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Mussel scale is a sap sucking insect that can be found on the bark of its host plants all year round.
Mussel scale on apple fruit
Mussel scale is a sap-sucking insect that lives mainly on the woody stems of its host plants. The small soft-bodied insects are concealed under shells or scales that resemble the shellfish of the same name. This is one of several species of scale insects encountered by gardeners.
Mussel scales are up to 3mm long and brownish black in colour. Their shape is similar to that of the shellfish known as mussels. Heavily infested plants will lack vigour and stems may dieback, especially on box. On apple, the scales sometimes spread onto fruits. Old dead scales often remain attached, so the scales can be seen throughout the year.
Light infestations of mussel scale are of little consequence but heavy attacks can affect the host plant's growth. When mussel scale spreads onto apple fruits it makes them less palatable, although the scales can be wiped off.
Light infestations can be tolerated without the need for control.
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Mussel scale has one generation a year. Female scales deposit their eggs underneath their bodies during late summer-early autumn, so they are concealed by the shell or scale that covers the insect. The eggs overwinter and hatch in late May-June, when the scale nymphs crawl around for a while and can be distributed on wind currents, before selecting somewhere to feed. This is mainly on the bark but scales can develop on the fruits of apple and Cotoneaster. The scales reach the adult stage in late July-August.
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