Red Scale

Aonidiella aurantii

Belonging to the armoured scale group, red scale, also known as citrus red scale or Californian scale, is the most common and damaging scale affecting citrus in Australia. It occurs on a wide range of hosts including citrus, passionfruit, carob, roses, papaya and olives.

Refer to links below for more information on different scale species.

Description

Red scale is concealed by a thin round protective cover, underneath lies a flat, soft, creamy-yellow insect. Females are small (2 mm), circular and reddish brown, while males are short lived, elongated, paler, smaller and have wings. Females give birth to live young which remain under the protective cover until they emerge as yellow-reddish crawlers, just visible and similar in appearance to females. Crawlers move to find food where they remain and go through several moults, emerging later as male or females.

Damage from red scale can result in severe downgrades in fruit quality or rejection. It is a declared pest in some countries and therefore its presence can affect export markets. Heavy infestations can weaken trees, causing yield loss and in severe cases trees may die.

Control

Parasitic wasps play a vital role in the control of red scale. Two species; Aphytis lignanensis and Aphytis melinus, are commercially available and target red scale. For optimum control it is recommended to release A. lignanensis from March to April and A. melinus from November to March. Other beneficial insects include ladybird beetles, chilocorus beetles (a ladybird beetle) and predatory mites - minimise the use of broad-spectrum insecticides to encourage these populations.

Crop monitoring is essential, if fruit infestations of red scale reach 10 per cent or more in early varieties or 15-25 per cent of fruit in later varieties, appropriate control measures should be taken. These include releasing parasitic wasps or a well-timed application of an insecticide when crawler numbers are high. Movento® is soft on most beneficial insects, including parasitic wasps, and is best applied when pests are at the crawler stage. Both Movento and Confidor® Guard are registered for control of red scale in citrus.

Related Pests

Scale

Parthenolecanium persicae (Grapevine scale), Lepiddosaphes beckii - (Mussel scale), Ceroplastes rubens (Pink wax scale), Aonidiella aurantia - (Red scale), Quadraspidiotus perniciosus - (San Jose scale), Coccus hesperidum - (Soft brown scale)

There are more than 20 families of scale including hard (armoured) scale, soft scale, mealybugs and felt scales. Whilst all scale insects are sap sucking, a large amount of diversity exists between species. Soft scales do not have a separate protective cover, in contrast the protective cover in hard scales is not attached to the soft insect body. They infest a large group of host plants including citrus, mangoes, passionfruit, pome fruit, stone fruit, ornamentals and grapes. The term scale refers to the coating over the back of the insect.

Refer to links below for more information on different scale species.

Grapevine scale

Parthenolecanium persicae

Grapevine scale is an increasing problem for Australian grape producers where, in high numbers, they can reduce the vigour of grapevines. These soft scale feed on sap secreting honeydew which in addition to attracting ants, commonly leads to the development of sooty mould. This mould can form on all parts of the vine, including the fruit, and can lead to the grapes being downgraded or rejected by the market.

Refer to links below for more information on different scale species.

Pink wax scale

Ceroplastes rubens

A type of soft scale, pink wax scale is commonly found on the upper surface of leaves along the midrib in crops including citrus, mangos, avocados and custard apples. While frequently found in orchards, pink wax scale generally causes minor damage.

Refer to links below for more information on different scale species.

Soft brown scale

Coccus hesperidum

Soft brown scale (SBS), also commonly known as brown soft scale, is common in tropical and sub-tropical citrus growing areas of Australia. It infests many hosts including citrus, papaya and ornamental plants. SBS belong to the soft scale group, unlike hard scale species, they do not have a separate scale cover. SBS are known for producing large amounts of honeydew and subsequently are commonly accompanied by sooty mould and ants.

Refer to links below for more information on different scale species.

References

Broughton, B (2007), ‘Scale in citrus’, Department of Agriculture and Food Farmnote 243, https://citrusaustralia.com.au/wp-content/uploads/fn2007_citrusscale_sbroughton.pdf

Department of Primary Industries and Regional Development (DPIRD) (2018), ‘Aphids, mealybugs and scale’, DPRID, https://www.agric.wa.gov.au/control-methods/aphids-mealybugs-and-scales?nopaging=1

Department of Agriculture and Fisheries (DAF) (2017), ‘Red Scale’, Queensland Government, https://www.daf.qld.gov.au/business-priorities/agriculture/plants/fruit-vegetable/insect-pests/red-scale

Mo, J (2002), ‘Red Scale’, Department of Primary Industries (DPI) NSW, https://www.dpi.nsw.gov.au/agriculture/horticulture/citrus/content/insects-diseases-disorders-and-biosecurity/insect-pest-articles/a-timing-guide-for-the-management-of-red-scale