Citrus canker
Citrus canker is a contagious disease caused by the bacteria Xanthomonas citri sub species citri, which affects all citrus plants.
In South Australia, it is a declared pest under the Plant Health Act 2009.
Background
The disease most likely originated in southeast Asia and has spread worldwide, to warm, moist, coastal regions. Citrus canker remains endemic in most areas where it is present.
It is recorded widely in Asia, the Middle East, some countries of central and western Africa, parts of the Pacific, South America, USA, and parts of North America.
Australia successfully eradicated 2 detections citrus canker. Western Australia was declared free of citrus canker on 22 November 2019 and the Northern Territory was declared free of it on 8 April 2021.
Citrus canker has never been detected in South Australia, and quarantine entry conditions are no longer required.
Impacts
The disease affects plants in the Rutaceae family, including those from the genera Citrus, Fortunella and Poncirus. The most virulent strain of the bacterium is a serious problem for grapefruit, lime, mandarin, tangerine, satsuma and kumquat. It also affects trifoliate orange rootstock.
Citrus canker attacks the leaves, twigs and fruit, causing blemishing, defoliation, and unripe fruit to drop. Over time, the plant can die.
Because the fruit is scarred, it can’t be sold. The costs to growers and consumers increase, while returns are lowered, threatening jobs and income across the citrus industry.
Citrus canker can be spread:
- over short distances by wind, rain, or wounds caused by feeding of the citrus leaf miner (Phyllocnistis citrella)
- across longer distances by people moving infected plant material or equipment.
The disease does not affect human or animal health.
Identification
Citrus canker presents as wart-like, rusty-brown spots on leaves, twigs and shoots. The cankers on leaves develop a distinctive bright yellow halo around them. Scabby cankers also appear on the fruit, as small, corky formations called lesions.
Inspect your citrus trees for symptoms, such as attacked leaves, flowers, young twigs, shoots, and fruit. Do not touch the lesions or move plant material off your property, which spreads the bacteria – report it immediately.