Sclerotinia disease is a fungal infection of many vegetables and ornamental plants. The fungus lives for long periods in the soil. When infected, plants rot at the base and a white fluffy mould may grow on affected parts.
What is sclerotinia disease?
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.
When plants infected with sclerotinia die, the black sclerotia fall to the soil, where they can remain viable for several years. It is these sclerotia that spread the disease. They can infect plants in two ways:
- Winter chilling followed by rising temperatures stimulate sclerotia to germinate and produce a structure called an apothecium, which looks like a small brown cup. This releases airborne spores which will land on leaves, and cause infection if that plant is susceptible. These spores require wet conditions to infect, so infections are more common in wet weather
- Less frequently, the sclerotia germinate in the soil and infect plants directly. Fungal threads (hyphae) grow out from the sclerotium and through the soil, coming into contact with the base of the plant. This is especially likely when plants are crowded and the fungus only has to grow a short distance to encounter one. This is the same type of infection process that occurs in onion white rot
There is no secondary spread by spores produced on the first infections, unlike with other diseases such as rusts and powdery mildews. However, each apothecium can produce many thousands of spores, and if weather conditions are suitable outbreaks can be serious, especially in commercial crops.