Citrus canker

​Citrus canker (Xanthomonas citri subsp. citri) is a serious bacterial disease of commercial varieties of citrus. The disease affects the leaves, twigs and fruit causing the leaves to drop and fruit to fall to the ground before it ripens.

Situation overview

The nationally coordinated response to locate and remove all traces of citrus canker is progressing, with on-ground response teams in place in the Northern Territory (NT) and Western Australia (WA).

There are currently a limited number of infected premises, with eleven in the NT and three in northern WA. This number is likely to increase as ongoing tracing information identifies the location of risk plants. Having found these infected plants provides confidence that the tracing system is working.

Available evidence indicates that citrus canker is still primarily restricted to potted plants in the home and garden sector, and all infected premises are linked to a single source premise in Darwin. 

The majority of citrus canker infections have been found on three different varieties of lime.

Surveillance of citrus production areas so far has not detected the disease in any citrus orchards.

Tracing information continues to be shared with all other jurisdictions, allowing for inspections and thorough diagnostic testing to be done quickly and effectively. As a result of these activities, citrus canker has not been detected in any other states or in the ACT.

The NT and WA have put movement controls and quarantine measures in place to contain the disease.

All other jurisdictions have introduced domestic movement controls to prevent the entry of citrus canker hosts and carriers, plants and plant material, soil, equipment and machinery, from the NT. However, stringent measures are in place to allow for the safe interstate trade of fruit.

More on movement restrictions.

Citrus canker does not affect human or animal health and infected fruit remains safe to be consumed.

Citrus canker response strategy

A nationally agreed Response Plan is in place which aims to stop citrus canker by tracing and destroying infected plants and any hosts within 600 metres. As with all response plans, they are reviewed as the response progresses to make sure it is on track. There are also ‘triggers’ in the response plan.  When a trigger is reached the plan must be reassessed by the CCEPP and NMG. Some (not all) trigger points for this response plan are listed below:

  • the distribution of citrus canker has not been effectively determined or ‘delimited’ - for example if the disease is confirmed at a site that cannot be linked to a known source, or if it is found in another state or territory where the disease has not previously been confirmed.
  • Information collected during the response does not support key assumptions made about the disease in determining the response strategy. These assumptions may relate to disease prevalence, effectiveness of the containment measures, or the ability to prove that an area is free of the disease.
  • operational delivery is not tracking as intended.
  • community or industry activity hinders the effective delivery of the response.

The Response Plan was developed in line with national arrangements, with technical advice provided by the Consultative Committee on Emergency Plant Pests (CCEPP). The plan was endorsed by the National Management Group (NMG) in May 2018.  This group also monitors expenditure so the response does not exceed the agreed budget and that it remains cost beneficial (i.e. the costs to eradicate provide a greater benefit).

Affected industry groups (that are Parties to the Emergency Plant Pest Response Deed) are represented in both the CCEPP and NMG.

Working groups

The Response Plan is part of broader approach to this citrus canker incursion. Three specialist working groups have been established to help guide the response plan activities.   

Response Strategy Working Group

This group is focused on developing incursion scenarios and risk based response strategies that may effectively achieve eradication. They have assessed four plausible scenarios against the outcomes of the Response Plan that is underway, and are providing advice to the CCEPP. Priority areas of action for this group include surveying areas of interest outside the mapped Greater Rural Darwin Area and assessing the likely, total number of infected plants at the source premise. 

Tracing Working Group

‘Tracing’ is the term used to describe the process for locating areas of possible biosecurity risk through the movement of potentially infested plants, machinery, tools and other items which may spread the disease.

A Tracing Working Group has been established to consider all the tracing procedures and analysis being undertaken across the states and territories. This includes developing strategies to trace material that has left the source premise. This group is critical to targeting the response activities to areas that are at most risk of disease.

Surveillance Working Group

The surveillance working group which will develop a national surveillance strategy.  This strategy, combined with the tracing data, will help us determine where citrus canker is absent in Australia. We can then make a decision on proof of freedom which underpins our ability to show our trading partners that we are free of the disease  (either that it has been fully eradicated or is confined to a limited area). 

