Citrus canker
 Xanthomonas citri subsp. citri. Photo by Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org |
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- 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)
 Candidatus Lieberibactor asiaticus. Photo by Yuan-Min Shen, Taichung District Agricultural Research and Extension Station, Bugwood.org |
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- 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
 Diaphorina citri. Photo by David Hall, USDA Agricultural Research Service, Bugwood.org |
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- 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
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Citrus fruit borer
 Citripestis sagittiferella. Photo by A. Beattie, University of Western Sydney |
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- 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 |
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- 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
 Dialeurodes citri. Photo by J. W. Lotz, Bugwood.org |
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- 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
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Mal secco
 Phoma tracheiphila. Photo by G. Perrotta, Universita di Calabria, Bugwood.org |
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- 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
 Citrus tristeza virus (Closterovirus). Photo by Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org |
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- 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 |
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- 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
 Colletotrichum acutatum SGO strain. Photo by Robert L. Anderson, USDA Forest Service, Bugwood.org |
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- 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)
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Powdery mildew
 Oidium tingitanium. Photo by Robert Lambe, Virginia Polytechnic Institute and State University, Bugwood.org |
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- 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
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Exotic fruit flies
 Anastrepha ludens (Mexican fruit fly). Photo by Jeffrey W. Lotz, Florida Department of Agriculture and Consumer Services, Bugwood.org |
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- 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
 Scirtothrips aurantii. Photo by D. Vincenot, Bugwood.org |
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- 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
 Homalodisca vitripennis. Photo by Johnny N. Dell, Bugwood.org |
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- 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
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