Gray mold on lettuce
Botrytis cinerea attacks lettuce at the base of the rosette and wherever it is damaged. Under cover it is the commonest reason plants collapse just before harvest, showing as a gray, dusty bloom.
Symptoms
- Watery, brown rot at the base of the rosette and the root collar
- A gray, dusty bloom of spores on the rotting tissue
- The whole rosette wilting even though the soil is moist
- Brown patches on the lower leaves that touch the soil
- The rosette parting easily from the root
What it does to the crop
- Plants collapsing right before harvest
- Heads rotting in transit and storage
- Losses running into tens of percent under cover
- Spores infecting further plants in the tunnel
What encourages it
- Humidity above 90%
- Temperature 15-20°C with poor ventilation
- Transplants set too deep
- Physical damage and leaf debris left in the crop
Prevention
- Plant shallowly, without burying the heart of the plant
- Ventilate the tunnel regularly, especially in the morning
- Drip-irrigate instead of watering overhead
- Remove infected plants and leaf debris from the crop
- Keep to the correct plant spacing
⚠️ 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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