Scale season

Scales are sap-sucking insects that come in many shapes and sizes, but they all share one characteristic – the adults build a coating that disguises and protects the pest beneath.

Generally, scales fall into two groups. Soft scales are the most easily seen, as they have a thicker coating that’s clearly obvious. Hard scales are smaller and less noticeable but can often cause more damage to the plant.

Some of the most common soft scales are white wax scale, pink wax scale and soft brown scale. Soft scales are often seen clustering along the mid-rib of the leaf. As well as sucking sap from the plant, most of these soft scales produce honeydew, a sticky substance that spreads out over the leaf. A black fungus called sooty mould (pictured) can grow on this layer. As well as looking ugly, this interferes with the plant’s ability to function.

Soft scales are easiest to control at this time of year because it’s their breeding season. The immobile mother scale lays her eggs under the protection of her scaly covering. After the babies hatch out, they head off to find a part of the plant where they can settle down and begin their sap-sucking life. They’re at their most vulnerable in this mobile stage.

Hard scales, which are flat and more difficult to control, don’t produce honeydew. Some hard scales (such as San Jose scale or rose scale) can cause accompanying dieback or discolouration on leaves or stems. Hard scales breed at any time of year, so it’s more difficult to catch them in their vulnerable juvenile stage.

Controlling scales


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