Effects of Mechanical Thinning on Yield and Fruit Composition of Tempranillo and Grenache Grapes Trained to a Vertical Shoot-Positioned Canopy

The impact of mechanical thinning using a machine harvester on yield components and fruit composition of Tempranillo and Grenache (Vitis vinifera L.) vines was investigated. Experiments were conducted in two Spanish vineyards, both trained to a vertical shoot-positioned canopy over two consecutive seasons. The height of the harvester and the position of the bow rods were adjusted so that fruit was removed by the vibration of the canopy caused by the bow rods striking the vine trunks. The Tempranillo was thinned ∼10 days before veraison and the Grenache was thinned when 10 to 15% of berries were colored. Mechanical thinning significantly reduced berry number per cluster, cluster weight, and cluster compactness; a similar amount of fruit (∼65%) was removed from both varieties. Botrytis incidence was reduced by mechanical thinning of the Grenache in 2007 and was otherwise not affected by thinning treatments. Soluble solid concentration was higher under mechanical thinning treatments over the two seasons in Tempranillo and in 2006 in Grenache, suggesting that damage to the canopy was minimal. Phenolic concentration (both berry and berry fresh weight basis) was higher in fruit from the mechanically thinned vines compared with the control (unthinned) in Tempranillo in 2007 and only on a per berry basis in Grenache in 2006. Mechanical thinning conducted with a machine harvester has the potential to be a cost-effective technique to regulate yield in vineyards with vertical shoot-positioned canopies.