Shoot Thinning
The optimum shoot density is 5-6 shoots per foot of row. Thinning to this density can help reduce shading, adjust the crop, lower the risk of disease and improve spray penetration. The optimal time for shoot thinning is before the shoots reach 12 inches. Much of the state is past this point, so removing shoots may be more difficult requiring the shoots to be cut.
Shoot Positioning
In high cordon-trained systems, shoot positioning and pulling shoots off the tops of the rows can 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. These practices may need to be done multiple times throughout the season.
Leaf Removal
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.
Cluster Thinning
Cluster thinning is recommended on large clustered varieties. On average, each shoot should only have one or two clusters on it. You will want to remove clusters on any short and/or weak shoots as well. The best timing for cluster thinning wine grapes is after bloom and fruit set. Cluster thinning prior to bloom can result in compact clusters prone to disease.