Symptoms Usually the stalk rots just above soil level , causing the plant to wilt and ripen prematurely. Severely attacked plants can lodge. Affected tissues are usually a leached greyish white or brownish white. The stem can also be infected 30 to 45 centimetres or more above the soil surface. Cause Sclerotinia stem rot is caused by the fungus Sclerotinia sclerotiorum .
Sclerotinia can survive as sclerotia in the soil for many years.
The fungus probably also survives in the soil by colonising the roots of other plant species. During cool moist weather sclerotia near the surface germinate and produce small, cream, mushroom-like bodies called apothecia, containing many ascospores. These are carried by the wind to nearby crops. Normally the spore must first germinate on, then infect, dead or dying plant material such as dead leaves or fallen flower petals caught in leaf axils. Then it invades healthy tissues.