Title : How does cluster leaf removal reduce grape diseases pressure on cold-hardy hybrids cultivars under climatic condition of eastern Canada
Fruit zone management (FZM) involves leafing around grape clusters and thinning clusters. One of the main objectives of the FZM is to improve the aroma, flavor and pigment profiles of the grape, promote earlier maturity, and reduce disease. Despite the apparent advantages of FZM on grape quality, the precise impact on disease development is not well documented. FZM is expected to limit the development of grape diseases such as bunch rot by Botrytis (Botrytis cinerea), downy mildew (Plasmopara viticola) and powdery mildew (Erisyphe necator). The impact of these practices involves the promotion of a microclimate less favorable to the development of the disease and better penetration of fungicides into the canopy. However, the timing of the application of the practices is crucial to have the targeted effect. Practices of fruit zone management were evaluated for their effect on disease management during summer 2019 and 2020. The practices were leafing around the cluster zone on: 1) one side of the row at nouaison; 2) two sides of the row at nouaison; 3) one side of the row at veraison; 4) two sides of the row at veraison; 5) no leafing (control). Downy mildew, powdery mildew, and botrytis bunch rot were assessed weekly on leaves and at harvest on clusters. Regardless of the treatment, the effect of FZM practices was small but significant. For both timing of leaf removal, nouaison and veraison, lower disease severity was observed when leaves were removed on both sides of rows, and this mainly on clusters. Overall, lower disease severity was observed when leaves were removed at nouaison as compare with veraison. The difference in disease severity may be explained by lower humidity and better fungicide penetration in the canopy where leaves around the clusters were removed on both sides of rows. The removal of leaves from the fruiting area promoted the penetration of fungicides during a localized treatment but also of general coverage. Results will be included in a comprehensive strategy developed to reduce disease and fungicide resistance development under northeastern conditions.