Coonawarra Vine Health Project

Martin Wirper

Final Report

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Executive Summary

This report summarises the data obtained by the vine health project undertaken in 2012. Coonawarra

Cabernet Sauvignon blocks from across the region were assessed for the pests and diseases that have

been implicated in vine decline. Particular focus was placed on Phomopsis, Eutypa, vine scale and bud

mite. Measurements of unproductive cordon were made to provide data for potential production loss.

Disease diagnosis of unproductive cordon samples was conducted by the Horticultural Disease Diagnosis

service of SARDI.

Key findings from the project were that on average 18% of vine cordon in 2012 was not producing green

shoots. This percentage was higher for vines planted pre 1991 (designated “old”) and less for vines

planted from 1991 onwards (designated as “young”). Whether a block was severely frosted in 2006 had

little bearing on amount of unproductive cordon. Phomopsis symptoms were more prevalent than

Eutypa in “young” vines while the converse was true for “old” vines. Vine scale and bud mite are not

significant contributors to vine health. The number of green growing shoots did not correlate with

amount of unproductive cordon or vine age.

Conclusions that can be drawn are that vine age is better correlated with unproductive cordon than a

severe frost event. Phomopsis symptoms were more highly prevalent than Eutypa on green tissue, older

wood and infecting unproductive cordon of “young” vines. Disease diagnosis confirmed that the

pathogens Eutypa, Botryosphaeria and Phomopsis were present in unproductive cordon. Inherent vine

health is not in decline as vine age did not correlate with the mean number of shoots counted.

The data obtained in this project supports current research into grapevine trunk disease. As vines age

they are more likely to be infected by a combination of trunk diseases. As data was only collected for

one year no management recommendations have not been made. The data available can be used for

further surveys and to inform any vineyard management decisions.

Author

Martin Wirper is Assistant Vineyard Manager – Coonawarra North for Treasury Wine Estates. He has

held the role since 2006, prior to which he was Regional Viticulturist for Orlando Wines at Padthaway.

Martin is the second recipient of the Cabernet Leaders Award – originally funded by the Coonawarra

Grapegrowers Association (now the Coonawarra Grape and Wine Incorporated). This report is the

outcome of the scholarship awarded in 2013.

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Introduction

The primary aim of this project was to identify pests and diseases that could cause economic and quality

loss in Coonawarra vineyards. The secondary aim of the project was to provide additional data to

quantify the trunk disease issue in Coonawarra vineyards.

Materials and Methods

A one metre piece of PVC pipe with ten centimetre markings was used to assess levels of disease,

estimate bare or dead cordon, and count shoots. This is illustrated in Figure 1. All shoots in the one

metre segment were counted and then individually examined for the incidence of Phomopsis, Eutypa,

mite damage and scale.

Experimental protocol

Expressions of interest were sent out to Coonawarra Grape Grower members. For each business that

responded, between one and six Cabernet Sauvignon blocks were selected in consultation with vineyard

managers. A total of forty one blocks of varying age and management type were assessed.

Experimental design

The standard method was to choose sites randomly from four vineyard rows spread across each block.

Along each row, three sites on the left hand side of the row and three sites along the right hand side

were monitored. Monitoring was conducted from the 25th of October 2012 until the 20th of December

2012.

Data collection

Vineyard age, clone and rootstock type were recorded prior to monitoring. In addition, it was recorded

whether blocks had been significantly frosted in 2006. A block was deemed to have been significantly

frosted if economic crop loss occurred.

A length of vine arm was identified as ‘dead’ if there was no growth from the end of the arm back

towards the vine trunk. A length of vine arm was identified as ‘bare’ if there were no green shoots at the

typical spacing for the monitored block. Typical bare arm symptoms are shown in Figure 2. The

measurements for bare and dead arm were added together and termed unproductive.

A separate estimate was made of areas of bare wire (due to missing arms or whole vines).

Samples for disease diagnosis were taken in September 2014. Rows that had been assessed with

significant sections of dead wood were selected for sampling. Samples were analyzed by the SARDI

horticultural diagnostic survey.

