New technological tools for yield regulation in minimal hedge pruned vineyards: preliminary results

Abstract

Good grape quality and cost efficiency are the main objectives in grape production.  Cost reduction can be achieved by using forms of minimal pruning. The minimal hedge pruning (MHP)-system with mechanical yield regulation is a new way of grape production for basic quality wines in established espalier vineyards.

In Franconia (Northern Bavaria/Germany) different mechanical techniques for yield regulation were tested in hedge-pruned vineyards in the years 2011 and 2012. Besides the experiences with grape harvesters during berry development, first experiences were gained with new machines e.g. vertical rotational string thinners (VST).

VST were used after flowering and resulted in a good cluster thinning, but also in strong defoliation and in numerous shoot injuries. Yield regulation by using grape harvesters during the pea-stadium of the berries turned out to be successful, too.  In both variants the determination of the desired reduction level was very difficult.  For both techniques the right moment of cluster thinning is crucial.

One side effect of mechanical yield regulation is a delay in grape ripening, mainly in the first transformational year.  The delay is particularly increased if the regulation is carried out by VST. The degree of yield regulation and also the degree of leaf and shoot damage by VST depend on the material, the strength of the plastic strings and the rotation and tractor velocity as well.

The grape quality in VST trials, mainly the sugar content and the proline level in must, and furthermore the sensoric value, were significantly lower in comparison to vertical cane-pruned (VCP) vineyards.  In the second year of hedge-cultivation due to the higher wood proportion higher must and wine quality values were reached.  Under the effect of climate change, which will result in higher alcohol content and earlier grape maturity, new technical possibilities with the side effects as e.g. grape maturity delay for early ripening varieties will gain more interest in grape production.