Plum scale

Systematic position. Diaspidiotus degeneratus belongs to the order Hemiptera and the family Diaspididae. It is a specialized sap-sucking pest that protects itself with a hardened waxy shield, making it a challenging target for standard contact pesticides once the mature stage is reached.

Host plants. This species primarily infests members of the Rosaceae family. Plum (Prunus domestica) and related species such as cherry plum and peach are highly susceptible. Infestations typically start on young twigs and branches, eventually spreading to the trunk if not managed effectively.

Biology and life cycle. The pest typically completes one to two generations per year depending on environmental conditions. Overwintering occurs as second-instar nymphs on the bark. As temperatures rise in spring, nymphs resume feeding and mature into sessile females. These females produce eggs beneath their protective covers, and the subsequent crawler stage is the most mobile and vulnerable phase of their development.

Nature of damage. The insect damages host plants by inserting its stylet into the phloem and extracting nutrients. Heavy infestations result in severe localized necrosis of the bark, causing stunted shoot development, chlorosis of leaves, and significant branch dieback. Heavily infested trees show a marked decline in vigor and yield, often becoming more susceptible to wood-rotting pathogens.

Management and control. Integrated pest management (IPM) is essential for controlling this scale. Early spring dormant oil treatments are highly effective at smothering overwintering nymphs. During the growing season, monitoring for the presence of crawlers is critical. Chemical control should be timed to coincide with the crawler stage, as they lack the protective shield and are highly susceptible to systemic or contact insecticides.