Is early defoliation a sustainable management practice for mediterranean vineyards? Case studies at the portuguese lisbon winegrowing region

Abstract

Context and purpose of the study ‐ Recently early defoliation (ED) has been tested in several high‐ yielding grapevine varieties and sites aiming at reducing cluster compactness and hence, regulating yield and susceptibility to botrytis bunch rot infection. The reported results have been generally positive, encouraging growers to use this canopy management technique as an alternative for replacing the conventional time‐consuming cluster thinning and, simultaneously, as a sustainable practice to reduce the use of fungicides. However, ED increases berry sunburn risks and/or can induce carry‐over effects on vigor and node fruitfulness as shown in the two case studies reported in this work.

Material and methods ‐ Two ED experiments were set up at a commercial vineyard located in the Lisbon winegrowing region with the varieties Aragonez, syn. Tempranillo (2013‐2015) and Semillon (2018). In both experiments the ED treatment was compared with the non‐defoliated (ND; control) using a randomized complete block design with 4 replicates per treatment. The ED treatment consisted of the removal of 5‐6 basal leaves and any laterals at pre‐flowering. Vegetative (leaf area and pruning weight) and reproductive components (%fruit‐set, cluster number, cluster weight, yield) and berry composition were assessed.

Results ‐ In the Aragonez experiment total leaf area at harvest and pruning weight were significantly lower in ED vines. The ED treatment presented also a significantly lower fruit‐set, berry weight, cluster weight and compactness, as well as yield as compared to the control. In the third season ED presented a significantly lower cluster number indicating a negative carry‐over effect on bud initiation induced by the early source limitation. Regarding berry composition, ED showed a higher Brix and a lower titratable acidity than the control but no significant differences were detected on skin anthocyanins. The incidence and severity of botrytis bunch rot infection was significantly higher in the control treatment. In the Semillon experiment the ED treatment showed also a significantly lower leaf area, fruit‐set, berry weight, cluster weight, cluster compactness and yield. No significant differences were detected on berry composition except for Brix where ED showed a significantly higher value. Despite the low pressure of botrytis bunch rot infection the control presented the significantly highest incidence and severity. An heat event occurred during the first week of August induced a severe and significantly higher berry sunburn in the ED treatment. Our results show that pre‐bloom defoliation is a canopy management practice with high potential for regulating grape yield and with benefits for grape health.However, in Mediterranean climates, where water and heat stress can inhibit leaf area compensation, the negative effects observed either on berry sunburn and on node fruitfulness recommends to use this practice with care or even avoid it.