Sclerotinia stem rot
Sclerotinia stem rot (Sclerotinia sclerotiorum) is a fungal disease which infects most broad leaf crop and pasture species but not cereals. It is most common in higher rainfall areas and usually affects plants after flowering in warm and damp conditions. Outbreaks of the disease are sporadic dependent on paddock history and seasonal weather conditions, often the disease affects only a percentage of the crop and the loss of yield is proportional to area infected. Crops with lush dense canopies in seasons with regular rainfall are at greatest risk, particularly when sown on paddocks with a history of sclerotinia infection in canola or lupins previously. In severe cases sclerotia become mixed with harvested seed which may incur extra cost of grading seed to remove them.
Predominantly lesions occur in the upper half of the main stem or branches and on flowers and pods. The fungus produces a white cottony-looking growth that girdles the stem, causing the plant parts above the lesion to wilt and die. Infected pods can be completely covered by this white fungal growth. Hard black sclerotia, 2-8 millimetres (mm) in diameter, are produced in the fungal growth or in the cavities of infected stems or pods. Sclerotia can survive in soil for several years and are the source of new infections.
- Crop rotation can have some effect, although sclerotia survive for significant periods. Cereals are non-hosts and provide the most effective disease break.
- Avoid sowing lupins in close rotation with other broad leaf crop species, particularly canola.