Optimizing vine pruning of Pinot noir and Müller-Thurgau after extreme hail damage

Abstract

Hail damage can have a major impact on the vine’s physiological growth (defoliation, wood and cane damage) and can lead to significant yield and economic losses. Economic losses may extend into subsequent years, depending on the damage sustained and the vine’s ability to recover. With the expected increase in extreme weather events due to climate change, the frequency and severity of hail damage—and associated financial repercussions—are likely to rise. Effective solutions must be found to minimize economic losses and enable the vine to recover quickly. Pruning is known to play a key role for vine’s recovery when damage to shoots is severe.  Cordon pruning is recommended over guyot pruning, as it eliminates the risk of cane breakage and can enhance yield potential. However, the success of cordon pruning also depends on the varietal fertility of the buds.

This study, conducted between 2021 and 2024, investigates the effects of different pruning techniques following two severe hail events in Wädenswil, Switzerland (21.6 and 24.7.2021) which caused extensive damage to vines. This trial focuses on Müller-Thurgau and Pinot Noir varieties and evaluates the short-term (2022, the year after the hail event) and long-term (2023-2024 normal years) impacts of these techniques on vine recovery. One pruning variant focuses on “simple guyot” with one cane of seven to ten buds. Another variant called “double guyot” uses two canes with five to seven buds each. Two cordon variants with three or four buds per spur were implemented.  Budburst fertility, yield, grape quality, and associated labor costs were measured. Labor time per vine encompasses pruning, trellising, debudding, and harvesting, providing insights into cost-per-hectare calculations. Grape quality is evaluated for must parameters as: sugar content [Oe], PH, total acidity [g/L], wine and apple acid [g/L], formol nitrogen, and yeast-assimilable nitrogen [mg/L].

It is hypothesized that increasing the number of buds (cordon variants) should increase yield in the year following hail damage (2022). However, this is expected to reduce sugar content [Oe] and nitrogen levels [mg/L]. We expect that differences in labor costs have the greatest impact in the year following the hail event. This work aligns with previous research indicating the importance of adaptive pruning strategies for vine recovery after a hail damage, particularly for low-fertility varieties such as Müller Thurgau and Pinot Noir.