Issue link: http://winesandvines.uberflip.com/i/314400
p r a c t i c a l w i n e r y & v i n e ya r d J U n e 2 0 1 4 55 g r a p e g r o w i n g Leaf removal was conducted at three phenological stages: bloom, pea-size and bunch closure. Leaves were removed from both the east and west sides of the cluster zone at each of the three pheno- logical stages by using hand labor or mechanically using an Avidor leaf puller attached to an over-the-row tractor. Treat- ments were applied to plots of 12 vines in a randomized complete block design with six replicates. Due to the nature of the season and the commercial vineyard's management policy restricting the use of specific fungicides for Botrytis control, a non-leaf removal treat- ment was not implemented. However, a third treatment where leaves were removed at bunch closure from only the east (morn- ing) side of the cluster zone was imple- mented for comparison (an industry standard practice), and leaves were removed either manually or mechanically. Leaf removal was performed at the start of each time point with clean-up passes to remove new leaves or laterals produced in the cluster zone during each successive phenological stage in the study. Vine growth parameters were monitored including fruit set, leaf area, yield, yield components (cluster weights, berries per cluster, etc.) and pruning weights. Fruit maturity, berry phenolics and incidence of Botrytis bunch rot at har- vest were also measured. Results Results from this one-year trial indicate that there is little difference between hand and mechanical leaf removal in terms of level of disease incidence on fruit, vine productivity and fruit quality. Beginning leaf removal too early in the season raises concerns about reduced fruit set resulting from potentially lower carbohydrate availability to developing flowers or from mechanical damage to inflorescences. Mechanical leaf removal conducted at bloom reduced fruit set by 11% compared to hand leaf removal at bloom and all other phenological stages using either method. This was not a major concern as fruit set was generally high across all treatments, and yield at harvest did not differ among any treatments. Despite similar yields across the trial, average cluster weight was lower for treatments where leaf removal was con- ducted at bloom (125 g) compared to leaf removal at later phenological stages by either method (140 g and 135 g for both hand and mechanical leaf removal at pea-size and bunch close, respectively). When comparing the timing of leaf removal conducted on both sides of the canopy, there was no difference in the percent of clusters with Botrytis or the percent of berries within the cluster with Botrytis infection. This suggests that ear- lier leaf removal did not help reduce the presence of the disease. When comparing the impact of side (east only compared to east and west) and method (hand versus mechanical) of leaf removal at bunch closure, method of leaf removal had greater impact on the incidence of Botrytis at bunch closure (p=0.0436) than the leaf removal on a particular side of the canopy (p=1.0000). Hand leaf removal resulted in 10% lower incidence than mechanical leaf removal at that time point. However, when looking within infested clusters, there was no difference in the percent of berries within cluster that were damaged when comparing between hand and mechanical leaf removal. On average, both hand and mechanical leaf removal treatments had 13% of berries showing signs of Botrytis infection at harvest. Applying mechanical leaf removal early in berry development is a concern, as it may cause physical damage to clus- ters, particularly in early development