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Blackleg
Pectobacterium atrosepticum
Bacterial diseaseHigh impact
A bacterial disease that causes the stem bases of potato plants to rot and blacken. Infected plants wilt, collapse, and die. Spread through contaminated seed tubers and by water movement in the soil.
Key facts
- Type
- Bacterial disease
- Affects
- Potato
- Active season
- May - Aug
- Peak season
- Jun - Jul
- Vulnerable stages
- Growing · Harvesting
- Spread rate
- moderate
- If confirmed
- Act now
Signs & symptoms
- -blackening and rotting of stems at or below soil level
- -plant wilting and yellowing before collapsing
- -soft, foul-smelling rot in the stem base and sometimes the seed tuber
- -plants pulling out of the soil easily with rotted roots
Management
Do now
- -Remove and bin infected plants including the seed tuber - do not compost
- -Do not water the surrounding area heavily as this spreads the bacteria
- -Mark affected plants and avoid reusing that area for potatoes without soil improvement
Prevention
- -Buy only certified disease-free seed potatoes
- -Rotate potatoes to fresh ground each year
- -Improve drainage in affected beds - waterlogging encourages spread
Further reading
- -Blackleg spreads most readily in wet seasons and waterlogged soil - good drainage significantly reduces risk
- -The disease typically originates in infected seed tubers; buying certified stock is the most reliable preventive measure
- -Neighbouring plants are rarely directly infected - blackleg tends to occur on individual plants