General information

Citrus canker is a contagious disease of citrus (and some other plant species of the Rutaceae family) caused by the bacteria Xanthomonas axonopodis pathovar 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.

Symptoms

The bacterium enters the plant tissue and causes the development of blister-like formations (lesions).

Lesions are usually raised, coloured tan to brown, surrounded by an oily, water-soaked margin and a yellow ring or halo. Large or older lesions may have a crater-like appearance.

Leaf, fruit and stem tissue may be infected. Leaf tissue offers more opportunity for infection and as such typically displays the most numerous lesions over time. It is unusual to see multiple lesions on fruit or stems if lesions are not present on leaves.

What to do if you find symptoms

Phone DEEDI on 13 25 23 for advice.

Do not touch the lesions or move plant material off your property - this can spread the disease.

Susceptible plants (hosts)

All citrus cultivars can be affected (e.g. orange, lemon, lime, grapefruit, mandarin, kumquat, tangelo, pomelo and citrus rootstock). However, some cultivars of citrus more readily develop canker lesions than others.

Citrus canker can also affect some native Australian Rutaceae species, such as Citrus glauca (desert lime), Acronychia acidula (lemon aspen), Micromelum minutum (lime berry) and Murraya paniculata var. ovatifoliolata (native mock orange). Other plants such as wampee (Clausena lansium), white sapote (Casimiroa edulis) and elephant apple (Feronia limonia) are also known hosts.

Infection and spread

The canker lesions ooze bacteria when wet. Over short distances this bacterial ooze can be spread by rain splash or overhead irrigation systems. Citrus canker can be spread over longer distances on equipment (vehicles, tools, mechanical hedgers, sprayers, gardening equipment) and people (hands, shoes and clothing).

Movement of infected plant material, or airborne movement of bacteria as an aerosol or debris during severe weather events (where strong winds and rain are present), can also spread the disease further.

Illegal importation of infected plant material poses the greatest risk of introducing this disease into Australia. The Australian Quarantine and Inspection Service closely monitors for illegal plant movements and regulates approved host plant imports.

Distribution

The disease is widespread in many tropical and subtropical citrus-growing areas of the world. Australia is currently free of citrus canker. Outbreaks in Australia are rare, with the last detection in Emerald, Queensland, in May 2005. This area was declared free of citrus canker in 2009.

Significance

Serious economic disease affecting the citrus industry.

Human health

Citrus canker is a plant disease. It is not harmful to people or animals.

Management and quarantine

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

• To avoid introducing citrus canker on to your property, establish new plantings with healthy plant material from reputable nurseries that use Auscitrus seed and budwood, which is routinely tested for a range of diseases. On receipt of any new plants, check that they are pest and disease free. If citrus canker is detected, isolate suspect nursery stock from healthy plants until official checks are completed.
• Keep your farm clean. Use good sanitation and hygiene practices. Remember that workers, visitors, vehicles and equipment can spread diseases. Make sure equipment is clean before it enters your farm.
• If you have been to an overseas country that has citrus canker, do not wear your travel clothes into your orchard until after they have been washed in hot soapy water.
• Make sure that you and your farm workers are familiar with the symptoms of citrus canker. Regularly check your orchard and report any unusual or unfamiliar symptoms.