What is Bacterial Soft Rot?
Bacterial soft rot is a destructive plant disease that causes plant tissues—particularly stems, roots, bulbs, and stored vegetables—to become mushy, foul-smelling, and water-soaked. It is caused by several species of bacteria, most commonly Pectobacterium and Erwinia, which break down plant cell walls and turn firm tissue into a soft, slimy mass.
This disease affects a wide range of plants, including potatoes, onions, carrots, lettuce, squash, tomatoes, houseplants, and many ornamentals. Soft rot is especially common in vegetables stored under warm, humid, or poorly ventilated conditions.
Life Cycle
Bacterial soft rot begins when bacteria enter plant tissue through wounds, insect damage, cracked skin, or natural openings. Once inside, they multiply rapidly, releasing enzymes that break down plant cells. In infected vegetables or bulbs, the rot can continue even after harvest.
The bacteria thrive in warm, wet conditions—typically between 70–90°F. They spread through splashing water, contaminated tools, insects, infected soil, and improperly cleaned storage areas. In the garden, wet soil and poor drainage make infections more likely.
Soft rot bacteria can persist in soil, plant debris, compost piles, and storage bins. They may survive winter in plant residue or in infected produce kept indoors, making sanitation essential for long-term control.
Symptoms
Early Stage
- Water-soaked, slightly soft spots on stems, roots, or produce
- Faint browning or discoloration around wounds
- A mild sour odor beginning to develop
- Leaves on affected stems may wilt or yellow
Middle Stage
- Rapidly expanding soft, mushy areas on plant tissue
- Clear or milky ooze from damaged stems or produce
- Strong foul smell as bacteria break down tissue
- Collapse of stems or plant bases
Late Stage
- Large portions of the plant turn into a slimy, wet mass
- Tissue detaches from the plant easily due to severe decay
- Complete rot of stored vegetables or bulbs
- Death of affected plants or unusable produce
How to Control Disease Progression
Once bacterial soft rot sets in, it progresses quickly. Immediate action can help limit the spread to nearby plants or stored produce.
- Remove and dispose of infected plants or produce immediately—do not compost them.
- Improve air circulation around plants, especially in humid environments.
- Reduce watering and avoid splashing water on plant stems or foliage.
- Increase soil drainage by amending heavy soils with compost.
- Clean contaminated tools, storage bins, and surfaces with a disinfectant.
- Keep vegetables stored in cool, dry, well-ventilated conditions.
Treatment Options
Because bacterial soft rot progresses rapidly and penetrates deeply into tissues, chemical treatments are generally ineffective. Management focuses on removing infected material and improving conditions to prevent further spread.
Organic Treatment Methods
- Improve soil structure with compost to promote good drainage.
- Use clean, sanitized tools when working with plants.
- Apply biological control products containing beneficial microbes if available locally, which may help suppress bacterial populations.
- Use mulch to reduce soil splashing onto stems and leaves.
Chemical Treatment Options
There are no chemical sprays that reliably cure bacterial soft rot in home gardens. Copper-based products may provide limited protection when used preventively, but they cannot stop an active infection.
Step-by-Step Treatment Procedure
- Identify and remove any infected plant parts or produce immediately.
- Sanitize tools with a 10% bleach solution or 70% alcohol.
- Improve soil drainage and reduce excess moisture around plants.
- Adjust watering practices to keep stems and foliage dry.
- Monitor nearby plants daily during warm, humid conditions.
Expected Timeline for Recovery
Plants with minor soft rot in early stages may recover once affected areas are removed and conditions improve. However, many cases—especially those affecting stems or stored produce—progress too quickly for recovery. Prevention is far more effective than treatment.
Prevention Strategies
- Plant in well-drained soil to prevent waterlogging.
- Avoid injuring plants during harvest, pruning, or cultivation.
- Harvest vegetables during dry weather and handle them gently.
- Store produce in a cool, dry, ventilated place.
- Do not wash produce before storage unless completely necessary; excess moisture encourages rot.
- Rotate crops to reduce bacteria buildup in soil.
- Sanitize tools, containers, and storage surfaces regularly.
- Use raised beds or mounds in areas prone to poor drainage.
