Oyster shell scale

The Oyster shell scale (Lepidosaphes ulmi) is a significant pest belonging to the order Hemiptera and the family Diaspididae. It is a cosmopolitan species, commonly found in temperate regions, known for its distinct protective armor that resembles the shape of a tiny oyster shell.

This insect is a highly polyphagous pest with a vast host range. It infests a wide variety of deciduous trees and shrubs, including apple, pear, plum, and black currant. It is also frequently found on various landscape plants, such as ash, lilac, and cotoneaster, which can act as secondary sources of infestation.

The life cycle consists of a single generation per year. The insect overwinters in the egg stage beneath the protective scales of dead females. Upon hatching, the first-instar nymphs, known as crawlers, emerge from beneath the scale, migrate to suitable feeding sites on the bark, and become permanently sessile as they initiate feeding and scale formation.

Feeding damage is caused by the insertion of piercing-sucking mouthparts into the bark and cambium layer. Severe infestations can lead to significant sap loss, stunted growth, yellowing foliage, branch dieback, and, if left untreated, the gradual decline and potential death of the host tree.

Integrated pest management strategies are crucial for control. Early spring applications of horticultural oils can effectively suffocate overwintering eggs. During the crawler stage, which coincides with the post-bloom period, contact insecticides or systemic products are required to manage the population before they develop their protective covers.

• Pruning and destroying heavily infested branches
• Application of dormant horticultural oils
• Monitoring for crawler emergence in late spring
• Using systemic insecticides during the active feeding phase