PLANT PEST
Timothy Schubert, Florida Department of Agriculture and Consumer Services, Bugwood.org.
Citrus canker
Exotic to Australia, previous incursions have been eradicated from Australia
Features: A bacterial disease that causes significant damage to citrus species, ruining crops and preventing trade
Where it's from: Over 30 countries in Asia, South America, United
How it spreads: Importation of infected plants or plant material; local spread by insects, water splash, movement of infected plants, fruit, equipment or personal items
At risk: Commercial citrus species and related plants
Keep it out
Citrus canker, caused by the bacterium Xanthomonas citri subsp. citri, affects the leaves, twigs and fruit of citrus plants causing the leaves to drop and unripe fruit to fall to the ground. All types of citrus are affected by the disease.
Citrus canker is most severe in hot, wet areas. The infected sites ooze sap which can carry the disease from tree to tree by irrigation or rain splash. Citrus canker can spread quickly over long distances on infected citrus fruits and leaves, as well as on people and equipment.
There is no cure for the disease, so any infected trees have to be destroyed and orchards replanted at great cost. If citrus canker established in Australia, trading partners are likely to reject any fruit that could carry the disease to avoid importing the disease as well. Australia’s citrus industry and the communities it supports would be threatened.
Citrus canker has been found in Australia more than once before, and each time it was eradicated after years of effort. the most recent invasion occurred in April 2018, in Darwin, Northern Territory and was also found in northern Western Australia. A nationally coordinated response was undertaken in those areas to locate and remove plants affected by the disease to eradicate it once again. This response was successful and in April 2021 citrus canker was officially declared eradicated from Australia.
The islands of Torres Strait provide a potential pathway for serious pests such as citrus canker to get to Australia from countries to our north.
Importing goods
To keep citrus canker out of Australia, never ignore Australia’s strict biosecurity rules.
Import shipments may need to be treated and certified, so before you import, check our Biosecurity Import Conditions system (BICON).
Travelling interstate
With recent outbreaks of the disease in the north of Australia, interstate travellers have a role to play in preventing the spread of citrus canker.
Do not take fruit, whole plants or plant cuttings into another state or territory without checking first. Before you travel or move house, look up your journey on the Australian Interstate Quarantine website to see the restrictions that apply.
What to look for
- Warty, rust-brown to tan spots (cankers) on leaves, twigs and shoots.
- Spots on leaves are rough to touch and are surrounded by a yellow halo.
- Scabby cankers on the fruit.
Where to look
Look for symptoms on:
- all citrus varieties (orange, lemon, lime, grapefruit, mandarin, kumquat, tangelo, pomelo and citrus rootstock)
- related native species including desert lime, lemon aspen, lime berry, and native mock orange
- wampee
- white sapote
- elephant apple.
Importers
Importation of infected plant material poses the greatest risk of the disease entering Australia.
Growers and home gardeners
- Only source planting material for citrus trees from suppliers who source their budwood from Auscitrus.
- Check your citrus plants for signs of cankers and other symptoms.
What to do
If you see scabby marks on citrus leaves and fruit or on related species:
- take a photo
- do not disturb infected plant material (this may be as simple as closing the doors on a shipping container or preventing access to an orchard)
- wash your clothes and boots.