Sclerotinia rot on lettuce
Sclerotinia sclerotiorum causes sudden wilting and rotting of lettuce at the base of the rosette. The tell-tale signs are a white, cottony growth and black resting bodies that stay in the soil for years.
Symptoms
- The whole rosette wilting suddenly while the soil is moist
- White, cottony fungal growth at the base of the plant
- Hard, black sclerotia the size of a grain within the growth
- Watery, soft rot of the root collar
- The rosette parting easily from the root
What it does to the crop
- Total loss of the affected plants
- Plants collapsing in patches across the bed
- Soil contaminated with sclerotia for 5-8 years
- Later crops of susceptible vegetables becoming infected
What encourages it
- Cool, wet weather at 15-20°C
- Heavy, wet soils and a dense crop
- Growing after lettuce, beans, carrots or oilseed rape
- Crop debris left lying on the soil surface
Prevention
- Rotate with a 4-5 year break for susceptible crops
- Plant further apart and keep air moving through the crop
- Remove infected plants along with the sclerotia and a spadeful of soil
- Avoid overwatering
- Mulch to keep leaves off the soil
⚠️ 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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