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.

Description

Female adults are sack-like with non-functioning legs or no legs at all. They lack a recognisable head, are wingless, usually sedentary, are long living and their main role is to lay eggs. Males (when they occur) are smaller and appear similar to whiteflies or gnats, they are non-feeding, short lived and possess one pair of wings. Their main role is to mate with females, although some species lay eggs without mating.

Some species lay live young, however eggs are more typically laid under the female and hatch as crawlers, which are mobile and feed on plants. The crawlers develop a waxy covering which is shed, this process can repeat up to three times before adults develop.

Scale feed on and damage growing shoots, leaves and fruit. Infestations can result in;

Reduced growth rates

Appearance of water stressed plants

Yellowing leaves and leaf drop

Dieback of stem (in severe cases)

Distorted fruit, and skin can become blemished.

Like aphids, scale excrete honeydew (sugary liquid) which promotes the growth of black sooty mould which can reduce photosynthesis. Ants feed on the honeydew and in return protect the scale by feeding on beneficial predatory insects.

Control

Management of scale should focus on prevention rather than control by implementing the following;

Plant scale free stock

Practice good crop/orchard hygiene e.g. removal of infested plants from growing areas, disinfecting pots etc

Encouraging beneficial predators by controlling ants and minimising insecticide use

Monitoring crops for presence of honeydew and scale infestations

Avoid movement of infested plant material within growing areas.

Scale are difficult to control with insecticides alone and if insecticide application is warranted, it should be targeted when crawlers are abundant.

Movento®, Confidor® 200 SC and Confidor Guard are all compatible with an integrated pest management (IPM) system. Movento is registered for scale control in citrus, grapes, mangoes, passionfruit and pome fruit, Confidor 200 SC for scale control in ornamentals and Confidor Guard for scale control in ornamentals and citrus.

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

Department of Primary Industries and Regional Development (DPIRD) ( 2018), ‘Aphids, mealybugs and scale’, https://www.agric.wa.gov.au/control-methods/aphids-mealybugs-and-scales?page=0%2C2

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

Kabashima, J, Dreistadt, S (2014) ‘ Scales’, Pest Notes, University of California, Publication 7408, http://ipm.ucanr.edu/PMG/PESTNOTES/pn7408.html