Sclerotinia shoot rot of grapevines in Western Australia

Page last updated: Tuesday, 14 May 2019 - 1:13pm

Sclerotinia shoot rot is caused by the fungus Sclerotinia sclerotiorum. It was recorded in WA vineyards many years ago but only appears sporadically when rainfall and cool weather occur in early spring. Little is known about the life cycle of the disease in vineyards.

Shoot rot can reduce yield by damaging or killing fruit-bearing shoots in the current season and, potentially, in future years. Research has indicated it can be controlled by application of fungicides.

Background

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 WA.

It has also affected grapevines in a number of the cooler growing regions of South Australia. Numerous vineyards in the south-west of Western Australia 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.

Symptoms

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).

Sclerotinia shoot rot infection of a grape vine showing as a pale brown lesion at the base of a shoot or a node
Figure 1a Sclerotinia shoot rot infection appears as a pale brown lesion either at the base of a shoot or a node
Second image of Sclerotinia shoot rot infection of a grape vine showing as a pale brown lesion at the base of a shoot or a node
Figure 1b Sclerotinia shoot rot infection appears as a pale brown lesion either at the base of a shoot or a node

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).

Grape shoot showing the white fungal growth which develops after moist, warm conditions
Figure 2 White fungal growth on the shoot after moist warm conditions
Black sclerote on the outside of the shoot. Sclerotes are the survival structures of Sclerotinia shoot rot
Figure 3 A black sclerote (centre, top), formed on the outside of the shoot. Sclerotes are the survival structures of Sclerotinia shoot rot

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.

Management

Sclerotinia shoot rot infection is slowed by warm dry conditions. If these occur in spring, the disease is unlikely to cause significant yield loss.