Yuichi Ando, Bragato Research Institute

The rise of vineyard and labour costs required for maintaining high-quality grape growing poses challenges to vineyard financial sustainability. In Marlborough, vineyard expansion is showing no signs of slowing down, accelerating regional labour shortage issues. These challenges signal a need to explore alternative growing systems for producing Sauvignon blanc.

One of the biggest vineyard expenditures is winter pruning, and for a long time, cane pruning has been the favoured pruning method in the region. Cane pruning delivered sufficient yields each year, meaning there was little appetite to search for an alternative pruning system, and spur pruned Sauvignon blanc was believed to have lower fruitfulness.

Modified spur-pruned Sauvignon blanc vines, with longer spurs than traditional two-bud spurs, were quietly trialled among some growers 20 years ago. The anecdotal feedback was that the system could produce equal or more yields than cane pruning while reducing labour inputs and pruning cost, but it was never tested under an objective trial setup. Also, there were limited demonstrations of the effects of the different pruning systems on the quality of grapes with equal bud loads in the New Zealand context.

The trial

In 2020, the entire horticulture industry encountered an unprecedented challenge due to a shortage of seasonal labourers caused by New Zealand border closures. This led to many vineyards experiencing delayed pruning, or worse, pruning during bud burst. To prevent a recurrence of this crisis, Bragato Research Institute (BRI) actively sought solutions, including a long spur pruning technique pioneered by Mark Allen, a viticulture consultant. Long spur pruning has the potential to reduce labour inputs at a similar yield and quality, as well as enable more mechanisation than cane pruning.

BRI set up a trial to gather objective data on the effectiveness of long spur pruning across three Marlborough vineyards to give growers the new knowledge they need to decide whether this alternative pruning technique was appropriate for their circumstances.

Methodology

The trial compared the typical Marlborough pruning system of four canes per vine to two long spur techniques. Four cane vines (4C) as control were laid with the specific bud number set by the vineyard target. Four bud-spur vines (4BS) consisted of the same bud numbers as 4C but pruned with four bud-spurs, and five bud-spur vines (5BS) had the same spur number as 4BS but each spur had laid with five buds, e.g. 23% increased bud numbers than 4C.

Figure 1: Long-spur pruning treatments. Photos showing the third-year long-spur vines pruned in winter 2023.

Three treatments were applied to four adjacent vines in a bay and replicated six times with a complete randomised block design. Three vineyards grown in moderate soils with 15 to 20-year-old vines in the Wairau Valley that have been producing over 15 t/ha were selected and monitored for two years from the winter of 2021.

The effects of long spur pruning on vine performance and wine quality were investigated each season by measuring vegetative and reproductive responses, disease assessment, wine compositions, volatile aroma compositions, and sensory evaluations.

Key findings from the trial

Blind bud and shoot density

Compared to 4C, 4BS and 5BS vines had higher blind buds in all vineyards for season one, and two vineyards in season two. Blind budding in long spur vines was mainly observed at the first bud from the base of the spur at an incidence rate of about 50%.

Although 5BS recorded significantly higher blind buds than 4C, 5BS tended to have a higher shoot number per linear metre, which was likely the reflection of a higher bud density retained. Blind budding at the first bud can lead to spur casting over time, limiting canopy growth and impacting yield and quality.

To mitigate this risk, the finger and thumb technique was introduced during the second season’s pruning where the spur site was lifted and it helped lower those spur sites at the following year’s pruning.

Canopy density and architecture

There were no differences in the percentage of canopy gaps and interior bunches using point quadrant analysis in season one, but image analysis showed that cane-pruned canopies had more porosity than spur-pruned vines. However, the differences in the canopy gaps between treatments disappeared once vines reached full canopy in February. During the second season, there was a tendency to have higher leaf area in spur pruned vines using an area meter, but the difference was only significant in one vineyard.

Yield, bunch architecture, and juice compositions

Fruit yield exceeded the target of 15 tonne/ha set at the beginning of the experiment for all but 4BS in one vineyard in both seasons. Compared to cane pruned vines, 4BS tended to have lower yields, but the differences were less noticeable in the second season, except for in vineyard 4. In the second season, 5BS yielded significantly higher than other treatments in one vineyard.

There were few differences in fruit composition in season one. Juice-soluble solids were higher in spur pruned vines in two vineyards in season one and one vineyard in season two. These seemed a reflection of lower yield in spur vines, which was less noticeable in the second season.

Diseases

Pruning treatments did not affect the disease occurrence in both years, except for 5BS, which had a lower botrytis incidence in one vineyard second season.

Wine evaluations

Wine compositions were similar between treatments. In season one one vineyard had a lower pH and higher TA and Malic acid in 4C. This was likely the reflection of the significantly higher yield in the treatment than long-spur treatments. There was no difference in season two.

Overall, there was no noticeable difference in wine sensory attributes across pruning treatments in both seasons. Each season of wines made from each treatment were served to experienced Marlborough winemakers for sensory evaluation. The panellists scored a rate of one to ten for each descriptor relevant to Marlborough Sauvignon blanc aromas and mouthfeel.

Conclusion

The comparison of four cane pruning and long spur pruning on Marlborough Sauvignon blanc over two seasons has provided valuable insights into vineyard management practices and their impact on various parameters. The findings indicate that long spur pruning had higher blind budding than cane pruning, which may have reflected lower yield in 4BS than 4C in season one. Although pruning treatments influenced canopy density, architecture, yield, and fruit composition, there was no notable difference detected in wine sensory attributes evaluated by experienced winemakers.

The project is now in its final season. In addition to the measurements discussed here, BRI will also collect information on field and financial data from growers who have been implementing the long-spur pruning system at a commercial scale. By evaluating three-year objective data and growers’ information, the project aims to determine if long spur pruning can be a viable alternative system in the Marlborough region.