Hawthorn scale

Hawthorn scale (Palaeolecanium bituberculatum) is a member of the Coccidae family within the order Hemiptera. This pest is a specialized sap-sucking insect that primarily infests the bark of woody stems, often going unnoticed until the infestation becomes severe and visible symptoms appear on the host tree.

The primary hosts of this scale insect include a variety of pome and stone fruit trees. Apple, pear, hawthorn, and plum are among the most frequently attacked species. The insects prefer to settle in the crevices of bark on smaller branches, where they remain stationary for most of their adult life cycle.

The biological cycle follows a univoltine pattern, meaning one generation per year. Second-instar larvae overwinter on the bark, emerging in early spring as temperatures rise. After maturation, females lay eggs under their protective, hardened coverings. By late spring or early summer, the nymphs, known as crawlers, emerge to settle in new locations on the tree.

Damage is caused by the extraction of large amounts of plant sap, which leads to general tree debilitation. In cases of high population density, infested trees exhibit stunted growth, chlorosis, and reduced fruit yields. Furthermore, the insects excrete honeydew, which provides an ideal substrate for the growth of sooty mold, blocking light and reducing photosynthesis.

Management strategies require an integrated approach to maintain orchard health. Proper cultural practices, such as pruning to improve canopy aeration and removing heavily infested branches, are essential. During the dormant season, oil-based treatments can suffocate overwintering larvae, while chemical applications during the crawler emergence phase provide the most effective suppression of the population.