Timing of Crop Removal Has Limited Effect on Merlot Grape and Wine Composition

Cluster removal during the growing season is a widely utilized vineyard management practice aiming to balance crop load to the capacity of the vine to ripen the fruit. Research was undertaken over two growing seasons (2008-2009) in Hawke’s Bay, a cool climate region of New Zealand, to establish the influence of different times of crop removal on Merlot vine growth and fruit and wine composition. The test vineyard was high-yielding, to 23 t/ha, and vigorous. A commercial standard of apical cluster thinning to remove 20 clusters per vine from vines with ca 44 clusters in 2008 and ca 47 in 2009, was carried out on uniform vigour, 7yo grafted Merlot vines at nine times between prebloom and six weeks post veraison. The 2009 season was naturally higher yielding. Timing of crop removal had no significant effect on vine vegetative growth in terms of enhanced shoot growth as measured by cane weights at pruning, or canopy leaf density. Time of thinning also had no effect on overall grape yield, cluster weight, and berry weight. There were limited effects on fruit ripeness in one season (2009) at the veraison time of thinning only, with increased Brix and lower TA levels. Berry anthocyanin concentrations were enhanced by cluster thinning in 2008, and more so when undertaken at or soon after veraison. There was however no influence of removal timing on anthocyanin levels and total phenolics in the wines. Grape ripeness, must and wine composition tended to respond more from crop removal at veraison than the other times evaluated. Data suggest that vine response was modified by excessive leafiness and shading.