Citrus greening (huanglongbing)

Have you seen citrus greening symptoms? Be on the lookout for symptoms and report them to Biosecurity Queensland on 13 25 23. Early detection and reporting of symptoms are the key elements in controlling the pest.

Photograph showing symptoms of citrus greening on leaves

Symptoms of citrus greening.

General information

Huanglongbing, also known as ´citrus greening´, is a bacterial disease that is lethal to citrus. Huanglongbing and the psyllid insects that transmit the disease are not known to occur in Australia. It is prohibited matter in Queensland under the Biosecurity Act 2014.

Huanglongbing occurs in many parts of the world, including Asia, parts of North, Central and South America, and Africa. Closer to Australia, it is found in Indonesia, East Timor and Papua New Guinea. Huanglongbing is a serious threat to citrus production areas worldwide.

The psyllid insects are the Asiatic citrus psyllid (Diaphorina citri) and the African citrus psyllid (Trioza erytreae).

Please help by looking for and reporting any suspicious symptoms.

Overview

What causes huanglongbing?

Huanglongbing is caused by Candidatus Liberibacter bacteria. The bacteria live in the host plant´s food conducting tissue (phloem), where they impede the movement of nutrients.

What does it look like?

In citrus, leaf symptoms include:

  • leaves with blotchy mottling, that is not uniform across the leaf
  • yellowing of leaves and growing shoots that stand out from the normally green canopy
  • small, upright, yellowish leaves with thickened leaf midribs and veins, sometimes resembling deficiencies (e.g. zinc or boron nutrient deficiency symptoms)
  • unseasonal leaf flushing that is out of phase with healthy trees
  • leaf drop and dieback of branches.

Citrus fruit s symptoms are:

  • out-of-season flowering and fruiting on infected branches
  • small, lopsided fruit with small, dark, aborted seeds
  • unevenly coloured mature fruit (particularly sweet oranges and mandarins in temperate and subtropical regions)
  • premature and excessive fruit drop
  • bitter tasting fruit.

Citrus trees:

  • become progressively unthrifty
  • have leaf and fruit drop
  • develop branch dieback and root rot, leading to eventual tree death.
Hosts

All species and cultivars of citrus are affected, such as orange, grapefruit, mandarin, tangelo, kumquat, lemon, lime, pomelo, trifoliate orange and tangelo, and native citrus. Mock orange or orange jasmine (Murraya spp.) can also be a host plant.

Spread of disease

Long-distance spread can occur by the movement of infected citrus planting material, or by the movement of plant material infested with huanglongbing infected psyllids.

Movement of other host plants such as orange jasmine (Murraya spp.) and curry leaf (Bergera koenigii) also pose a risk of introducing huanglongbing-infected Asiatic citrus psyllids.

The Australian Quarantine and Inspection Service closely regulates approved importations of host plant material and monitors for illegal plant movement.

Tropical storms and cyclones could also lead to long distance spread of Asiatic citrus psyllids from Indonesia and Papua New Guinea to northern Australia.

Management and quarantine

Regularly check citrus for the presence of huanglongbing symptoms such as leaf yellowing on one branch or sectors of the tree and uneven blotchy mottling of leaves, leaf drop, dieback and misshapen fruit. Report suspicious symptoms.

There are simple steps you can take to protect your farm:

  • Purchase healthy propagation material [c1] [CAP2] from reputable nurseries that use Auscitrus seed and budwood, which is routinely tested for disease.
  • Check new plants to make sure they are pest and disease free.
  • Check your crop. Ensure you and your farm workers are familiar with symptoms of huanglongbing and the insects that spread it.
  • Report anything unusual.
Human health

There are no impacts on human health from huanglongbing-affected plants and fruit. Although bitter tasting, the fruit is safe to eat.

Reference and acknowledgement
  • Patricia Barkley (Citrus Australia Limited)
  • Andrew Beattie (University of Western Sydney)
  • Sandra Hardy (NSW Department of Primary Industries)
  • Andrew Miles (Department of Agriculture, Fishers and Forestry)
  • Ceri Pearce (Department of Agriculture, Fishers and Forestry)

Related information

Citrus conditions causing symptoms similar to huanglongbing fact sheet
(PDF, 611.0KB)

Last updated 29 April 2013