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Figure 1 Vine monitoring showing healthy, uninfected vines.

Figure 2 Typical bare arm symptoms; healthy vegetative growth either side of bare area.

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Results and Discussion

For all blocks assessed the average year of planting was 1990. As such, blocks planted in 1990 or earlier

were designated as ‘old’, while blocks planted from 1991 onwards designated ‘young’. This distinction

was made to determine if there is any effect of vine age on the health of the vine.

A total of 1,038 segments, or approximately 1 kilometre of vineyard cordon, was assessed. A total of

26,584 shoots were counted. This is an average of 25.6 shoots per metre for Coonawarra Cabernet

Sauvignon.

A total of 137.35 metres was assessed as being bare, and 49.95 metres as dead. This is a total of 187.3

metres or 18% of the vine row being assessed as bare or dead arm; or unproductive cordon. Areas of

cordon that are bare are not necessarily dead, and live wood can be found without Eutypa symptoms as

shown in Figure 3. This figure shows old, live wood lacking one year old shoots that has been cut from an

area of bare arm.

Figure 4 shows live wood at the base of the spur. Such black discolouration has been attributed to

Phaeomoniella chlamydospora – the causal agent of Petri disease and Esca, however, disease testing of

black flecks such as these failed to find any pathogens.

Figure 3 Spur of live wood from area of cordon designated as bare.

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Figure 4 Cross section of live wood taken from area of bare arm.

Of the vines designated as young; 15% in total was unproductive cordon. Of the vines designated as old; 21% was unproductive. However, the average number of shoots in vineyards designated as ‘young’ was 26.35, and 26.04 in those designated as ‘old’. Confidence intervals at 95% are 0.038 and 0.031 respectively.

The actual average shoot density (excluding bare or unproductive arms) is 31 shoots per metre. This includes mite-damaged shoots, which in some cases were severely affected and unlikely to develop to maturity.

The metres of unproductive cordon in a block compared to the shoot count are shown in Figure 5. This shows there is no correlation between the amount of unproductive cordon and number of shoots.

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Figure 5 Metres of unproductive cordon versus total shoots by block.

From the estimate of bare wire, approximately 1% of wire is not filled with cordon in Coonawarra Cabernet vineyards. This makes the total length of unproductive vineyard row - on average across Coonawarra, 19%. The majority of this is ‘bare’ or ‘dead’ arms - as opposed to missing cordons or vines.

Pests and Diseases

Out of 1,038 monitoring sites, 19% had symptoms of Eutypa infection evident in the foliage. However, of the total shoots counted, only 3% exhibited Eutypa symptoms. That is to say, one vine in five had some foliage symptoms of Eutypa. On average, 3% of all Cabernet Sauvignon shoots had Eutypa symptoms. Typical symptoms are shown in Figures 6 and 7.

In a study by Sosnowski et al. (2007), three Coonawarra blocks showed an incidence of 20-80% over the years 1999 – 2002. In that study, only three blocks were assessed for Eutypa and the purpose was to identify climate factors on Eutypa expression.

Two trials in the Adelaide Hills during 1996 to 1998 were assessed for incidence of Eutypa as part of a disease control trial (Sosnowski et al 2011). Incidence of Eutypa symptoms were 89% and 35%, however only 36 and 140 vines respectively were surveyed rather than a survey across the block.

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Metres unproductive cordon vs total shoots

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Figure 6 Eutypa showing stunting.

Figure 7 Eutypa symptoms with characteristic wedge-shaped dead wood

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Figure 8 shows a cross section of a spur with dead heartwood. The shoots arising from this spur had Eutypa-like symptoms, whereas the wood lacks the distinctive wedge-shaped discolouration. It is likely that some of the stunted shoots that are being ascribed to Eutypa may be caused by Esca. However, disease diagnosis has not found the causal agent of Esca symptoms.

Figure 8 Severe stunting of shoots – old wood showing dead heartwood.

