Plum scale

Plum scale (Diaspidiotus prunorum) is a destructive pest of stone fruit trees, belonging to the family Diaspididae in the order Hemiptera. This insect is well-adapted to survive on host plants by creating a tough, waxy shield that covers its body, making it highly resistant to environmental stressors and many direct contact treatments.

The primary hosts for this pest include plum, apricot, peach, and cherry trees. Infestations typically start on the bark of young twigs and branches, eventually spreading to the trunk. The pest remains stationary for most of its life cycle, continuously extracting nutrients from the vascular tissue of the host plant.

The life cycle of the species is univoltine, meaning it produces one generation per year. The insect overwinters as second-instar larvae protected by a scale cover. As temperatures rise in spring, the larvae resume feeding and reach maturity. During summer, the female produces crawlers (the active first-instar stage) which migrate to new areas of the tree to establish their own feeding sites.

Feeding by the plum scale causes significant physiological stress to the tree. Symptoms and damage include:

• stunted shoot growth and malformed branches;
• yellowing and premature dropping of foliage;
• cracking and necrosis of the bark;
• increased susceptibility to secondary fungal infections;
• significant reduction in overall yield and fruit quality.

Management requires a strategic approach targeting the most vulnerable stages of the pest. Dormant oil sprays are highly effective when applied in late winter or early spring to smother overwintering larvae. During the growing season, monitoring for the emergence of crawlers is essential for timing the application of systemic or contact insecticides. Cultural practices, such as pruning infected wood and ensuring proper tree spacing, help manage populations effectively.