Citrus snow scale

The Citrus snow scale (Unaspis citri) is a destructive sap-sucking pest belonging to the Diaspididae family of the order Hemiptera. It is recognized as one of the most persistent threats to citrus orchards worldwide, often creating dense white colonies on the trunks and branches of host trees.

The pest primarily infests plants in the genus Citrus, causing significant stress to orange, lemon, lime, and grapefruit trees. While it prefers the woody parts of the tree, heavy infestations can spread to the leaves and developing fruit, severely impairing the overall health and yield capacity of the plant.

The biological cycle is marked by distinct sexual dimorphism. The male scales are white, narrow, and elongated, forming the characteristic "snow-like" appearance on the bark. The females are brown, oyster-shaped, and better camouflaged. Depending on temperature, several generations can overlap, making them difficult to eradicate completely.

Feeding damage is caused by the insertion of piercing-sucking mouthparts into the plant tissue, which removes vital sap and injects toxins. This leads to chlorosis, leaf abscission, dieback of twigs, and severe bark splitting. If left untreated, young trees may suffer structural damage or die due to prolonged infestation.

Effective management requires a combination of strategies. Chemical control should be timed to target the mobile "crawler" stage, which is most vulnerable to systemic and contact insecticides. Additionally, the application of horticultural oils can suffocate the settled scales without leaving excessive chemical residues on the fruit.