Scale
/skeɪl/
Definition
Scale refers to a group of small sap-sucking insect pests that attach to stems, leaves, or branches and feed by piercing plant tissue. Adults are often immobile and protected by a waxy or shell-like covering, which makes them look like bumps rather than typical insects. In gardening, the term usually includes soft scales and armored scales, both of which can weaken plants and may cause yellowing, sticky honeydew, or dieback.
Effects on Plants
- Sap loss and weakening: When scale feeds, it removes plant sap, which can slow growth, reduce vigor, and cause yellowing or leaf drop, especially on stressed or heavily infested plants.
- Honeydew and sooty mold: Many kinds of scale excrete honeydew, a sticky sugar-rich waste that encourages black sooty mold on leaves and stems and can reduce light reaching the plant surface.
- Common hiding places: Infestations often build up on stems, leaf undersides, nodes, and along veins, where the insects are protected and easy to miss during routine plant checks.
- Management challenges: The waxy or hard covering of scale can shield it from contact treatments, so control is usually more effective when aimed at the mobile young stage, called crawlers.
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