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Trevor Wicks and Kent Davies
South Australian Research & Development Institute, C/- The Plant Research Centre, Hartley Grove, Urrbrae, SA 5064.
Published in Grape Grower & Winemaker, Annual Technical Issue 1999

Summary

Eutypa infection reduced bunch numbers in Shiraz from around 150 bunches per vine in healthy vines to less than 50 per vine in severely affected vines. Yield losses ranged from 0.6 Kg to 9 Kg/vine for mildly and severely affected vines respectively. In vineyards with an average of 30.8% of vines infected, yield losses of at least 860 Kg/Ha can be expected for Shiraz and 740 Kg/Ha for Cabernet sauvignon.

In a Shiraz vineyard where at least 47% of vines were infected with Eutypa, yield losses of 1500 Kg/Ha were estimated to cost over $2,800/Ha.

The costs of reduced wine quality due to uneven berry maturity from infected vines as well as the costs associated with vine removal, replanting or reworking and the loss of productivity also need to be considered in addition to the direct yield loss attributed to Eutypa.

Overall these results show yield was significantly reduced in vineyards infected with Eutypa.

Background

Eutypa dieback, caused by the fungus Eutypa lata is a lethal disease of grape vines. The fungus enter through large pruning wounds, grows slowly in the woody tissue and eventually kills the vine (Carter 1991).

Surveys on the incidence of this disease have shown that Eutypa dieback is widespread in South Australian vineyards, occurring in all grape growing areas. Also within any district the disease was more prevalent in Shiraz and Cabernet sauvignon than in other cultivars (Highet and Wicks 1998). However this survey and others (Wicks 1975) recorded only the presence and absence of the disease on a vine and did not document the severity of the infection.

Vineyard managers are aware of the loss this disease causes in established vineyards, but due to the yearly variation in yield it is difficult to quantify the effect of this disease on vineyard productivity.

Except for work conducted in California, few detailed studies on the effect of Eutypa on grape vine yield have been conducted. The California studies (Monkvold et al 1994) estimated that yield reductions ranged from 30% to 62% in vineyards depending on the severity of the disease.

Whether similar yield reduction are occurring in Australian vineyards is unknown. However this information is essential for vineyard managers to make decisions as to whether to replant, rework, or retrain affected vines and at what stage of the disease development these operation need to be undertaken.

A study was conducted to obtain data on the effect of Eutypa infection on vineyard productivity and to extrapolate this information to determine the impact of this disease on the grape industry.

Materials and methods

Vines infected with Eutypa show typical stunted shoot symptoms particularly around flowering. At this stage the level of infection was rated on a 0 to 4 scale of shoot stunting as indicated in the previous report (Wicks and Highet 1998) where 1 = mild symptoms of marginal leaf necrosis to 4 where the shoots were severely stunted and spindly with few to no leaves. The percentage of the foliage showing the stunted shoot symptoms was rated and the severity calculated as "Infection rating x percent foliage infected", such that healthy vines rated 0, and vines with all shoots severely stunted rated a maximum of 400 (100% x 4).

Isolations from vines with stunted shoots were not undertaken as previous experience (Wicks unpublished and Munkvold et al 1984) consistently show that these vines are infected with Eutypa lata. In addition the symptoms of Eutypa infection are very distinctive and no other grape vine disease recorded in Australia causes symptoms that could be confused with those caused by Eutypa. In most infected vines not all shoots are stunted and often only one cordon is infected.

A detailed survey of 5 Shiraz vineyards in the Eden Valley was undertaken with the incidence and severity being recorded in at least 500 vines per vineyard.

This data was used to estimate the incidence and severity of vines showing Eutypa symptoms throughout the region. Bunch number and yield per vine was recorded on at least 100 vines with varying levels of Eutypa infection in a Shiraz and Cabernet sauvignon vineyard in the Eden Valley region. Similar disease assessments were made on two vineyards in the McLaren Vale area with the intention of obtaining bunch numbers and yield per vine. Unfortunately these vineyards were harvested before individual vine yields could be recorded.

