Shijian Zhuang, Paolo Sabbatini,* Tommaso Frioni, Alberto Palliotti, 
Paolo Sivilotti, and Rachele Falchi  
*Department of Horticulture, Michigan State University, 1066 Bogue St, East Lansing, MI 48824 (sabbatin@msu.edu)

One of the most important challenges of cool climate viticulture is to achieve technological fruit maturity consistently each year. Several viticultural practices are usually implemented in vineyards to advance fruit maturity and maximize berry quality. Cluster thinning is commonly used in premium grapegrowing regions to alter the sink/source ratio, advance fruit ripening, and improve fruit primary metabolism. Leaf removal in the cluster zone is used to expose the clusters to sunlight and improve canopy microclimate, reduce disease pressure, and promote secondary metabolism. We investigated the combination of cluster thinning and leaf removal before veraison on Cabernet franc vines grown in a cool climate over two seasons (2011 and 2012). Fruit ripening advanced quickly once cluster thinning or leaf removal was implemented. However, the dynamics of fruit ripening from veraison to harvest were very distinguishable between the two very different growing seasons. 2011 was a cooler year with lower ambient temperatures and low solar radiation than 2012. Leaf removal and cluster thinning significantly improved anthocyanin accumulation between 10 and 20 days after veraison in 2011. However, the boost of anthocyanin accumulation was not significant in 2012. Anthocyanin accumulation efficiency, indexed as the anthocyanin:sugar ratio, increased more dramatically than the control in 2011 than in 2012. In addition to berry ripening, leaf removal and cluster thinning also led to a more uniform berry composition at harvest than the control. However, in the warm year (2012), this effect was not significant. The effects of leaf removal and cluster thinning on berry ripening, especially on anthocyanins, were highly modulated by the seasons, and treatments may be more beneficial for fruit ripening and berry composition at harvest when the season is cooler than an average vintage.

Funding Support: AgBioResearch at Michigan State University (Project GREEEN); Michigan Grape and Wine Industry Council; MSU Southwest Michigan Research and Extension Center