Developing and Assessing Different Cordon Establishment Techniques for Long-Term Vineyard Management

Abstract

This project investigated the impact of different permanent cordon training techniques on vine performance in the years immediately following cordon establishment. The treatments included cordons that were wrapped very tightly around their supporting wire, a method common in Australia and certain other winegrowing regions, as well as other less constrictive training methods. Measurements of vegetative growth at one site including cordon circumference and pruning weight suggest that the growth of tightly wrapped cordons may have been hindered by the constrictive nature of their training method. Other measurements however, including plant area index did not find this to be the case. A treatment involving the use of two parallel cordon wires around which arms were trained in a loose, s-shaped bend actually showed the greatest reduction in plant tissue area. Differences in harvest parameters between training methods such as yield and grape chemistry were minimal and did not follow a meaningful pattern. Differences in bud fertility and the occurrence of primary bud necrosis were also minimal. Investigating carbohydrate status, there was a trend at one site where starch concentration was lower in shoots from cordons placed on top of the wire than other treatments in the later seasons. While this suggests the treatment may have been beneficial in promoting the translocation of carbohydrates to the perennial structures of the cordon, the same effect was observed in the proximal, intermediate, and distal sections of the cordon, suggesting the impact of the treatment on the movement of carbohydrates along the cordon arms may have been limited. Using micro- CT, it was discovered that cordons which were wrapped tightly around the cordon wire had significantly smaller xylem conduit volumes relative to total cordon volume, as well as thinner xylem vessels and less connections between vessels per unit volume. Additionally, the theoretical specific hydraulic conductivity (Ks) of tightly wrapped cordons was much lower than other treatments (p < 0.0001), suggesting that their capacity for normal hydraulic conductivity was negatively impacted by the treatment. It was determined that a vigour-based length adjustment performed on new cordon arms during their establishment was beneficial in promoting early vegetative growth, particularly in the middle of cordon arms. The benefits of the method were limited to one season however, as control cordons had no more missing spur positions than length adjusted cordons after the first season of growth. Further research in this area should focus on a lower vigour setting. A survey was conducted on older commercial vineyards to investigate the relationship between cordon strangulation resulting from tight wrapping, dieback, and the expression of fungal trunk disease symptoms. Rather than finding strangulation to be a driving force behind dieback, there was actually a trend observed where the cordons displaying the greatest degree of strangulation displayed the least amount of dieback. While the results of this survey were unexpected, the quantitative scale presented for the use of the assessment of degree of strangulation is a novel tool that could be useful in future research. Overall, the results suggest that the newly established cordons trained in the most constrictive fashion (tightly wrapped around the cordon wire) performed the worst over the course of the project. Interestingly, this was true even in the case of breakage caused by mechanical damage, which cordons trained in this manner are purported to be less prone to due to improved canopy stability. Because the project was limited to a timeframe of four years, it is likely that the negative trends developing with the practice of tightly wrapping developing cordon arms around the wire would continue to worsen over time with continued observation. The poorly developed vascular systems seemingly attributable to this training method in particular suggest that its use should potentially be avoided.