Pacific Pests, Pathogens and Weeds - Online edition

Pacific Pests, Pathogens, Weeds & Pesticides

Citrus snow scale (105)

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Photo 1. Female citrus snow scale, Unaspis citri. The female is very different from the male; it is oval, brown-black and 2 mm long, whereas the male is 1 mm, and white.

Photo 2. Male pupae on citron, citrus snow scale, Unaspis citri.

Diagram. Life-cycle of an armoured scale.

Summary
  • Worldwide distribution. Mostly, citrus, but the Pacific banana is a host. An important pest.
  • The scale has tube-like mouthparts, sucking sap from stems. Heavy infestations cause leaf fall and dieback.
  • Eggs hatch and “crawlers” walk or spread by wind, settle, feed and produce the protective armour, oyster-shaped in females, white and straight in males. Males become fly-like, without mouthparts, mate and die.
  • Natural enemies: ladybird beetles and parasitoid wasps.
  • Cultural control: scale-free nursery stock; Gliricidia windbreaks to protect from spread of "crawlers"; adequate nutrition.
  • Chemical control: use lime sulphur or wettable sulphur, leaving 30 days if also spraying oils (READ INSTRUCTIONS); alternatively, spot-spray infestations with horticultural oil, white oil, or soap solution (see Fact Sheet no. 56); avoid malathion and synthetic pyrethroids - they will kill natural enemies.
Common Name

Citrus snow scale, white louse scale

Scientific Name

Unaspis citri

AUTHOR Grahame Jackson
1Information from Waterhouse DF, Norris KR (1987) Unaspis citri (Comstock). Biological Control Pacific Prospects. Inkata Press; and CABI (undated ) Citrus snow scale Unaspis citri. Plantwise Knowledge Bank. (http://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=55685); and MAF Plant Health & Environment Laboratory (2011) Citrus Snow Scale (Unaspis citri): PaDIL - http://www.padil.gov.au; and from Buckley CR, Hodges AC (2017) Citrus snow scale. UF/IFAS Extension Service, University of Florida.(http://entnemdept.ufl.edu/creatures/orn/scales/citrus_snow_scale.htm). Photo 1 (and Diagram) Gillian Watson, Senior Insect Biosystematist, Plant Pest Diagnostics Branch, California Department of Food & Agriculture, Sacramento, CA, USA. Photo 2 Hamdeo. Scale covering a citron tree, killing it. (https://commons.wikimedia.org/wiki/File:Citrus_Scale_.jpg).

Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.

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