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.
Citrus canker does not affect human or animal health.
The nationally coordinated response to locate and remove plants affected by citrus canker is on-track.
Citrus canker was detected in Darwin, Northern Territory (NT), in April 2018, and subsequently in northern Western Australia (WA).
The initial response phase focused on locating and removing all known traces of the disease.
Surveillance was conducted on over 9,000 premises in the Northern Territory and in Western Australia. This surveillance has shown that all infected plants found to date, were supplied from the one source property in Darwin. There has been no spread from these infected plants to other host plants.
The other states 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 citrus canker has been found outside the NT or WA. The premises surveyed were retail outlets, residential properties, and production nurseries. There are no traces to commercial citrus orchards, however, they have also been inspected as a precaution.
Movement controls and quarantine measures to contain the disease remain in place in the NT and WA.
The response to this incident is being managed under national response arrangements, with technical advice provided by the Consultative Committee on Emergency Plant Pests (CCEPP). The National Management Group (NMG) is responsible for endorsing the citrus canker response plan, based on recommendations made by CCEPP. NMG also monitors expenditure so the response does not exceed the agreed budget and that it remains cost beneficial (i.e. the costs to eradicate the disease 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.
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. We are interested in citrus plants purchased (or received as a gift) since 1 January 2017.
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.
Phone the Exotic Plant Pest Hotline on 1800 084 881 from anywhere in Australia to report citrus canker.
Signs of infection can look similar to other bacterial diseases that are known in northern Australia but if you see a plant with suspect symptoms, this must be reported.
We are particularly interested in citrus plants that have been obtained since 1 January 2017, and were sourced from the NT or northern WA.
You may also be able to report using your phone, with most states having 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.
Early detection, reporting and not moving infected plants is vital, and will give us the best chance of eradicating this disease.
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.
The Northern Territory has special restrictions on the movement of host plants. The Darwin control area covers the greater Darwin area and beyond, south to Adelaide River, east to Kakadu and west to Dundee. In addition, twelve restricted areas have been declared around properties found to have infected plants in the greater Darwin control area.
In Katherine, the restricted area covers a defined area in Cossack. A control area has been established around the Katherine restricted area.
There are movement restrictions on plants susceptible to citrus canker, and products such as fruit and leaves, in the control and restricted areas.
See the Northern Territory’s Department of Primary Industry and Resources website for more information including maps.
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.
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.
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.