Alternatives to bunch thinning in yield control and its effects on quality of the grapes and wine composition in cv. Baga (Vitis vinifera L.)

Abstract

Excessive yield and frequency of some diseases are strongly correlated, so yield control is an important current issue. Fruit thinning and the application of growth regulators do not give the desired answers due to inconsistency, technical difficulties to implement and costs. Manual fruit thinning is also a time consuming operation being difficult to implement in vineyards with large surfaces; chemical thinning using ethephon is difficult to control, producing random results depending on variety, growth stage and dosage.

A 3-year trial was initiated, and the followed parameters were tested: “Double Maturation Raisonnée” (DMR) and “Early severe defoliation” (manual and mechanical, MAD and MED), as techniques to yield control of a high-yield Portuguese cultivar, Baga, which is also prone to rot due to compact bunches and thin berry skin.

The aim of this work is to compare the effects of MAD, MED, DMR and manual bunch thinning (MFT), as methods of yield control and their effects on berry composition, quality of grapes, musts and wines.

In MAD, the first six principal basal leaves were removed at bloom, while MED was performed by using the defoliation machine close to the fruiting zone on both sides of the vine. MFT was done at veraison, limiting one bunch per shoot. DMR was performed 15 days before harvest, leaving shoots and bunches hanging on the wires. A complete randomized blocks experimental design with four replications was used.

Results presented concern data from the first two years.

Defoliated vines leaf areas reduced after defoliation but were fully compensated at veraison.

MAD, MED and DMR indicated to reduce berry weight, bunch compactness and rot. These treatments also show increase leaf area per fruit weight, colour intensity, total anthocyanins and total phenolics.

Early defoliation and DMR showed to lower yield, rot incidence, and bunch compactness. These techniques showed also to increase must composition and to be cost-effective alternatives to MFT.