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Keywords:

  • berry weight;
  • defoliation;
  • fruitset;
  • mechanization;
  • source–sink balance

Abstract

Background and Aims:  The number of pre-bloom source leaves is a primary determinant of subsequent fruitset. Accordingly, we tested whether pre- and post-bloom hand (HD) and mechanical (MD) defoliation are effective in limiting the yield of a high-cropping cultivar such as Sangiovese in a 3-year field study.

Methods and Results:  The first six basal leaves and any laterals were removed by hand, and the same area was subjected to MD, the latter removing 48.3% of the leaf area removed manually. Both treatments significantly reduced fruitset, yield per shoot, bunch weight, berries per bunch and bunch compactness. Yield/ha declined from 32.8 tons in control vines to 24.4 and 19.0 tons for MD and HD (pre- and post-bloom treatment means), respectively. Leaf-to-fruit ratios were unaffected by defoliation as source loss was fully offset by yield decline. Soluble solid concentration and total anthocyanins on a fresh-weight basis increased by 2.4°Brix and 0.2 mg/g in HD and by 2.2°Brix and 0.08 mg/g in MD as compared with that in non-defoliated control.

Conclusions:  Although results from HD reinforce the physiological basis of the technique's effectiveness, MD proved likewise effective in reducing yield and improving grape quality.

Significance of the Study:  Early MD has the potential to regulate yield in a timely and cost-effective fashion.