Bacterial canker / PSA (kiwi)
Dark angular leaf spots, reddish oozing cankers on canes and trunk, wilting shoots тАФ incurable once established, so clean material, tool hygiene and dry-weather pruning are the real defences.
- Pathogen
- Pseudomonas syringae pv. actinidiae (bacterium)
- Attacks
- Leaves, canes, trunk, shoots, blossom
- Favoured by
- Cool, wet weather; wounds; soft growth
- Best defence
- Certified clean vines, tool hygiene, dry pruning
Overview
Bacterial canker of kiwi, caused by Pseudomonas syringae pv. actinidiae (PSA), is the most serious disease of the crop worldwide and has devastated kiwi industries in several countries. It shows as dark, angular leaf spots often ringed with yellow, reddish or rusty ooze from cankers on the canes and trunk, wilting shoots, and in bad cases the death of whole vines тАФ a vine cannot recover once the trunk is badly cankered.
It spreads by rain, wind, pruning tools and, most importantly, on infected planting material, and is worst in cool, wet conditions. Because there is no cure once a vine is badly infected, control is overwhelmingly about prevention: planting only certified PSA-free vines, disinfecting tools between vines, pruning only in dry weather, avoiding soft nitrogen-pushed growth and overhead wetting, and removing infected material promptly. The related reddish "bleeding canker" and blossom-blight symptoms seen in cool wet springs are part of the same bacterial complex.
How to identify it
- Dark, angular spots on the leaves, often with a yellow halo.
- Reddish or rusty ooze from cankers on the canes and trunk ("bleeding canker").
- Wilting shoots and, in cool wet springs, rotting of flower buds and blossom.
- In bad cases, dieback and death of whole vines тАФ the trunk cannot recover once badly cankered.
The damage it does
- Kills canes and whole vines, destroying a long-term, high-value planting.
- No cure once a vine is badly infected тАФ it can only be contained and removed.
- Spreads rapidly through an orchard on tools, rain, wind and infected material.
When to act
- Act on prevention before planting тАФ source only certified PSA-free vines.
- Step up vigilance and copper sprays around bud break and through cool, wet spells.
- Remove and destroy infected canes the moment cankers appear, cutting well below the lesion.
Organic & cultural control
- Plant only certified PSA-free vines тАФ this is the single most important defence.
- Disinfect pruning tools between every vine, and prune only in dry weather.
- Avoid overhead wetting and excess nitrogen (soft growth is more susceptible).
- Cut out and destroy cankered canes well below the lesion, and remove severely infected vines.
Chemical control
- Protective copper sprays, especially around bud break, leaf fall and through cool wet weather.
- There is no curative chemical тАФ copper only protects healthy tissue, it does not cure an infected vine.
- Confirm the current copper programme and any restrictions with your local horticulture department/KVK.
Crops most at risk
Where this problem is called out in our crop guides тАФ open a crop for the full package of practices.
Frequently asked questions
Can a kiwi vine with bad bacterial canker be cured?
No. Once a vine is badly infected тАФ especially once the trunk is cankered тАФ there is no cure; copper sprays only protect healthy tissue, they do not clear an established infection. Cut out affected canes well below the lesion, and remove and destroy severely infected vines to protect the rest of the orchard. Everything in PSA management is about prevention and containment, not cure.
How do I keep PSA out of a new kiwi orchard?
Start with certified PSA-free planting material тАФ the disease most often arrives on infected vines. Then disinfect pruning tools between vines, prune only in dry weather, avoid overhead wetting and excess nitrogen, and apply protective copper sprays around bud break and through cool, wet spells. Clean material and hygiene keep PSA out far more reliably than any spray can control it once it is in.
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.