Citrus Canker

Citrus canker is a contagious disease of citrus (and some other plant species of the citrus family, Rutaceae) caused by the bacteria Xanthomonas citri subsp. citri. Infected trees display unsightly lesions which can form on leaves, fruit and stems.

Trees infected with the disease may suffer from low vigour and a reduction in fruit quality and quantity. Citrus canker is a serious disease impacting on citrus production and is the subject of a number of control and eradication programs around the world.

Citrus canker can cause abnormal leaf fall, die back, discolouration, poor growth and economic loss. In severe cases infected trees will die.

The disease is widespread in many tropical and subtropical citrus-growing areas of the world. Australia is currently free of citrus canker but has previously been detected in 1912 and 1991 in Darwin, Northern Territory (NT) and in Queensland on Thursday Island in 1984 and Emerald in 2004 and has been subsequently eradicated.

Many citrus crops can be affected by citrus canker, including:

  • limes
  • lemon
  • citron
  • mandarin
  • orange
  • grapefruit.

Citrus canker can be spread rapidly over short distances, particularly in tropical and subtropical climates by wind-blown rain.  Overhead irrigation systems can also spread the disease. Long distance spread occurs through flooding, cyclones, or by people moving infected plant material or equipment.

For more information on citrus canker read the Plant Health Australia fact sheet:

Symptoms

Citrus canker appears as raised spongy lesions on leaves, twigs and fruit, which gradually increase in size to 5-10 mm over several months. Eventually the lesions collapse forming a crater-like appearance. The lesions become surrounded by characteristic yellow halos, and the raised edges of the lesion may appear “slimy”.

Citrus canker - Sublime symptoms Citrus canker - - Symptoms on branchCitrus canker - - Symptoms on citrus plantCitrus canker - - Symptoms on citrus leaf

Cause

Citrus canker is caused by a bacterial infection which causes spongy, eruptive lesions on fruit, leaves, and branches of citrus.

Biosecurity and reporting

Early detection, reporting and not moving infected plants is vital, and will give us the best chance of eradicating this disease.

You should not collect a sample or move the suspect plant, instead report the symptoms to the NT Department of Primary Industry and Resources (DPIR).

Signs of infection can look similar to other bacterial diseases that are known in northern Australia, therefore it is vital for all diagnosis to follow the national protocol.

Following strong evidence citrus canker has been detected in Darwin; the NSW Government has issued a Control Order prohibiting the entry of all citrus from the Northern Territory including plants, fruit and leaves.

The New South Wales Department of Primary Industries (DPI) issued the Biosecurity (Citrus Canker) Control Order 2018, which will be in effect from 20 April 2018 for 18 months (unless revoked prior).

If you think you have a plant with citrus canker, or if you have recently bought citrus plants from a Darwin or Palmerston retail nursery, please contact the department by:

When phoning the hotline you can arrange to submit a photo for preliminary diagnosis. The photo should be a clear image of the suspect plant and the plant’s label, if you still have it.

Crops affected

Many citrus crops can be affected by citrus canker. These include limes, lemon, citron, mandarin, orange, and grapefruit.

Spread

The disease can be spread by wind and rain, landscaping equipment, people through hands, clothing, or equipment and through infected or exposed plants or plant parts.

How you can help

DPIR is urging the public to check their citrus plants  (409.3 kb) for the suspected Citrus Canker disease.

Early detection, reporting and not moving infected plants is vital, and will give the department the best chance of eradicating this disease.

Plants that were purchased over the past 12 months are of particular concern.

We are currently asking all Territorians with citrus plants to please urgently check them for symptoms, not to move the plants and to contact the department if you think it may be infected with the disease.

If you think you have a plant with citrus canker, or if you have recently bought citrus plants from a Darwin or Palmerston retail nursery, please contact the department by:

You should not collect a sample or move the suspect plant.  When phoning the hotline you can arrange to submit a photo for preliminary diagnosis. The photo should be a clear image of the suspect plant and the plant’s label, if you still have it.

Biosecurity is everyone’s business and we need to work together to manage the risk and eradicate citrus canker. Government and industry are taking this extremely seriously and are working together to manage this situation.

Frequently asked questions

Questions

Answers

What does citrus canker look like?

Symptoms on leaves and fruit are brown, raised lesions surrounded by an oily, water-soaked margin and a yellow ring or halo. Old lesions in leaves may fall out, creating a shot-hole effect.

What is citrus canker?

Citrus canker is a contagious disease of citrus (and some other plant species of the Rutaceae family) caused by the bacteria Xanthomonas citri subsp. citri. Infected trees display unsightly lesions which can form on leaves, fruit and stems.

Trees infected with the disease may suffer from low vigour and a reduction in fruit quality and quantity. Citrus canker is a serious disease impacting on citrus production and is the subject of a number of control and eradication programs around the world.

How did we get it?

Like many plant diseases there are a number of pathways that citrus canker could have entered the NT through.

The department’s scientists and experts are investigating all options to try and identify the origin.

Does it affect all citrus plants?

Citrus canker is a contagious disease caused by the bacteria Xanthomonas citri subsp. citri which can affect all citrus plants.

Are there human health impacts?

No, citrus canker does not harm humans or animals and fruit remains safe for consumption.

How long does the bacteria survive for?

Inoculum remains in the lesions of plants from year to year, and are the primary source of new infections. Bacteria can also survive on straw or mulch, or in soil.

Bacteria from lesions are spread throughout the plant by rainfall. In rain storms, bacteria can be carried between trees, up to 100m. The disease can remain in infected rotting plant material, such as mulches and become active again in periods of high rainfall and warm weather.

The disease cannot survive in the soil, it must have contact with a plant host.

It is not transmitted by seeds.

How does the disease spread?

The disease  can be spread by wind and rain, landscaping equipment, people through hands, clothing, or equipment and through infected or exposed plants or plant parts.

Does citrus canker occur in other parts of Australia?

Citrus canker has previously been found in Australia, however it has been eradicated each time.

Are all NT citrus plants affected?

DPIR are currently undertaking tracing and surveillance to understand what plants are affected.

Does the NT have enough biosecurity monitoring in place to protect the local industry?

Biosecurity is everyone’s responsibility – from growers to backyard gardeners, scientists and consumers.

We all have a responsibility to be alert for new pests and diseases to help protect our vital agricultural industries. The NT takes its biosecurity responsibilities very seriously and has been quick to act when outbreaks occur.

What restrictions are in place to stop the spread?

All national biosecurity protocol procedures are being considered at this stage.

How do I report Citrus Canker?

Contact the Department of Primary Industry and Resources by:

Last updated: 11 May 2018