Wine Grape Canopy Management Practices in the San Joaquin Valley
Recent wine grape vine training and trellising studies in the San Joaquin Valley have demonstrated the influence of cordon height, foliage support wires, and quadrilateral training on vine yield, fruit composition, and wine quality. Concurrent studies in other districts have also demonstrated the beneficial effects of cluster exposure through leaf removal and other canopy management practices on grape composition and reduced fungal disease incidence. The purpose of this study was to determine the influence of several leaf removal techniques and shoot hedging on wine grape cultivars and trellis systems suitable to the San Joaquin Valley. Three leaf removal treatments — Hand, Window, and Hedge — and a check, no leaf removal were compared with French Colombard and Barbera. Leaf removal increased fruit zone light exposure in French Colombard temporarily due to its continued vigorous growth. This resulted in no fruit zone light environment differences at veraison and harvest. There were no significant fruit composition or bunch rot effects from any of the treatments in this cultivar. Hand leaf removal reduced vine yields, presumably due to berry loss from sun exposure soon after the treatment was imposed. Greater treatment effects were measured with Barbera. This could be explained by the more extreme and persistent effects of leaf removal in this less vigorous cultivar. Window leaf removal increased sunlight exposure through veraison while hand leaf removal was effective through harvest. However, this improved fruit exposure was not accompanied by any benefits in fruit composition, including soluble solids, pH, or anthocyanin content. The only treatment effects on fruit composition were reduced berry weight and titratable acidity in the Window and Hand treatments, respectively. The only positive effect was a reduction in bunch rot incidence from all of the leaf removal treatments as compared to Check. This included Hedge which did not improve fruit zone light environment at any time. This would suggest that hedging may provide adequate air circulation to reduce bunch rot while not changing the fruit zone light environment. Overall, the results further demonstrate that canopy management leaf removal has the potential to reduce bunch rot in the San Joaquin Valley. However, the rapid regrowth of vigorous French Colombard may reduce or eliminate this effect unless practiced at a later date during fruit ripening. The mechanical methods of Window and Hedge were as effective as Hand, cluster-region leaf removal in reducing rot. Thus, they would be preferable under San Joaquin Valley conditions due to economics. Leaf removal did not improve fruit composition as has been reported in cooler, coastal region studies. In fact, some leaf removal methods reduced berry weight, and titratable acidity in Barbera and yield in French Colombard. This was especially true of the more severe Hand leaf removal treatment where fruit exposure in this hot region caused berry burn. Thus, leaf removal canopy management practices in the San Joaquin Valley can be recommended for bunch rot control but are of questionable, if not detrimental, benefit to fruit composition and yield.