Plum lecanium

The plum lecanium scale (Sphaerolecanium prunastri) is a significant pest belonging to the Hemiptera order and the Coccidae family. It is widely recognized as a serious threat to stone fruit orchards, where adult females appear as small, brownish, hemispherical protrusions on the bark, often mimicking the natural texture of the host tree.

This insect primarily attacks stone fruit trees, including plums, apricots, peaches, and sweet cherries. While it shows a strong preference for the Prunus genus, it can also infest other rosaceous plants, such as hawthorn and almond, making it a persistent concern for nursery and orchard managers across various climate zones.

The life cycle of Sphaerolecanium prunastri is univoltine, meaning it completes only one generation per year. The insect overwinters as second-instar nymphs sheltered in crevices or under the bark. As soon as spring temperatures rise, these nymphs migrate to branches to feed on sap. By early summer, they reach maturity, mate, and deposit eggs beneath the old cuticle, which serves as a protective shell.

The damage caused by the plum lecanium is twofold. Direct damage involves sap withdrawal, which leads to general tree decline, stunted growth, and loss of vigor. Indirect damage occurs when the pest excretes honeydew, a sugary substance that provides a medium for sooty mold to grow. This mold covers leaves and inhibits photosynthesis, significantly impacting fruit quality and yield.

Effective management requires a multi-stage approach. During the dormant season, pruning out infested branches and mechanical scraping of the bark can reduce the population. Early spring applications of horticultural oils are effective against overwintering nymphs. During the growing season, particularly when the crawlers (mobile nymphs) are active, systemic insecticides are applied to achieve high levels of control and prevent further infestation.