Sclerotinia shoot rot of grapevines is caused by the fungus Sclerotinia sclerotiorum. It was first detected on grapevines in the Swan Valley in 1988 but has since been found in most growing regions of Western Australia.
It has also affected grapevines in a number of the cooler growing regions of South Australia. Numerous vineyards in the south-west of WA reported sclerotinia shoot rot during the 2013/14 season.
It can cause yield loss and, in severe cases, death of shoots and arms (cordon). Little is known about the disease life cycle in vineyards but its appearance is associated with rainfall and cooler temperatures during the early part of the growing season.
S. sclerotiorum has a wide host range, infecting a number of commercially important vegetable and horticultural crops. Grape and Wine Research and Development Corporation (Wine Australia) funded research on the disease and its control and a report has been produced by the South Australia Research and Development Institute.
Shoot rot appears as a pale brown lesion on the shoot and develops either at the base of the shoot or at one of the nodes (Figures 1a and 1b).
Infection travels down the stem, girdling the shoot and making it break easily when bunches begin to develop or during windy conditions. If warm humid conditions occur after infection, a white fungal growth may appear from the lesion or sclerotes will form inside the shoot or on the outside of the wood (Figures 2 and 3).
Sclerotes are hard, black survival structures that fall from the infected shoot and remain viable in the soil or vine bark. Research in South Australia has indicated that several shoots on one arm can be infected at one time and the disease can travel into the arm which may die as a result, reducing yields for several years while new wood is established.
Despite being predominantly a shoot rot, S. sclerotiorum can infect berries. Berry infection is rare in the field and may occur after the berries are initially wounded.
Can be confused with?
Sclerotinia shoot rot can be visually indistinguishable from Botrytis shoot infection in the early stages of infection. The presence of sclerotia in or on the shoots, or white fungal growth, distinguishes it from the grey fungal growth of Botrytis cinerea. If you are unsure what is causing your shoot rot, send samples for diagnosis.
Sclerotinia shoot rot infection is slowed by warm dry conditions. If these occur in spring, the disease is unlikely to cause significant yield loss.