by Gert Engelbrecht

Heatwaves are a reality in most wine-producing countries. Allowing vines to recover as soon as possible after extreme heat events is crucial for producing quality grapes for wine production. Given the fact that exposed leaf area and transpiration surface are among the biggest drivers of water use, researchers in Italy studied leaf removal as a strategy to reduce the transpiration rate and improve the water status, thus enabling vines to recover more quickly.

Project layout
The study was conducted indoors in a controlled environment. Two-year-old Sauvignon blanc vines grafted onto SO4 rootstock were subjected to four treatments:

• WW control                    well-watered, no leaf removal
• WW leaf removal            well-watered, 40% apical leaf removal
• WS control                     water stressed, no leaf removal
• WS leaf removal             water stressed, 40% apical leaf removal

These four treatments were subjected to heatwave conditions with temperatures above 40 degrees Celsius. Measurements included predawn leaf water potential, stomatal conductance, leaf temperature, net assimilation, etc.

Results

• Under drought stress, there was no difference between the leaf physiological parameters of WS control and WS leaf removal during and after heatwaves. Possibly due to near-complete stomatal closure.
• WW leaf removal recorded a 15% reduction in transpiration water losses compared to the WW control.

Significance of the study
Reducing leaf area to lower water use and increase plant water status will only work if good irrigation strategies are followed and extreme water stress is avoided. Further aspects need to be investigated, such as the effect of leaf removal on source-sink relations, reserve status and varietal differences, and the influence of different soil types, etc.

Reference:

Wegher, M., Niedrist, G., Tagliavini, M., Asensio, D., Giuliani, N., & Andreotti, C. (2025). Impact of leaf removal on recovery of young grapevines under heatwave conditions: A study in an ecotron environment. OENO One, 59(3). https://doi.org/10.20870/oeno-one.2025.59.3.7462