Walnut scale

Systematic position: The insect belongs to the order Hemiptera, family Diaspididae. The species Diaspidiotus juglansregiae, commonly known as the walnut scale, is a significant polyphagous pest capable of spreading rapidly in various climatic conditions, causing severe economic losses in orchards.

Host plants: This pest has a wide range of host plants. While it is particularly notorious for damaging walnut trees, it also infests a variety of pome and stone fruits, including apple, pear, peach, plum, and apricot, as well as various ornamental trees and shrubs.

Biology and lifecycle: The insect typically overwinters as fertilized adult females or second-instar nymphs sheltered under protective scales on the bark of branches and trunks. In spring, as temperatures rise, the females produce crawlers. Depending on the climate, the species may complete one or two generations per year, with crawlers actively moving to new feeding sites before establishing their permanent protective covers.

Damage and economic impact: By sucking sap from plant tissues, the walnut scale weakens the host tree significantly. Symptoms include bark cracking, premature leaf drop, stunted shoot growth, and dieback of twigs. Heavy infestations can lead to the complete decline and death of branches, severely reducing fruit yield and overall tree vigor.

Control measures: A successful integrated pest management strategy includes several key tactics.

• Application of dormant oil sprays in late winter or early spring to smother overwintering stages.
• Use of systemic insecticides timed specifically to target the mobile crawler stage.
• Sanitary pruning of heavily infested branches to reduce the pest population.
• Encouragement of beneficial predatory insects and parasitoid wasps that naturally control scale populations.