Eutypa dieback: prohibited disease

Background

Eutypa dieback caused by the fungus Eutypa lata is a major trunk disease of grapevines that reduces yields and causes a gradual decline in the productivity of the vine until its eventual death. It is not known to occur in Western Australia but is present in other grape growing regions of Australia and overseas.

The disease is particularly severe in cool climate regions with vineyards that have vines eight years or older. The fungus produces a toxin that stunts and distorts vine growth, including bunches.

The South Australian Research and Development Institute (SARDI) has conducted long-term scientific investigations into Eutypa dieback on grapevines and produced many publications on the disease.

Hosts

The causal fungus, Eutypa lata, has been reported to infect 88 different host plants including Vitis vinifera (grape). Other host plants include commercial horticultural crops such as stone fruit, pome fruit, citrus, fig and olive. Apricot trees are particularly susceptible with it causing gummosis symptoms. Susceptible ornamental species include oak and poplar trees.

Distribution

The known distribution of Eutypa dieback in eastern Australia has expanded in recent times as further surveys have been conducted. The disease has been found in South Australia, Victoria, New South Wales and Tasmanian growing regions.

Viticultural regions of the Adelaide Hills, Barossa, McLaren Vale, Riverland, Coonawarra, Central Ranges, Southern NSW, Tamar Valley, Coal River Valley and Derwent Valley have all reported the disease.

Symptoms

The incubation period occurs from the time of infection until visual foliage symptoms appear on the vine and this can be anywhere from one to eight years. Foliar symptoms can also vary from season to season as well.

Characteristic symptoms include stunted or distorted shoots that are often yellow and cupped with necrotic margins (Figures 1, 2 and 3). The disease may initially only affect one shoot on a grapevine, eventually spreading to multiple shoots. As the disease moves further down the trunk the entire arm can be killed followed by the trunk and eventually the vine.

Figure 1 An infected arm showing stunted shoot growth

Figure 2 Eutypa lata-infected shoots (circled) showing cupped leaves and necrotic (dead) margins

Figure 3 Infected shoots (circled) showing cupped leaves and necrotic (dead) margins

Bunches on infected shoots are smaller than uninfected shoots and fail to ripen.

Internally the fungus itself is slow growing. It invades through open wounds of the vine and as it progresses towards the roots it kills the internal tissue. This is characterised by internal wedge-shaped lesions of dead tissue when shoots or arms are viewed in transect at pruning time (Figure 4).

Figure 4 Internal wedge-shaped lesions can be a symptom of Eutypa lata or Botryosphaeria infection (see Can be confused with)

Externally the disease produces fruiting bodies on the wood of the vine (arms, trunk) that are revealed when the bark of the vine is removed. The mass of fruiting bodies appears as a charcoal coloured area on the vine (Figure 5).

It can take up to eight years after the initial infection before the development of the fruiting bodies.

Figure 5 Charcoal region of infected grapevine wood when bark is removed. Note the spore bodies protruding from the bark (white arrows).

When am I likely to see it?

Foliar symptoms of the disease are most obvious in spring when the shoots are about 30cm long. This allows comparison of stunted infected shoot growth with surrounding healthy shoots. As the season progresses it gets harder to see foliar symptoms as the healthy shoots and vines obscure the infected areas (Figures 2 and 3).

The wedge shaped internal lesions are most obvious during pruning.

Can be confused with

Eutypa dieback is difficult to distinguish from Botryosphaeria dieback which is present in the grape growing regions of WA. Botryosphaeria dieback symptoms include dead or dying arms (Figures 6 and 7) and wedged-shaped internal lesions (Figure 4).

Figure 6 Botryosphaeria dieback can kill arms or constrict spring growth; note no foliage symptoms except reduced growth

Figure 7 Botryosphaeria dieback can kill arms or constrict spring growth

As Botryosphaeria species do not produce a toxin they do not exhibit the foliar symptoms of E. lata. Botryosphaeria species are faster growing and symptoms are likely to appear on younger vines whereas E. lata is more often associated with mature, older vines.

Sending samples to a diagnostic laboratory can differentiate the two different fungal species.

Spread

Spores of E. lata are released after rainfall (>2mm) from the fruiting bodies on the wood (charcoal areas) and can travel in the wind for kilometres. The fungus invades fresh pruning cuts or wounds and slowly moves through the vine. Pruning wounds can remain susceptible up to four weeks after the cut if no treatments are applied to them and wound healing is slow.

Vineyards where old orchards, particularly apricot orchards are located nearby, are at higher risk of infection if the disease was present there prior to establishment of the vineyard.

What to do if I suspect I have it?

Eutypa lata is a prohibited organism for Western Australia. It is important that suspect infestations are reported. Please contact the Pest and Disease Information Service (PaDIS) to report this pest on 1800 084 881 or email info@agric.wa.gov.au.