Bacterial soft rot: how to recognise and treat it

Disease

Symptoms

Small water-soaked spots that quickly enlarge, sink and turn soft and mushy; the tissue underneath is cream to black.
Slimy ooze and a strong, foul smell from the rotting tissue.
Whole roots, tubers, bulbs, heads or fruit can collapse within a few days, often leaving only the skin — in the garden and in storage.
Potato stems may turn black and rot from the base upwards (blackleg).

Once a plant is infected there is no cure — remove and discard infected plants or parts at once; do not bury or compost them.
Wash your hands after handling rotted plants, and disinfect tools for at least 30 seconds in 10 % household bleach or 70 % alcohol.
Sort stored produce and remove any rotting pieces straight away; separating stored roots with layers of dry straw or sand slows the spread.

No chemical treatment cures soft rot; rely on hygiene, dry conditions and avoiding wounds.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Grow in well-drained soil, water evenly but not too much, avoid overhead watering and do not crowd plants.
Avoid wounding plants when weeding and harvesting, control insects that wound them (such as cabbage root fly), and keep soil calcium adequate.
Harvest in dry weather, cure crops that need it, store only sound produce in a cool, dry, well-aired place.
Where soft rot recurs, do not grow susceptible crops there for at least 3 years — sweet corn is a good alternative; clear plant debris at the end of the season.

Figures checked against these sources.