Pinot noir has tight clusters and thin-skinned berries that are extremely prone to bunch rot diseases in the cool and wet Michigan climate. It was hypothesized that leaves removed at full bloom will significantly reduce fruit set and berry number and will result in a significant decrease of cluster compactness and bunch rot severity at harvest. The experiment was arranged as a randomized complete block design with leaf removal (LR) as a categorical factor with five levels of defoliation and conducted in two years. Removal of the leaves from 8 or 10 nodes (LR-8, LR-10) resulted in a decreased number of berries per cluster and percentage of fruit set. Rot severity was reduced with LR-4 and LR-6 in 2011. In 2012, previous year defoliation reduced the size of inflorescences and their number per vine. During fruit set, sources for a cluster development were provided from the same shoot while long distance translocation of sources did not affect fruit set. Compensation in higher leaf photosynthetic rate occurred only in LR-10 and it was not sufficient to increase fruit set.
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