Impact of defoliation on leaf and berry compounds of Vitis vinifera L. Cv. Riesling investigated using non-destructive methods)

Climate change has a strong impact on the earlier onset of important phenological stages and plant development in viticulture. Hence, the adaptation of plant management is important to reply to climate related changes on a seasonal or long-term scale. In particular, a change in precipitation and higher temperatures entails the risk negatively impacting on fruit quality. An experiment was conducted where different canopy management strategies were applied to Riesling grapevines (Vitis vinifera L. cv. Riesling) planted in Winkel (Rheingau, Germany). Leaf removal at different canopy positions using various methods (e.g. manual vs. mechanical defoliation practices) led to a reduced photosynthetic active leaf area. Through modifications of the leaf area to fruit weight ratio, the berry ripening can be altered. Leaf removal of the bunch zone impacts fruit parameter and most importantly fruit health. Four different defoliation practices within a VSP trellis system were compared to a non-defoliated control during three growing seasons in an organic treated site: mechanical defoliation above the canopy (MDC); manually defoliation prior to flowering (DpF); defoliation of the bunch zone past flowering: Bunch zone defoliation (BZD) either suction fan plucking (EB490® Binger Seilzug, Germany) and mechanical defoliation or pulsation jetting of compressed air (DmS) (Siegwald®, Germany). Non-destructive measurements using a polyphenolmeter (Multiplex®3, Force-A, Orsay, France) were performed on leaves and berries to estimate the nutrition and ripening stage.

The chlorophyll index showed the lowest values for BZD and highest for control leaves. Additionally, on-the-go measurements were established to determine leaf components achieving vineyard maps in response to nitrogen or chlorophyll index. Furthermore, the data can be used for zoning the vineyard and harvest based on such mapping. When the severity of Botrytis cinerea was compared to control all treatments showed lower disease pressure (BZD -5.3 %, DpF -3.0 % and DmS -2.3 % respectively). Yield differed between -16 % (MDC), -8% DpF, -1 % (DmS) and +1 % (BZD) compared to the control having the highest (1.4 g) and BZD the lowest (1.1 g) single berry weight with a lower bunch compactness in 2014. Defoliation treatments influence the number of cluster per vine, where the lowest were found for DpF plants, accompanied with the lowest yield per single vine. These results help understanding the canopy characteristics and offer an opportunity to adapt the vineyard management strategies to seasonal changes.