Early Defoliation of 'Tempranillo' Grapevines in Semi-Arid Terroirs of Spain

Abstract

Early defoliation has been found to be an effective tool to reduce cluster compactness and improve fruit composition in different areas of northern Italy. Our objective was to test this technique under warmer conditions in 'Tempranillo' vines in two locations of Spain. In Requena (East-Spain), non-defoliated vines were compared with three defoliation treatments performed at different phenological phases (flowering or fruit set) and intensities. Sixteen vines per treatment were randomly selected in the vineyard. In the Badajoz (West-Spain) site, where vines are more vigorous, control vines were compared with defoliation carried out at fruit set. Treatments were carried out in 108 plants per replicate and four replicates per treatment. In the first season, as an average for all defoliation treatments, yield was reduced 22% by leaf pulling in East-Spain but not in West-Spain where yield was similar in all treatments. In East-Spain the yield reduction was due to lower berry fresh weight, while fruit set was not affected by defoliation. The effects of leaf pulling on grape acidity were different in the two locations, with defoliation decreasing must pH in West-Spain but with an increasing trend in East-Spain. Berry phenolic concentration increased with leaf removal in East-Spain but not in West-Spain where however cluster health was improved by defoliation. In East-Spain, the experiment was repeated during a second season, and in that year there was a heavier reduction in yield (-41%) due to lower bud fertility and fruit set produced by leaf pulling, suggesting important carry-over effects of the treatments. Overall, results indicate that even in warm terroirs early defoliation can improve berry composition but in different fashion depending on specific site characteristics. Growers should take into account that an important yield penalty due to defoliation might occur.