The surveillance strategy will address each of the risks that arise from plants being exposed to those plants that have come from citrus canker infected premises (including those currently identified in in the Northern Territory, Western Australia, New South Wales and Queensland).  This may include surveillance being undertaken in the response, such as:

  1. Traced property surveillance
  2. Evidence of absence surveillance on orchard/nursery
  3. Area of interest surveillance (no direct link to IP)
  4. Infected property surveillance
  5. Restricted area surveillance.

The plan will be informed by residual risk assessments being done by the Tracing Working Group.

The surveillance plans will be integrated with a communications and engagement strategy that increases awareness and promotes early detection and reporting of any diseased plants during, and potentially post, the eradication response. 

Operations

The response strategy working group is time limited and is expected to contribute to the development of the final eradication response strategy.  Its role and function will be reviewed by CCEPP at the end of September 2018.

It is coordinated by the Department of Agriculture and Water Resources (DAWR) and its membership includes experts from:

  • DAWR
  • Citrus Australia
  • the NT Department of Primary Industry and Resources
  • the WA Department of Industries and Regional Development
  • the QLD  Department of Agriculture and Fisheries.
  • SA Department of Primary Industries and Regions
  • NSW Department of Primary Industries
  • VIC Department of Economic Development, Jobs, Transport and Resources

Progress of field activities

To date, surveillance has been conducted on 3,500 premises in the Northern Territory, and 460 in Western Australia. This surveillance has shown infected plants are limited to those supplied from the source property in Darwin. There has been no spread from these infected plants to other host plants.

The other states have also conducted surveillance and testing as a result of the tracing information they received from the NT. In total around plant 7,000 traces have been investigated across Australia, and no canker has been found. The premises that have been surveyed included retail outlets, residential properties, and production nurseries. There are no traces to commercial citrus orchards, however, they have also been inspected as a precaution.

Between the NT and WA, more than 12,000 plants have been destroyed, and disposed of in accordance with the agreed response strategy for citrus canker. Destruction of host plants within the WA restricted areas is very close to completion. For the NT, the scale of destruction is much larger and expected to take longer but is being progressed.

Biosecurity and reporting

As a precautionary measure, we are asking people from the Northern Territory or from northern Western Australia with citrus plants to check them for signs of citrus canker. Plants that were purchased locally within the last 12 months are of particular concern.



Advice for growers

Growers can put on-farm biosecurity measures in place to reduce the chance of pests and disease getting into their orchards. These include:

  • using pest-free propagation material and seedlings, sourced from a reputable supplier
  • putting up farm biosecurity signs on gates and fences to manage visitors coming onto your property
  • avoiding the sharing equipment
  • keeping equipment and vehicles clean and free of plant matter
  • wearing clean clothing before visiting other growers’ properties
  • teaching farm workers are aware of on-farm hygiene practices, knowing what to look for and how to report unusual pests and diseases.

You can find out more about on-farm biosecurity, and order your signs at farmbiosecurity.com.au.

Reporting

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

Signs of infection can look similar to other bacterial diseases that are known in northern Australia.  All suspect symptoms must be reported.

If you think you have a plant with citrus canker, or if you have recently sourced citrus plants from the Northern Territory or northern Western Australia in the last 12 months, please contact the Exotic Plant Pest Hotline on 1800 084 881. This will put you in touch with the department of primary industries or agriculture in your state or territory.

You should not collect a sample or move the suspect plant.   

Most states have an app or mechanism for submitting a photo for preliminary diagnosis. The photo should be a clear image of the suspect plant, the disease symptoms and the plant’s label, if you still have it.

Interstate travellers

Interstate travellers also have a role in preventing the spread of pests and diseases. Quarantine bins are in place for travellers on all major routes out of the restricted area in Western Australia.  Please place all citrus fruit or citrus plant material in these bins before you leave the area.

Do not take fruit, whole plants or plant cuttings into another state or territory without checking first.  You can do this on the Interstate Quarantine website.

