Citrus canker
Raised, corky, brown scab-like lesions ringed by a yellow halo on leaves, twigs and fruit — a wind-and-rain-spread bacterial disease.
- Pathogen
- Bacterium (Xanthomonas citri)
- Spreads by
- Wind-driven rain, splash & tools; wounds
- Favoured by
- Warm, wet, windy weather; tender flush
- Main risk
- Blemished fruit, leaf & fruit drop, dieback
Overview
Citrus canker is a bacterial disease (Xanthomonas citri) that affects most citrus, and is especially severe on acid lime, lemon and grapefruit. It produces raised, rough, corky, brown scab-like lesions, typically surrounded by a yellow halo and often with a water-soaked margin, on the leaves, twigs and fruit. On leaves the spots appear on both surfaces; on fruit they are corky raised cankers that disfigure the fruit and cut its market value.
A severe attack causes leaf spotting and drop, twig dieback, and premature fruit drop or blemished fruit. The bacterium spreads by wind-driven rain, splashing, and on tools, and enters through natural openings and wounds — including the feeding wounds of the citrus leaf miner, which greatly worsens canker. It is favoured by warm, wet, windy weather and by young, tender flush. Because there is no cure once tissue is infected, control combines clean planting material, pruning and sanitation, protective copper sprays timed to the new flush, and leaf-miner management.
How to identify it
- Raised, rough, corky, brown scab-like lesions with a yellow halo, often with a water-soaked margin.
- Spots on both leaf surfaces, on twigs, and as corky raised cankers on the fruit.
- Leaf spotting and drop, twig dieback, and premature or blemished fruit that loses market value.
- Worse on young, tender flush and where citrus leaf miner tunnels have opened the tissue.
What causes it and when
- The bacterium Xanthomonas citri, spread by wind-driven rain, splashing water and on tools and hands.
- Enters through natural openings and wounds — including the feeding wounds of the citrus leaf miner, which greatly increases canker.
- Favoured by warm, wet, windy weather and by flushes of young, tender growth.
- Carries over on infected leaves, twigs and lesions on the tree and in debris.
Cultural & organic control
- Plant only disease-free, certified nursery plants and grow tolerant varieties/rootstocks where available.
- Prune out and destroy cankered twigs and leaves in the dry season, and remove fallen infected debris.
- Provide windbreaks to cut wind-driven rain spread, and avoid working the trees when wet.
- Disinfect pruning tools, and manage the citrus leaf miner whose wounds worsen canker.
Chemical control
- Spray protective copper-based bactericides (e.g. copper oxychloride) timed to protect each new flush and developing fruit, especially before wet, windy spells.
- Combine copper sprays with citrus leaf miner management, since its tunnels open the way for the bacterium.
- Repeat as recommended through the flushing/fruiting period and observe safety intervals.
- Confirm the current copper schedule and leaf-miner management for your area with your local KVK.
Prevent it coming back
- Start with clean planting material and tolerant varieties/rootstocks, and use windbreaks.
- Prune and sanitise in the dry season, disinfect tools, and remove infected debris.
- Protect each new flush with copper and manage the citrus leaf miner to deny the bacterium entry wounds.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My citrus leaves and fruit have raised corky brown spots with a yellow ring. What is it?
Those raised, rough, corky brown scab-like lesions with a yellow halo on leaves, twigs and fruit are citrus canker, a bacterial disease. It disfigures the fruit, drops leaves and kills twigs, and spreads in warm, wet, windy weather. There is no cure for infected tissue, so prune and destroy cankered parts, protect each new flush with copper sprays, manage the citrus leaf miner, and start with clean planting material.
Why does the citrus leaf miner make canker worse?
Because the leaf miner tunnels just under the leaf surface and leaves open feeding wounds, and the canker bacterium enters readily through exactly those wounds. Where leaf miner is active on the tender flush, canker infection and severity rise sharply. That is why control pairs copper sprays for the bacterium with leaf-miner management — protecting the flush from the miner also protects it from canker.
Can I cure citrus canker with a spray?
No — copper sprays are protective, not curative: they shield healthy tissue and new flush from infection, but they cannot heal a lesion that has already formed. So cankered twigs and leaves should be pruned out and destroyed, and copper applied to protect the new growth and fruit before wet, windy weather. Combine this with clean planting material, sanitation, windbreaks and leaf-miner management for real control.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.