Different yield regulation strategies in semi-minimal-pruned hedge (SMPH) and impact on bunch architecture

Abstract

Context and purpose of the study – Yields in the novel viticulture training system Semi-Minimal-Pruned Hedge (SMPH) are generally higher compared to the traditional Vertical Shoot Positioning (VSP). Excessive yields have a negative impact on the vine and wine quality, which can result in substantial losses in yield in subsequent vintages (alternate bearing) or penalties in fruit quality. Therefore yield regulation is essential. The bunch architecture in SMPH differs from VSP. Generally there is a higher amount but smaller bunches with lower single berry weights in SMPH compared to VSP. By means of different yield-regulating measures, i.e. biochemical thinning concepts, harvester thinning and Darwin-rotor (Fruit Tec Maschinenbau, Markdorf, Germany) the bunch architecture in SMPH is altered. A loose bunch architecture minimizes the risk of bunch rot and improves grape health. The aim of the study was to investigate the impact of different yield regulation strategies in SMPH on the bunch architecture.

Material and methods – Under field conditions, three different thinning methods were tested on the two fungus-resistant grape varieties Rondo, Regent, and additionally Riesling at Geisenheim, Germany (49°59´20” N; 7°55´56 ” E). Both biochemical and mechanical thinning concepts were pursued. The biochemical grape thinning treatment was applied during flowering with the plant growth regulator gibberellic acid (Gibb3; Plantan GmbH, Buchholz, Germany). The mechanical thinning was performed using a harvester at berry pea size stage of fruit development and the Darwin-rotor, which was originally developed for horticultural crops and commonly used for mechanical blossom thinning by horizontally rotating strings. In the vineyard it has been used for thinning young canes a week after budburst (E-L-scale: 9). The three thinning treatments were compared to non-treated VSP and SMPH control and bunch architecture has been investigated.

Results – Lower bunch weight, berry weight and rachis weight were detected in all SMPH treatments compared to VSP. Statistically significant lower bunch weight was detected for SMPH using harvester thinning compared to SMPH thinning with gibberellic acid, thinning with Darwin-rotor and a non-treated SMPH control. No differences in rachis weight were observed between the SMPH treatments. Our results indicate a looser bunch architecture using a harvester and gibberellic acid for yield regulation compared to a non-treated SMPH control. Whereas thinning with the Darwin-rotor resulted in an increase of berry diameter and bunch weight hence more compact bunches.