Evaluation of viticultural measures to delay ripening of Vitis vinifera ‘Grüner Veltliner’

Abstract

Context and purpose of the study. `Grüner Veltliner´ is the most important Austrian white quality wine variety, which is mainly used to produce primary fruity wines. The climatic changes lead to significantly earlier grape ripening, often resulting in wines with undesirably high alcohol levels and low acidity with little primary fruit. Therefore the aim of the present study was to delay the ripening of `Grüner Veltliner´ by means of three different viticultural measures.

Material and methods. The vines were planted in 2008 at a spacing of 3.0 x 1.0 metres and raised in a mediumhigh trellis training system with a tying wire pair (h = 0.75 m) and three stitching wire pairs. Pruning was carried out as follows: two fruit canes with six buds each and two spurs with two buds each (= double Guyot). Thus, the number of buds per vine was 16 or the equivalent 5 buds per m². The trial vineyard was located on a steep slope (gradient: 36 to 39 %) facing southeast. The soil type was a carbonate-containing brown soil on flysch marl. In order to delay the development of ripening the methods “Three applications of the antiperspirant Vapor Gard® (2 % concentration) in the period after flowering”, “Total defoliation above the grape zone at the end of the development stage bunch closure” and “Keeping the canopy short at a height of 70 cm” were applied over two growing seasons in the form of four replicates per method. In the two years of trial the Huglin index was 1915 and 2105 respectively, the annual precipitation was 453 and 386 l/m² and the precipitation from April to September was 314 and 287 l/m². In the second year, the vines were irrigated by drip irrigation on the 14th, 20th and 27th of July and on the 10th of August with 33 litres per vine. In order to evaluate the effects of these maturity delay measures, selected generative and vegetative parameters were collected and analyzed and sensory wine evaluations were performed after microvinification.

Results. “Three applications of the antiperspirant after flowering” resulted in a year-dependent reduction of the sugar content in the must by 1.9 and 1.2 °KMW and of the acid content in the must by 0.8 and 0.4 g/l, respectively. Total defoliation above the grape zone at development stage “Bunch closure” also led to a reduction of must weight in both years, by 1.2 and 1.0 °KMW, respectively, without affecting acidity. In 2021, keeping the canopy short at a height of 70 cm reduced cluster weight and thus also yield compared to the control variant (-17 g per cluster and – 0,7 kg/vine). Thereby, must weight was only reduced by trend (-0.4 °KMW) and acidity was not affected. In 2022, however, the effects on the yield parameters were not significant, even though there were trends towards a reduction in yield (-0.65 kg/vine) and in cluster weight (-33 g). Neither in 2021 nor in 2022 the contents of nitrogen, potassium and total phenols in the musts were influenced by the ripening delay methods. Extra-polated pruning defoliation above the grape zone at bunch closure“ (1600 kg/ha) and “Canopy height = 70 cm” (1073 kg/ha). The values of the other two variants were 1308 kg/ha and 1313 kg/ha, respectively. In 2021, the wine of the variant “Canopy height = 70 cm” was evaluated sensorially significantly worse. However, in the evaluation of the wines of the 2022 vintage, there were no significant sensory differences.