Pest Problems Explained: SCALE INSECT (Soft Scale)

Scale Insect (Soft Scale) Description:

There are two distinct groups of scale insects - soft scale and hard scale.

The most commonly found soft scales are Coccus hesperidum - the adults are 3-5mm long, green to brown in colour, oval- shaped and appear slightly flattened, and Saisettia coffeae - the adults are 5mm or longer in length, deep brown in colour and dome-shaped.

Hard scales have an armoured body, rather like a ladybird and do not produce honeydew. The biological control for these is not at present produced on a commercial basis in the UK, Defenders are therefore unable to offer a control for hard scale.

Scale Insect (Soft Scale) Damage:

The symptoms are similar to those of whitefly or aphids.

Soft scales are normally found congregating along leaf veins or stems. The scales feed on plant sap and produce large amounts of sticky honeydew.

Large populations will cause yellowing of the plant and defoliation. The honeydew results in the growth of black sooty moulds which ultimately kill the plant.

Scale Insect (Soft Scale) Life Cycle:

Soft scales produce a number of eggs over several days. The eggs are laid under the cover of the adult "scales" which offer protection during development. The adult dies once it has laid its eggs.

Eggs hatch into "crawlers", which are tiny legged creatures which disperse all over the plant and its foliage in search of a suitable site to settle down and become an immobile scale.

Scales grow relatively slowly and have a long life cycle. Saisettia coffeae takes about 95 days at 18ºC (64ºF) to complete it's life cycle.

Biological Control of Scale Insect (Soft Scale)

Soft scale can be controlled biologically in greenhouses or conservatories by Metaphycus helvolus.