Mussel scale

Lepidosaphes beckii

Mussel scale (MS), also known as citrus mussel scale or purple scale, is one of 11 scale species found in Australian citrus. MS is part of the hard scale (armoured) group as they have a waxy protective cover which is detached from their soft body. They do not produce honeydew like other many other scale species.

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

Description

Female MS are small (3-4 mm), mussel shaped, with a purplish to brown protective cover over the soft body. Males are smaller and lighter in colour and unlike females, they have a pupal stage and wings, they lack mouthparts and are short lived. Eggs are laid under the outer cover and hatch into mobile feeding crawlers in early spring. Once settled in a suitable feeding spot, they develop a waxy cover and after several moults, adults form.

MS prefer shady or sheltered positions and so are often found on the underside of leaves and sometimes young stems. They suck sap causing leaf drop and dieback and on ripe fruit green spots form from feeding, making the fruit unappealing and often resulting in quality downgrades.

Control

Beneficial predators such as parasitic wasps are efficient at controlling MS although fruit damage can occur in citrus if beneficial predator populations have been wiped out. Therefore, the use of broad-spectrum insecticides (particularly synthetic pyrethroids) should be avoided.

Sourcing pest free material, removal of infested plants and providing adequate nutrition and water so plants are healthy and well cared for is important. Orchards should be monitored for the presence of scale, and when 20 per cent or more of fruit are infested with one or more scale species, control options should be implemented.

Adult MS can be difficult to control with some insecticides due to the protection offered by the hard scale. For best control a well-timed application early in the season when crawlers are abundant may assist with control. Due to overlapping generations, more than one spray may be required.

Movento® 240 SC Insecticide is registered for MS control in citrus and with its systemic activity and unique mode of action works well to control juvenile crawlers under bark and in hard to reach places on the tree. Movento is soft on beneficial insects when used as directed and for best results should be applied after flowering has been completed, and early in the season prior to significant population build-up.

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.

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.

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

Food and Fertiliser Technology Centre (FFTC) (2003), ‘Important pests of Citrus in Asia’, FFTC, http://www.fftc.agnet.org/library.php?func=view&id=20110707233340

Jackson, G (2017), ‘Citrus mussel scale’, Pacific Pests and Pathogens - Fact Sheets, http://www.pestnet.org/fact_sheets/citrus_mussel_scale_340.htm

Manners, A (2016), ‘Scale insects. A difficult problem that can be managed’, Horticulture Innovation Australia, https://www.horticulture.com.au/globalassets/hort-innovation/resource-assets/ny15002-scale-insects-pest-mgmt-plan.pdf