Movement restrictions

Northern Territory

The Northern Territory has special restrictions on the movement of host plants. The control area covers the greater Darwin area and beyond, south to Adelaide River, east to Kakadu and west to Dundee.  In addition, six restricted areas have been declared around properties found to have infected plants.

In Katherine, the restricted area covers a defined area in Cossack.

Plants susceptible to citrus canker, and products such as fruit and leaves, are not allowed out of this area.

See the Northern Territory’s Department of Primary Industry and Resources website for more information including maps.

Western Australia

On 12 June 2018 the Western Australia Department of Primary Industries and Regional Development declared three Restricted Areas at the Kununurra and Wyndham sites where infected plants have been found.

This means that all citrus trees and parts of these trees, including fruit, cannot be moved into, out of or within the Restricted Areas. Propagation and planting of these plants is also prohibited.

Broader Control Areas remain in place, covering a 50km radius around both Kununurra and Wyndham, preventing the movement of citrus plants and fruit from these areas.

Find out more about the WA Quarantine area including maps.

About citrus canker

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

The disease is native to South East Asia. It infects a plant through wounds and natural openings on leaves, stems, thorns and fruit. 

It presents as lesions or cankers at infection sites and severely impacts fruit quality and yield. 

Symptoms are exacerbated by injury caused by feeding activity of the insect citrus leaf miner, which is the larvae of a small moth widely distributed in Australia.

The symptoms of citrus canker include blister-like lesions on both sides of the leaves that are raised, tan to brown in colour, and are surrounded by an oily, water-soaked margin and a yellow ring or halo. Large or older lesions may have a crater-like appearance.

Premature fruit drop can occur, along with defoliation, twig dieback and general tree decline. In severe cases, it can lead to tree death.

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 cyclones, or by people moving infected plant material or equipment.

Plant Health Australia citrus canker fact sheet

National Diagnostic Protocol for Asiatic Citrus Canker

History of citrus canker in Australia

Citrus canker has previously been detected in Australia but has been eradicated in each instance.

The first recorded outbreak of citrus canker was in the Northern Territory in 1912.

The initial occurrence of the disease took 11 years to fully eradicate.

In 1984, a program was initiated to eradicate citrus canker from Thursday Island. Over a two year period a total of 10 citrus trees were found to have canker symptoms and were destroyed. No symptoms of citrus canker have been observed on Thursday Island since February 1986, and the disease was declared eradicated in September 1988.

Citrus canker was detected in the Northern Territory again in 1991 at Lambell's Lagoon, about 50 kilometres from Darwin, and affected a small number of pomelo citrus trees.

All affected trees were destroyed, and the area was intensively monitored for two years. Citrus canker was officially declared eradicated in the Northern Territory in 1995. The Department of Primary Industry and Resources has continued to undertake regular surveillance and testing since then to help ensure the Territory remained citrus canker free.

The disease was also detected on several commercial citrus orchards in Emerald, Queensland, in 2004.  Eradication of the outbreak and restoration of country freedom for the disease was declared in January 2009.

Comparisons to the Emerald citrus canker incursion

This current incursion is different to the incident that occurred in Emerald in 2004. The source of the outbreak in Emerald was in an orchard in a commercial citrus area. The current incident in the NT and WA is in citrus plants that are intended to be grown in patio pots or in residential backyards. 

The 600 metre destruction zone that is being implemented, is designed to manage the potential natural spread from any infected plants, and is based on the scientific evidence available from previous outbreaks in Australia, and from overseas.

The agreed response plan is constantly being reviewed and adjusted as the incident changes or when new information becomes available.

Plant imports

Only budwood material for use as nursery stock can be imported to Australia. This material must go into the Australian government’s Post-Entry Quarantine facility for a minimum of 24 months and is subject to screening and testing for plant pathogens.

Plants are regularly inspected for citrus canker. During growth in quarantine, plants are subject to disease elimination treatments, and only shoot tip grafted plants free of diseases, are released from biosecurity control.

Since January 2013 there have been 23 permits issued for the import of nursery stock. There were no detections of citrus canker during the disease screening period.

More information

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