Bottom rot on lettuce
Caused by Rhizoctonia solani, attacking the lower leaves that lie against the soil. It works up the rosette from below, producing a rusty-brown, dry rot with no dusty bloom.
Symptoms
- Rusty-brown, sunken patches on lower leaves and leaf stalks
- Rot starting on the leaves that touch the soil
- Brown, dry rot at the base of the rosette
- Brown fungal growth with no dusty bloom of spores
- The rosette dying back progressively from the bottom
What it does to the crop
- Lower leaves lost and heads needing heavy trimming
- Whole rosettes rotting before harvest
- Young transplants collapsing
- The fungus persisting in the soil and in crop debris
What encourages it
- Wet soil and warm weather at 18-25°C
- Planting too deep, letting leaves touch the soil
- A dense crop with moisture lingering at ground level
- Growing lettuce as a monoculture
Prevention
- Plant shallowly, on slightly raised ridges
- Mulch to keep leaves off the soil
- Drip-irrigate and avoid overhead watering
- Rotate crops and clear crop debris
- Keep good soil structure with no standing water
⚠️ 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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