Sclerotinia disease is caused by the fungus Sclerotinia sclerotiorum. This fungus produces black, seed-like structures (sclerotia) which can live for long periods in the soil and cause disease in a very wide range of plants. Damage is seen in summer and early autumn.
S. sclerotiorum attacks a wide range of plants including vegetables: lettuce, beans, celery, chicory, cucumbers, tomatoes and peas; and many ornamentals, especially plants with hollow stems such as Delphinium, Dahlia and Helianthus (sunflower) and related yellow daisies.
In commercial agriculture and horticulture S. sclerotiorum is a major problem in lettuce, oilseed rape and sunflower production.
Other very similar Sclerotinia species attack gladioli (S. gladioli) and bulbs (S. bulborum). In addition to S. sclerotiorum, lettuce can also be affected by S. minor.