Providing practical information to help you protect your farm from biosecurity risks

Citrus pests

 

High priority exotic pests

The following are high priority exotic pests of citrus, identified in the development of the Industry Biosecurity Plan for the Citrus Industry. Additional information is included in the fact sheets. These pests would have serious consequences if they were to become established in Australia.

While these are not the only exotic pests of the citrus industry, they have been assessed as potentially posing the greatest risk and the highest impact. Implementing biosecurity measures to control endemic pests will go a long way towards preventing exotic pests from entering and becoming established on your farm.

For a complete list of exotic pests of citrus, contact Citrus Australia for a copy of the industry biosecurity plan.

Citrus canker

citrus canker-5201025

Xanthomonas citri subsp. citri. Photo by Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org

  • Bacterium: Xanthomonas citri subsp. citri (previously known as X. axonopodis pv. citri and X. campestris pv. citri)
  • Found in over 30 countries in Asia, some Pacific and Indian Ocean islands, South America and USA (Florida)
  • Infects all young, actively growing leaves, twigs, stems, trunks, thorns and fruit of susceptible hosts
  • Lesions first appear as pin-point spots that become small, slightly raised pustules or blister-like eruptions
  • Lesions can be surrounded by a yellow halo and occur initially on the lower leaf surface
  • Symptoms exacerbated by leaf miner injury
  • Spores can be spread by wind blown rain, insects, workers and equipment, or via infected plant material
  • Has been eradicated from Australia on several occasions

Fact sheet

Huanglongbing (HLB, citrus greening)

Huanglongbing-5426934

Candidatus Lieberibactor asiaticus. Photo by Yuan-Min Shen, Taichung District Agricultural Research and Extension Station, Bugwood.org

  • Bacterium: Candidatus Liberibacter asiaticus (Asiatic form), Ca. L. africanus (African form) and Ca. L. americanus (South American form)
  • Huanglongbing can be found throughout Asia, the Middle East, Africa and North and South America
  • Leaves and shoot symptoms include yellow shoots; asymmetric, mottled (across veins) leaves; small upright chlorotic leaves; out of phase flushing; and branch dieback
  • Flower and fruit symptoms include unseasonal and heavy flowering on diseased branches; small, lopsided, bitter-tasting fruit with small, brown, aborted seeds and uneven colouring at maturity; and excessive fruit drop
  • Symptoms can be confused with mineral deficiencies and other endemic pathogens
  • Spread by infected plant material or by the Asiatic citrus psyllid (Diaphorina citri) or African citrus psyllid (Trioza erytreae)
  • All citrus and many citrus relatives are susceptible to Huanglongbing and host to its vectors

Fact sheet

Asiatic and African citrus psyllids

Asiatic citrus psyllid-5006083

Diaphorina citri. Photo by David Hall, USDA Agricultural Research Service, Bugwood.org

  • Psyllid (Hemiptera) – Diaphorina citri and Trioza erytreae
  • Sap-sucking psyllids that are serious pests of citrus
  • Transmit the disease Huanglongbing
  • Commonly found on young, tender flush leading to deformation and leaf drop
  • Spread locally by flight and over long distances via movement of plant material and strong winds
  • Asiatic citrus psyllid is present close to Australia in Indonesia, East Timor and Papua New Guinea
  • Asiatic citrus psyllid has previously entered Australia and was eradicated

Fact sheet

 

Citrus fruit borer

Citrus fruit borer

Citripestis sagittiferella. Photo by A. Beattie, University of Western Sydney

  • Larvae of moth: Citripestis sagittiferella
  • Found in Indonesia, Malaysia, Singapore and Thailand
  • Larvae (approx. 20 mm in length) are orange to dark reddish brown with dark brown head
  • Adult moth is grey-brown with yellow to grey-brown forewings and translucent hindwings (27 mm wingspan)
  • Larvae penetrate fruit causing in rotting and premature drop of fruit
  • Look for minute holes in, and cavities under fruit surface
  • Spread with infested plant material

Fact sheet

Citrus stubborn disease

Spiroplasma citri. Photo by J.M. Bové, INRA Centre de Recherches de Bordeaux, Bugwood.org

Spiroplasma citri. Photo by J.M. Bové, INRA Centre de Recherches de Bordeaux, Bugwood.org

  • Bacteria: Spiroplasma citri
  • Bacterial disease that leads to reduced fruit quality and yield
  • Symptoms include stunted growth; short, broad and upright leaves; lopsided or acorn-shaped fruit with possible inverted or uneven colouration
  • Transmitted between plants by feeding activities of leafhoppers or through transportation of infected plant material
  • Found throughout the Mediterranean basin and the Middle East, as well as parts of the USA, South America and northern Africa

