Citrus canker decreases fruit quality and yield. The disease leads to defoliation, twig dieback, blemished fruit and premature fruit drop. In severe cases, it can cause tree death.
The disease causes small, round blister-like formations on leaves, branches, stems, new shoots and fruit. The canker lesions can develop within seven days of infection on leaves. Fruit are susceptible up to 90 days after petal fall. Young plants and seedlings are more susceptible to Citrus canker.
On stems and branches
|Bright yellow spots on the underside of the leaf occur first followed by raised brownish lesions on both sides of the leaves. These then become rough, cracked and corky. The canker may be surrounded by a water-soaked yellow or chlorotic halo.||Crater-like lesions form on the surface surrounded by an oily, water-soaked margin or yellow halo, which can expand to 10mm. They may be scattered or several lesions can occur together in an irregular pattern. In young fruit an ooze of resinous substance may be observed.||Lesions are light to dark brown, raised and corky, that eventually become dry and scabby. They can vary in size from 5 to 10mm. The appearance of symptoms on stems often indicates infection for a long time.|
The canker lesions ooze bacteria when wet, which can infect new growth, and be dispersed over short distances through wind, rain splash and overhead irrigation.
Long distance spread can occur through flooding and cyclones, and human assisted movement of clothes, equipment and infected plant material (including budwood, rootstock seedling, budded trees).
Plants are infected when bacteria or bacteria spores enter wounds and natural openings on leaves, growing shoots and fruit. The disease can be spread by birds, insects and humans, particularly when trees are wet.
The bacteria can survive in diseased plant tissue as well as in soil. It can over-winter in angular shoots, and then become active again the following season.
Declared Pest Category
This plant pathogen has been declared to be a prohibited organism under section 12 of the Biosecurity and Agriculture Management Act 2007 (the Act) as Xanthomonas axonopodis subsp. citri .
Affects some Rutaceous plant species, particularly citrus varieties (such as grapefruit, lime, lemon, mandarin, orange, cumquat and their hybrids) and non-citrus hosts such as Australian round lime (refer to host list).
Present throughout Asia and South America, on some islands in the Pacific and Indian Oceans, as well as some parts of the Middle East and in the USA (Florida).
There have been several outbreaks in Australia: in the Northern Territory in 1912, 1991 and 1993 and Queensland in 2004. All were successfully eradicated.
2018 detection and department response
In May 2018, citrus canker was detected in imported citrus plants at two retails businesses at Kununurra and at one premise in Wyndham. These plants originated from the Northern Territory.
The Department of Primary Industries and Regional Development commenced an emergency response to the detection and imposed restrictions on the movement of citrus plants and fruit around both Kununurra and Wyndham. Extensive surveillance and tracing activities throughout the north west of Western Australia followed, and no further evidence of the disease was found.
As part of its response, the department removed more than 1500 citrus plants from properties that were in areas immediately around the sites with infected plants.
Department staff continued inspection activities in 2019 and, upon declaring Western Australia free of citrus canker in November 2019, had visited more than 13,000 properties. On 22 November 2019, the quarantine notice was revoked.
The department would like to thank the community and the WA citrus industry for their support for the response, and for their commitment to ensuring the disease didn't spread.