Sclerotinia stem rot is a fungal disease that causes stem and plant death during flowering.
What to look for
Paddock
Bleached or light brown dead plants among green healthy plants after flowering.
Plant
Light brown watery discoloured patches on stems, branches and pods that expand and take on a greyish-white colour.
Lesions girdle the stem causing parts above the lesion to die.
Hard black bodies called sclerotia are found inside an infected stem when it is split open.
Plants die prematurely, and often lodge.
In wet or humid weather, a white growth resembling cotton wool can develop on lesions that may also contain sclerotia.
Infected pods appear creamish-white in colour and usually contain white mouldy seeds.
Where did it come from?
Contaminated soil
Sclerotinia can survive as sclerotia (hard, dark resting bodies) in the soil for many years, and infects plants, such as broadleaf crops, wild radish and capeweed.
Lupins and chickpeas are commonly infected whereas faba beans and field peas appear to be less susceptible.
During cool moist weather sclerotia near the surface germinate and produce small, cream, mushroom-like bodies containing many spores. 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 flower petals) before it invades healthy tissues.
Infected petals that lodge between the stems and leaves are a major infection source. Cool, wet weather favours the disease and mists, dews and fogs provide enough moisture for infection.
Less commonly, sclerotes directly infect the stem at the surface causing a collar rot that kills the plant.
Management strategies
Spraying fungicide
Cultivation
Fungicide spray at either 15–30 or 50 per cent bloom may give excellent control of the disease, and is most likely to be economic when:
Sclerotinia is present in the paddock, or adjacent paddock in the last 3 years.
Canola or susceptible crops has been grown in the past two years.
Persistent wet weather at flowering
Mouldboard ploughing is effective in burying sclerotia provided that it is not repeated within 5 years.
