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Plant diseases
Citrus canker
Xanthomonas citri subsp. citri · Bacterium
Also called Asiatic citrus canker (Australia).
Illustration
Raised, corky spots with yellow halos on citrus leaves, fruit and twigs. Australia and New Zealand are free of it, so if you think you've found it there, don't touch or move anything: photograph it and report it.
How to spot it
- Raised, corky, tan-to-brown spots with an oily, water-soaked edge.
- A yellow halo around each spot.
- Spots on both sides of the leaf, more raised underneath; older ones look like craters.
- Rough, corky scabs on fruit and twigs, and early fall of leaves and fruit.
Easily confused with
Citrus scab
Drier-looking spots with no yellow halo, and it distorts the leaves.
Citrus leafminer
Silvery, winding tunnels and curled leaves, but no raised corky spots (though canker can follow leafminer tunnels).
Where it's a problem
- Australia: Declared free in April 2021 after the Northern Territory outbreak. It's prohibited matter in Queensland and notifiable in NSW: report suspected cases to the Exotic Plant Pest Hotline, 1800 084 881.
- New Zealand: Not present, and must be reported (0800 80 99 66).
- USA: Established in Florida, which is under federal quarantine: don't move citrus fruit or plants out of quarantine areas.
- Europe: Absent, and a quarantine pest.
What to do
- In Australia and New Zealand, don't touch suspect spots or move any plant material off your property: photograph it and report it straight away.
- In US quarantine areas, don't send or carry home-grown citrus fruit or plants out of the area.
- Buy citrus trees only from registered, certified nurseries.
- Where it's established, windbreaks and leafminer control reduce its spread.
Where it's absent, the rule is report it, not treat it. Where it's established, copper sprays are used to protect young fruit.
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Sources
- Business Queensland: Asiatic citrus canker
- ACT Government: Citrus canker
- USDA APHIS: Citrus canker
- Florida Department of Agriculture: Citrus canker FAQ
- EPPO Global Database: Xanthomonas citri
- University of Florida IFAS: Citrus canker
Facts checked Sunday 27 September 2026. General guidance only: follow your local council, agency and product label.