Timing of cluster-zone leaf removal and its impact on canopy morphology, cluster structure and bunch rot susceptibility of grapes

Aims: Leaf removal in the cluster-zone has proved to be an efficient option to reduce grey mould infestation. The aim of the present work was to determine the optimal timing of this measure in practical viticulture.

Methods and results: Manual leaf removal in the cluster-zone was carried out at six time points between pre-bloom (BBCH 57) and veraison (BBCH 81) on the white varieties Sauvignon blanc (2009), Auxerrois (2009), Pinot gris (2010) and Riesling (2010). Leaf removal conducted between bloom and berries-touching led to a decreased number of interior clusters as well as a reduced cluster compactness and disease severity of B. cinerea. Prebloom and late (at veraison) leaf removal turned out to be less efficient.

Conclusion: Leaf removal between bloom and berries-touching proved to be very efficient to control bunch rot due to (i) the disaggregation of the cluster structure and (ii) the improved microclimatic conditions and can be recommended in integrated as well as organic viticulture.

Significance and impact of the study: The outcome of the present study constitutes an important tool for improving grape health status and, in consequence, wine quality under cool climate winegrowing conditions.