Scales are 1.0 to 7 mm long, usually green, yellowish or brown in colour and resemble shells glued to the plant. Female scales have neither wings nor legs. Females lay eggs under their scale. Some species give birth to young scales directly. Once hatched, the tiny scales, known as crawlers emerged from under the protective scale. They move in search of a feeding site and do not move afterwards. They suck sap on leaves and twigs. Their feeding may cause yellowing of leaves followed by leaf drop, poor growth, and dieback of branches. Two types of scales attack tea: soft and armoured scales.
Soft scales (Coccus spp; Saissetia coffeae) infest leaves and twigs. They cause damage by sucking sap from the plant and by excreting honeydew, causing growth of sooty mould. In heavy infestations leaves are heavily coated with sooty mould turning black. Heavy coating with sooty mould reduces photosynthesis and affects the quality of the leaves. Ants are usually associated with soft scales. They feed on the honeydew excreted by soft scales, preventing a build-up in sooty moulds, but also protecting the scales from natural enemies.
Armoured scales (Selanaspidus spp and Aspidiotus destructor) encrust foliage, the cause damage by sucking sap; they do not excrete honeydew.
- Conserve natural enemies. A large range of parasitic wasps and predators attacks scales. These natural enemies usually control scales. Outbreaks are generally related to the use of broad-spectrum pesticides that kill natural enemies, and or to the presence of large number of ants. If ants are protecting scales, try to control the ants by destroying their nests or spraying with soap mixed with water.
- Check infestation by scales. Peel off the hard shields and check whether there are living insects underneath. Dead empty shields can remain glued onto the plant for months, making it look like the scale population is much higher than it really is.
- If large numbers of living scales are present spray with light mineral oils. Sprays should target young stages of the scales. However, note that at high concentrations, mineral oils may be harmful to the plants. Oils should not be sprayed during periods of excessive heat or drought.
- At early stages of an outbreak cut and burn infested twigs and leaves.