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22c. CCRTwV Looking Back Looking Forward

Coonawarra Rootstock Trial
Looking back and looking forward
Report initially prepared by Nick Dry (Foundation Viticulture) in June 2020 and added to by Suzanne McLoughlin (Vinehealth Australia) in October 2020

Abstract
The key objective of the project was to compare the performance of 8 rootstocks (1103 Paulsen, 140 Ruggeri, 110 Richter, Ramsey, Börner , Merbein 5489, Merbein 6262, Merbein 5512) and an own rooted control using Cabernet Sauvignon as the scion variety. The trial was set-up using a replicated, randomised design and viticulture data collection occurred over three seasons 2014/2015, 2015/2016 and 2018/2019 with small-lot wines produced in 2019. The trial showed that rootstock has a significant effect on yield, vine vigour and wine style. It also highlighted the potential of new rootstocks Merbein 5489, Merbein 5512 and Börner for the Limestone Coast region.

Executive Summary
The Coonawarra Rootstock Trial established in 2009, is a long-term partnership between Coonawarra Vignerons, Treasury Wine Estates and Vinehealth Australia and is the only formally-managed rootstock trial of this type in South Australia.
The aim of this trial is to increase the level of knowledge on rootstock performance in the Limestone Coast by comparing 8 rootstocks (Merbein 5489, Merbein 5512, Merbein 6262, 140 Ruggeri, 1103 Paulsen, Ramsey, Börner, 110 Richter) and an own rooted control on the principle soil type of the Coonawarra. The trial was setup to facilitate scientific analysis, with both a randomised, replicated section of seven rows from which three years of viticultural measures have been recorded, as well as 27 commercially managed rows. Viticultural data collection was undertaken in the 2014/2015 (V15), 2015/2016 (V16) and 2018/2019 (V19) growing seasons. Winemaking was completed in the V19 season.
It is recognised that increased knowledge of rootstock performance in the region will help growers in the Limestone Coast be more confident in making a rootstock selection that is appropriate for their site. This will in turn increase rootstock use in the Limestone Coast and ultimately provide greater biosecurity preparedness from the threat of phylloxera.
The trial results suggest that new rootstock’s Merbein 5489, Merbein 5512 and Börner have good potential in the region and this should provide impetus for commercial plantings of these rootstocks. It must be stated however that the Merbein rootstocks have been hard to access by industry because the establishment of mothervines and subsequent distribution has been limited to two nurseries only. The current model for the supply of these CSIRO developed rootstocks needs to be reviewed to allow for wider access by industry to ensure that there is broader uptake on the significant industry investment into the development of these rootstocks.
Overall the trial results showed that the influence of rootstock on vine vigour was a key factor in explaining vine performance related to yield, wine quality and style and has highlighted the challenges of managing a replicated trial with rootstocks which inherently impart different levels of vigour to the scion. If one were to take a narrow view of the trial results, then it would be possible to quickly dismiss some of the rootstocks in this trial as not suitable to the climatic conditions in the Coonawarra. However, it was the homogenous management regime, coupled with the climatic conditions that led to the relatively poor performance of the higher vigour rootstocks. Further trial
work needs to be undertaken to understand how the high vigour/drought tolerant rootstocks can be consistently managed for quality outcomes under the conditions of the region.Acknowledgements

The project team gratefully acknowledge:
• The $30,000 funding by Wine Australia through the Limestone Coast Grape and Wine Council for the small lot winemaking and Pivot tasting.
• The continued funding of this trial by Coonawarra Vignerons and South Australian vineyard owners through Vinehealth Australia.
• Treasury Wine Estates for their in-kind contribution of operational management of the trial site and allowing the project team and local grapegrowers and winemakers access to the site.
• The in-kind contributions of many personnel who have played a part in the trial to date.

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