation.

Damage is caused by both nymphs and adults feeding on the sap of the host plant. This feeding process results in chlorosis, leaf distortion, and premature leaf drop. In severe infestations, the energy depletion of the host tree can cause twig dieback, reduced growth rates, and a significant decrease in the overall aesthetic value of ornamental specimens.

The pests excrete a sticky substance known as honeydew, which often covers the leaves and branches. This sugary deposit serves as a perfect substrate for sooty mold fungi, which coat the plant in a black, powdery layer. This mold inhibits photosynthesis, further weakening the tree and making it susceptible to other opportunistic pests and diseases.

Control strategies rely on a combination of chemical and cultural practices. Horticultural oils applied in early spring can effectively target overwintering nymphs. During the summer, when the mobile crawlers are active, systematic insecticides provide the best results. Promoting tree health through proper fertilization and pruning, along with supporting natural predators like ladybirds, remains the most sustainable approach.

• Regular inspection of bark and undersides of leaves.
• Application of horticultural oils in early spring.
• Timing insecticide applications with the crawler stage.
• Encouraging natural biological control agents.