Blackleg on potato
A bacterial disease (Pectobacterium atrosepticum, Dickeya solani) moving from the seed tuber into the stem. The stem base blackens and rots, and the plant yellows and dies. The same bacteria cause soft rot of tubers in store.
Symptom photos
Symptoms
- Black, slimy rot at the base of the stem
- Leaves yellowing, rolling upwards and stiffening
- Individual plants wilting and dying among healthy ones
- The stem pulls easily out of the clump, rotten base and all
- Wet tuber rot with an unpleasant smell
What it does to the crop
- Plants lost and gaps left in the crop
- Storage losses from soft rot of the tubers
- No effective control once symptoms appear
- Bacteria carried over on seed tubers into the next season
What encourages it
- Wet soil and temperatures above 20°C
- Seed tubers damaged when cut or planted
- Compacted, waterlogged sites where water stands
- Lifting tubers wet and storing them without ventilation
Prevention
- Plant healthy, certified seed potatoes
- Avoid cutting seed tubers and causing physical damage
- Grow on free-draining soil with no standing water
- Remove infected plants together with the mother tuber
- Dry tubers before storing and keep them well ventilated
⚠️ Before you reach for a spray
This atlas is informational and still growing — different diseases can look almost identical. Confirm the diagnosis and read the product label before applying any plant protection product. If you are unsure, ask your local extension or advisory service.
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