Fact sheet

Citrus whitefly

Citrus whitefly-5194036

Dialeurodes citri. Photo by J. W. Lotz, Bugwood.org

  • Whitefly (Hemiptera): Dialeurodes citri
  • Found in Asia, Europe Africa and the Americas
  • Nymphs (<1 mm long) are flattened and can be easily mistaken for scales
  • Adults have creamy-yellow bodies with white wings, and are about 1 mm long
  • Eggs, nymphs and adults found on underside of leaves
  • Infested tissue covered in transparent honeydew
  • Potential vectors of citrus viruses
  • Adults can move short distances by flight and be transported long distance on infested plant material

Mal secco

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Phoma tracheiphila. Photo by G. Perrotta, Universita di Calabria, Bugwood.org

  • Fungus: Phoma tracheiphila
  • Found in the Mediterranean basin and Black Sea region, Israel, Turkey, Lebanon and parts of northern Africa
  • Infects most citrus including rootstocks, but most destructive on lemons and limes
  • Leaves wilt, dry up and fall followed by branch dieback
  • Infected bark on twigs may become silver grey, then rupture to show black fruiting bodies of the fungus
  • A red to orange internal discoloration develops in the trunk, brown in older tissue
  • Spores are spread by wind blown rain, insects, and workers or via infected plant material (can be symptomless)

Fact sheet

Mandarin stem-pitting

Mandarin stem-pitting-5202034

Citrus tristeza virus (Closterovirus). Photo by Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org

  • Virus: Citrus tristeza virus (Closterovirus)
  • Found in Thailand, Malaysia and Indonesia
  • Economically important virus with many strains that vary in severity
  • Grapefruit and sweet orange stem-pitting strains occur in Australia; however, the mandarin stem-pitting strain is absent from Australia
  • Severely affected trees may be stunted with a bushy appearance
  • Elongated pits are evident in the wood
  • Severe stem pitting has gum associated with fine pits
  • Spread by aphid vectors (brown and black citrus aphids) which are present in Australia, and through graft transmission or movement of infected plant material

Fact sheet

Citrus variegated chlorosis

Xylella fastidiosa subsp. pauca. Photo by Alexander Purcell, University of California,, Bugwood.org

Xylella fastidiosa subsp. pauca. Photo by Alexander Purcell, University of California,, Bugwood.org

  • Fungus: Xylella fastidiosa subsp. pauca
  • Caused by a bacterium that lives in the water conducting system (xylem) of citrus plants
  • Citrus plants show symptoms of zinc deficiency, particularly leaf yellowing, but also stunted growth, leaf lesions and small fruit with a hard rind
  • Can be spread via infected propagation material and potentially by leafhopper vectors such as the exotic glassy-winged sharpshooter (Homalodisca vitripennis)
  • Present in North America, Central America and some regions of South America

Fact sheet

Post bloom fruit drop

Post bloom fruit drop-0364036

Colletotrichum acutatum SGO strain. Photo by Robert L. Anderson, USDA Forest Service, Bugwood.org

  • Fungus: Colletotrichum acutatum SGO strain
  • Widespread throughout humid, subtropical citrus areas of the Americas
  • Serious crop losses in high rainfall areas
  • Infects flower petals and produces watersoaked lesions that turn pink, then orange brown as the
  • fungus sporulates
  • The fruitlet drops, leaving the floral disk, calyx and peduncle to form ‘buttons’
  • Leaves surrounding an infected inflorescence are small, chlorotic and twisted, with enlarged veins
  • Spores are spread by wind blown rain, insects, and workers or via infected plant material (can be symptomless)

Powdery mildew

Powdery mildew-5337063

Oidium tingitanium. Photo by Robert Lambe, Virginia Polytechnic Institute and State University, Bugwood.org

  • Fungi: Oidium tingitaninum or O. citri
  • Found in Asia, with reports from Central and South America and occasionally in California
  • Affects leaves, stems and fruit of all citrus cultivars
  • Whitish powdery patches of mildew form on the upper surface of leaves, which may then shrivel and fall
  • Older damage on leaves and fruit turns brown/grey
  • Mildew may cause premature leaf and fruit drop and dieback
  • Young affected fruit may fall prematurely. Remaining fruit develop brown irregular markings
  • Can be spread over large distances by wind currents

Exotic fruit flies

Anastrepha ludens (Mexican fruit fly). Photo by Jeffrey W. Lotz, Florida Department of Agriculture and Consumer Services, Bugwood.org

Anastrepha ludens (Mexican fruit fly). Photo by Jeffrey W. Lotz, Florida Department of Agriculture and Consumer Services, Bugwood.org