Results

The survey of 5 vineyards in the Eden Valley showed that 30.8% of vines in the area displayed symptoms of Eutypa infection and ranged from 24% to 47% of vines infected (Table 1a).

A more detailed breakdown on the severity of the Eutypa infection in the vineyards showed that an average of 6.6% of vines were severely infected and that in the vineyard with the highest incidence 16% of vines were severely infected (Table 1b).

When vine yield is plotted against Eutypa severity it is obvious that yield is significantly affected by Eutypa. In fact yield of Shiraz vines is reduced from around 10 Kg per vine in healthy vines to around 2.5 Kg per vine in vines severely affected by Eutypa.

Similar trends are shown with bunch numbers where around 150 bunches per vine were recorded in healthy Shiraz vines and less than 50 in vines with severe Eutypa infection. More severe yield reductions were detected in Cabernet sauvignon where no yield was obtained from vines with a severity rating of more than 250.

The expected yield loss in Shiraz was estimated by taking the mid point of each severity range, determining the number of vines in each category (from a basis of 1670 vines/Ha) and calculating the expected loss from the regression. The data shows that in a vineyard with 30.8% Eutypa infection a loss of at least 860 Kg/Ha can be expected.

Discussion

Bunch weights from individual vines assessed for the incidence and severity of Eutypa showed that Eutypa is causing significant yield reductions in the Eden Valley. For example in vineyards where Eutypa symptoms were detected in 30% of vines, a yield reduction of at least 860 Kg/Ha was estimated. At a cost of $1350/tonne this amounts to a direct loss of over $1000/Ha. In vineyards where the value of the grapes is higher than this, Eutypa is causing substantial losses. Losses in Cabernet sauvignon vineyards with the same incidence of Eutypa were estimated to be similar although slightly less than that of the Shiraz vineyards.

Vineyards with Eutypa infections in 50% or more of the vines are not uncommon in many grape growing areas of South Australia and in these vineyards yield losses are likely to be more than 1500 Kg/Ha.

Not considered in this survey were the additional costs of Eutypa infection as a result of reduced wine quality due to the uneven berry maturity from infected vines. Other losses also associated with Eutypa are the inefficient use of irrigation, fertiliser and pesticides applied to declining vines and also the cost of removing or reworking severely affected vines and the losses associated with the production from the young vines.

The yield reductions found in this limited survey were similar to that reported from California where reduction for whole vineyard production ranged from 30% to 62%.

Although this data was collected from two vineyards it is the first detailed study on the effect of Eutypa on grape vine yield in Australia and as such shows that Eutypa is significantly reducing yields in many vineyards.

Several questions remain unanswered and further work needs to be done. For example detailed work on yield and disease severity in several grape varieties and grape growing districts needs to be undertaken to determine at what stage of Eutypa infection does a vine become uneconomic and at what level of vineyard infection should reworking or replanting be undertaken.

Acknowledgement

We thank the Phylloxera Board of South Australia for contributing funds towards this study.

References

Carter, M.V. (1991) The status of Eutypa lata as a pathogen. Monograph - Phytopathological Paper No. 32 issued by the International Mycological Institute.

Highet, A. and Wicks, T. (1998) The incidence of Eutypa dieback in South Australian vineyards. Annual Technical Issue - 1998. The Australian Grape Grower and Winemaker. 414: 135-136.

Munkvold, G.P., Duthie, J.A. and Marois, J.J. (1994) Reduction in yield and vegetative growth of grape vines due to Eutypa dieback. Phytopathology 84: 186-192.

Wicks, T. (1975) The dying arm disorder of vines in South Australia. Agricultural Record. 2: 14-20.

Table 1a and b.  Incidence (a) and severity (b) of Eutypa in Shiraz vines in the Eden Valley - South Australia - November 1998