Evaluation of Mechanical Thinning to Improve Composition of Wines from Minimally Pruned and Machine Pruned Vineyards

The effect of different levels of mechanical thinning on growth, yield, fruit composition and wine quality of Cabernet Sauvignon grapevines was studied. Minimally and machine pruned vines were examined and compared against a bilateral cordon, spur-pruned control. Thinning treatments were performed on minimally pruned vines using a mechanical harvester equipped with bo-peep rods set at two head speeds. The moderate thinning treatment was achieved by a striker speed of 150 RPM and the severe thinning treatment by a speed of 200 RPM. Mechanically pruned vines were included in the experiment but were determined to not require crop thinning during the initial season of this study. Additionally, a minimally pruned, non-thinned treatment was studied. Wines were made from the four treatments and were evaluated for composition. Significant differences in growth and yield parameters were observed, however few significant differences were evident among treatments for fruit composition and wine quality. The preliminary results obtained through this study confirm that mechanical thinning may be used as a practical tool to control vineyard crop size. It should be noted that the timing and level at which the thinning practice is performed is of great importance to its effectiveness. Results obtained in 1996 suggest that minimal and machine pruning can produce fruit and wines that do not differ in composition from traditionally trained vines.