Phomopsis symptoms were observed in 68% of all sites, with a total of 11% of shoots being infected. To

be positively identified as Phomopsis shoots needed to have scarring as well as leaf spot symptoms.

Typical Phomopsis symptoms are shown in Figures 9 and 10.

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Figure 9 Typical Phomopsis symptoms

Figure 10 Close up of Phomopsis scarring.

In blocks designated as ‘old’, 4.25% of shoots monitored exhibited Eutypa symptoms, and 9.25% exhibited symptoms of Phomopsis. In blocks designated as ‘young’, 1.69% of shoots monitored exhibited Eutypa symptoms, and 11.58% exhibited symptoms of Phomopsis.

For each monitored block metres of unproductive cordon was compared to observed Eutypa symptoms and Phomopsis symptoms. No correlation between areas of bare wire severity of Eutypa or Phomopsis symptoms was found. No correlation was found between total Eutypa and Phomopsis symptoms and metres of unproductive cordon.

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Although no correlation was observed between the amount of unproductive cordon measured in blocks and the number of shoots observed to have Phomopsis symptoms, no count of shoots later in the season was performed to validate this. Therefore, it cannot be ruled out that Phomopsis damage was causing the loss of shoots, and potentially crop, pre-harvest.

Úrbez-Torrez et al. (2013) found that Phomopsis was causing discolouration in wood similar to Eutypa and Botryosphaeria symptoms and that Phomopsis was responsible for the lack of spring growth and bud mortality. As the vine health study found no correlation between metres of dead wood and amount of symptoms observed on green tissue in the same season, future work could focus on whether severity of foliar symptoms correlates to future unproductive wood.

Sclerotinia-like symptoms were observed in a total of 26 shoots, or 0.1% of all shoots monitored. The symptoms appear as blackened spots at the base of green shoots. Of blocks surveyed, 6% of sites had some associated scale infection. However, out of the total shoots counted only 1% could be said to be scale infected. This was identified as adult scale present on the two year old spur from which the monitored shoots are growing. A typical Vine Scale infestation with attendant ants is shown in Figure 13.

Figure 13 Scale on spur with ants.

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Mite damage was identified in 33% of sites monitored, with the total number of shoots affected at 3%. Bernard et al. (2005) have shown that severe mite infestations caused restricted spring growth symptoms, however, they did not quantify incidence of mite damage in the field.

While mite damage is relatively low in incidence - compared to Phomopsis or Eutypa symptoms, shoots can be very severely affected – often with little or no bunches evident, or even completely lacking a growing tip (Refer Figures 14 and 15). This may be contributing to less than optimal vineyard performance. However Hluchý and Pospíšil (1992) could not conclude that bud mites caused any significant yield loss.

Figure 14 Shoot with mite damage.

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Figure 15 Mite damage.

Disease diagnosis

Thirteen samples of dead cordon were analyzed for pathogens. The samples were selected based on significant length of dead arm, not to confirm pathogens based on foliage symptoms. Of the thirteen samples, Phomopsis was detected in eight, Eutypa in five, and Botryosphaeria in three. Nine samples had only one pathogen, while the remaining four had a combination of pathogens - including one with Fusarium and one with Phaeocremonium.

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Assessment of frosted and non-frosted blocks

The average number of shoots per metre of vines identified as frosted in 2006 was 25.87, while 25.83 were identified as not frosted. A small number of blocks have not been confirmed to have been frosted or not. These blocks had an average of 23.5 shoots per metre of cordon. The percentage of cordon identified as unproductive from frosted and unfrosted vines was 18.5% and 17.1% respectively. This is a difference of 1.4 cm per metre of cordon. For those blocks of unknown status the percentage of unproductive cordon was 17.7%.

The percentage of unproductive cordon for blocks designated as both ‘old’ and frosted is 21%, while vines designated as ‘old’ and not frosted showed the same percentage of unproductive cordon. For blocks designated as ‘young’ the amount of unproductive cordon was 15%, whether the block had been frosted in 2006 or not. From the data gathered there appears to be little correlation between dead arms and frost damage suffered in 2006. The frosts do not appear to have significantly affected vine health either; vines that had suffered frost damage had no less shoots than those that escaped damage.

