Effects of early leaf removal on cluster morphology, shoot efficiency and grape quality in two Vitis vinifera cultivars.

The effects of early season leaf removal on 'Barbera' and 'Trebbiano' cluster morphology and grape quality were examined under potted and field conditions. Potted, non-defoliated 'Barbera' vines (A) were compared to treatments in which the basal portion of the shoot (nodes 1 to 8) was defoliated at a 50 or 100% level pre-anthesis (B, C), post-anthesis (D, E) or 50% both times (F). Treatments A, C, E and F were also replicated in the field using 'Barbera' and 'Trebbiano' grapevines. Fruit-set was reduced by all treatments resulting in looser clusters than the control. The minimum and maximum reduction in cluster weight was 29 and 48% for treatments B and F, respectively, in the pot study. It was 47 and 69% for treatments F and C, respectively, in the field for 'Barbera' and 44 and 56% for treatments F and C, respectively, for 'Trebbiano'. In all cases cluster size reduction was due to reduced berry number rather than smaller berry size. Sugar concentration increased for all defoliation treatments as a result of lower yield per shoot and leaf area to fruit weight ratios (shoot basis) either similar or higher than those of controls. The amount of sugar produced per unit leaf area (shoot efficiency) did not differ significantly among treatments in the potted study or for 'Trebbiano' in the field. Shoot efficiency was reduced in the C treatment for 'Barbera' in the field. These data demonstrate the potential of early season leaf removal for crop control and improvement of fruit characteristics at medium-to-high vigor sites. Work in progress will evaluate carry-over effects and feasibility of mechanical leaf removal in the vineyard.