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.
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
Candidatus Lieberibactor asiaticus. Photo by Yuan-Min Shen, Taichung District Agricultural Research and Extension Station, Bugwood.org
Huanglongbing (HLB, citrus greening)
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
Colletotrichum acutatum SGO strain. Photo by Robert L. Anderson, USDA Forest Service, Bugwood.org
Post bloom fruit drop
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
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)
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
Anastrepha ludens (Mexican fruit fly). Photo by Jeffrey W. Lotz, Florida Department of Agriculture and Consumer Services, Bugwood.org
Exotic fruit flies
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
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
Homalodisca vitripennis. Photo by Johnny N. Dell, Bugwood.org
Glassy winged sharpshooter
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.
Citrus tristeza virus (Closterovirus). Photo by DPI NSW
Sweet orange stem-pitting
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)
Panonychus citri. Photo by Jim Baker, North Carolina State University, Bugwood.org
Citrus red mite
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.
Ceratitis capitata. Photo by Scott Bauer, USDA Agricultural Research Service, Bugwood.org
Queensland fruit fly
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