Now is the time to start thinking about leaf removal in grapevines. Cluster zone leaf removal can lower risk of disease, increase spray penetration and even improve fruit quality. The period immediately after bloom to 3 weeks post-bloom is the most effective time for leaf removal. Leaf pulling after this time can increase the risk of sunburn, especially on the west side of the canopy. Many growers only leaf pull on the east side of the canopy (on north-south rows) to avoid this. The removal of the basal 3-5 leaves in the cluster zone can reduce the risk of bunch rots, especially in tight clustered varieties such as Vignoles, Seyval and Chardonel. Increasing sun makes the berries less susceptible to disease and allows for rapid drying after rain or dew. Leaf removal can also improve fruit quality in aromatic varieties, such as Traminette, and can improve anthocyanin development in red varieties.
In high cordon-trained systems, pulling shoots off the tops of the rows can also help improve sunlight exposure to the leaves at the base of the shoots. These basal nodes will be retained at pruning and will provide next year’s crop; increasing sun exposure has been shown to improve bud fruitfulness as well as cane hardiness. Shoot positioning can help achieve these goals as well and may need to be done multiple times throughout the season.
Figure 1. Post-bloom leaf removal in the cluster zone on VSP-trained vines