  • There are a number of Anastrepha and Bactrocera species not present in Australia which would have a severe impact on citrus and other industries and cause major restrictions on trade if they established here, including Mexican FF (Anastrepha ludens), Caribbean FF (A. suspensa), New Guinea FF (Bactrocera trivialis) and Oriental FF (B. dorsalis)
  • Flies damage citrus through larval feeding that leads to rotting and may lead to premature fruit drop
  • Spread via flight or wind currents or via the movement of fruit infested with larvae
  • Some are present in regions close to Australia, including Indonesia, East Timor and Papua New Guinea

Fact sheet

Exotic thrips

South African citrus thrips-1263057

Scirtothrips aurantii. Photo by D. Vincenot, Bugwood.org

  • Of particular concern to citrus are the exotic bean thrips (Caliothrips fasciatus), Florida flower thrips (Frankliniella bispinosa), blossom thrips (F. insularis) and California citrus thrips (Scirtothrips citri) and South African citrus thrips (S. aurantii), which is present in Queensland
  • Can seriously impact fruit quality, yield and market access
  • Are tiny (about 1 mm) with four wings and typically yellow/orange or greyish/black in colour
  • Can lead to brown scarring, curling and distortion of leaves, grey or brown scarring of fruit, premature flower and fruit drop
  • Spread by wind or via the movement of infected plants or plant material including fruit

Fact sheet

Glassy winged sharpshooter

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Homalodisca vitripennis. Photo by Johnny N. Dell, Bugwood.org

  • Leaf hopper (Hemiptera): Homalodisca vitripennis
  • Large xylem feeding leafhopper (about 12 mm) that causes direct damage to citrus through feeding activities
  • Vector of citrus variegated chlorosis (Xylella fastidiosa subsp. pauca), which is a serious disease of citrus
  • Spread through flight and via the movement of plants and propagation material infested with eggs and nymphs
  • Present throughout eastern and western USA, Mexico, French Polynesia Tahiti, Hawaii, Easter Island and the Cook Islands

 

Priority citrus pests already in Australia

There are a number of citrus pests which are currently present in parts of Australia, but are under official control to restrict their movement. The pests listed in the table below are not the only ones under official control, and any pest that is not normally present in your area should be reported without delay.

Sweet orange stem-pitting

Citrus tristeza virus (Closterovirus). Photo by DPI NSW

Citrus tristeza virus (Closterovirus). Photo by DPI NSW

  • Virus: Orange stem-pitting strain of Citrus tristeza virus (Closterovirus)
  • Found in Queensland
  • Infects all citrus, but principally damages sweet orange
  • Severely affected trees stunted with a bushy appearance
  • Twigs are brittle and easily bent
  • Elongated pits are evident in the wood
  • Severe stem pitting has gum associated with fine pits
  • Citrus nursery tree and budwood movement from Queensland is prohibited
  • Spread by aphids, especially the black and brown citrus aphids (Toxoptera aurantii and T.citricida)

 

Citrus red mite

Panonychus citri. Photo by Jim Baker, North Carolina State University, Bugwood.org

Panonychus citri. Photo by Jim Baker, North Carolina State University, Bugwood.org

  • Mite: Panonychus citri
  • Red to purple coloured, oval shaped mite that attacks all species and varieties of citrus.
  • Measures about 0.5 mm in length with four pairs of legs and bristles arising from bumps on the body.
  • Restricted in distribution to the Sydney metropolitan area and Central Coast of NSW.
  • Damages leaves, green bark and fruit and prefers light green, maturing foliage.
  • Scratch-like feeding marks lead to grey or silvery spots (stippling) on leaves and immature fruit, leading to an overall pale appearance, while injured mature oranges and lemons turn a pale straw yellow.
  • Severe infestations are more likely to occur in dry conditions and can lead to premature leaf and fruit drop as well as twig and branch dieback.
  • Spread via infested plant material such as citrus nursery trees and budwood.

Queensland fruit fly and Mediterranean fruit fly

Mediterranean fruit fly-5193027

  • Fly: Bactrocera tyroni (Queensland fruit fly; Qfly) and Ceratitis capitata (Mediterranean fruit fly; Med-fly)
  • Qfly is found in Eastern Australia and Med-fly is found in Western Australia
  • Maggots found in fresh fruit may be that of Qfly or Med-fly
  • Qfly (top) is wasp-like, red-brown with yellow marks, and about 8 mm long
  • Med-fly (bottom) is 3-5 mm long, light brown with mottled wings that have distinct brown bands extending to the wing tips
  • Qfly is most prevalent from September through to May and prefers humid conditions.
  • Most citrus varieties can be attacked by Qfly, in particular Meyer lemons, mandarin and grapefruit. All citrus varieties can be attacked by Medfly except some lemon varieties. Mandarins are particularly susceptible.
  • After laying eggs in the fruit, some necrosis may be visible around the puncture mark. This may be followed by decomposition of the fruit

Fact sheet