Conclusion

Of green tissue surveyed, Phomopsis symptoms were the most prevalent. Eutypa symptoms are not as common, however when they occurred shoot growth was more severely affected.

Vine age appears to correlate better with the amount of unproductive cordon in a block than whether a block has been frosted or not. It is known that Eutypa expression varies between seasons, and in this season in Coonawarra, it was also no indicator of the amount of dead arm in a block. The number of shoots with Phomopsis did not correlate with the length of unproductive arm either. It cannot be concluded from this study that frost damage caused areas of bare or dead arm.

There is no correlation between number of shoots in a block and the amount of unproductive cordon. The data suggests that across Coonawarra, although trunk diseases and unproductive cordon are a problem, inherent vine health is not in decline.

It appears that as vine cordons are becoming unproductive shoots become more concentrated in sections along cordons as the total number of shoots does not significantly change. It would seem that reworking of vines is viable providing Eutypa infection has not reached the old wood to be retained and pruning wounds are sufficiently protected. This was the same conclusion made by Sosnowski et al. (2011) in their study.

While Eutypa is commonly identified in Coonawarra, the disease diagnosis showed Phomopsis was more prevalent in wood samples. (For additional information on Eutypa dieback refer to the ‘Factsheet’ in Appendix 1)

Research by J. R. Úrbez-Torrez et al. (2009 and 2013) has shown that many different pathogens infect grapevine wood and cause necrotic staining and dieback of vine arms. This has been confirmed by Barbara Hall and Mark Sosnowski (personal communication); that a complex of pathogens is likely to be causing damage to Coonawarra vineyards, with Eutypa the lead perpetrator. The strategy for managing this complex of pathogens is the same in every case; removal of infected wood.

As sections of bare arm may have live wood it is possible that the length of unproductive vineyard cordon will vary from year to year if blind buds burst at the base of spurs or along the cordon.

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Acknowledgements

This research project was funded by the Coonawarra Grapegrowers Association (now Coonawarra Grape

and Wine Incorporated) as part of the 2012 annual scholarship program, which is designed to promote

the ongoing development and understanding of Cabernet Sauvignon growing in Coonawarra.

Sarah Bird and Kerry DeGaris assisted extensively in the collection of data for this research project.

References

M. B. Bernard, P. A. Horne and A. A. Hoffmann (2005) Eriophyoid mite damage in Vitis vinifera (grapevine) in Australia: Calepitrimerus vitis and Colomerus vitis (Acari: Eriophyidae) as the common cause of the widespread ‘Restricted Spring Growth’ syndrome. Experimental and Applied Acarology, 83-109.

M. Hluchý and Z. Pospíšil (1992) Damage and economic injury levels of eriophyid and tetranychid mites on grapes in Czechoslovakia. Experimental and Applied Acarology 14, 95 - 106.

M. R. Sosnowski, D. Shtienberg, M. L. Creaser, T. J. Wicks, R. Lardner, and E. S. Scott (2007) The Influence of Climate on Foliar Symptoms of Eutypa Dieback in Grapevines. Phytopathology 97, 1284-1289.

M. R. Sosnowski, T. J. Wicks and E. S. Scott (2011) Control of Eutypa dieback in grapevines using remedial surgery. Phytopathol. Mediterr. 50 (Supp.), S277 – S284.

J. R. Úrbez-Torrez, P. Adams, J. Kamas and W. D. Gubler (2009) Identification, incidence and pathogenicity of fungal species associated with grapevine dieback in Texas. Am. J. Enol. Vitic. 60:4, 2009.

J. R. Úrbez-Torrez, F. Peduto, R. J. Smith and W. D. Gubler (2013) Phomopsis dieback: a grapevine trunk disease caused by Phomopsis viticola in California. Unpublished paper.