Mitigating Heat Stress in Vineyards

Climate change continues to affect weather patterns across all regions in South Australia. Managing the increasing instances of heatwaves has become challenging, prompting researchers, viticulturists and winemakers to investigate practical strategies to mitigate the increase in frequency and intensity. The focus is to improve vine resilience, maintaining yield while preserving berry quality during these events.

According to the Bureau of Meteorology (BOM), a heatwave is defined as 3 or more days in a row when both the day and night time temperatures are usually high in relation to the local long term climate averages.

The BOM uses the ‘excess heat factor’ (EHF) index to monitor and forecast these events. The EHF combines:

• A comparison of the average temperatures for a 3-day period with what would be considered hot at that location
• The observed temperature at that location over the past 30 days. (www.bom.gov.au)

Recent heatwaves in 2019, 2020, and 2021 led to varying degrees of crop damage, ranging from minor to complete crop failure. Additionally, I have also observed instances of significant berry damage during isolated events with temperatures exceeding 38°C, particularly during the vulnerable stages of flowering and veraison.

There are many ways in which we can reduce the impacts of heatwaves including:

• Irrigation management - maintaining soil moisture levels enabling the vine to transpire (contributing to vineyard cooling), and to regain their turgor overnight (Hayman et al, 2012).
• Evaporative cooling – when water evaporates, it absorbs heat energy from its surroundings, thereby lowering ambient temperature.
• Canopy management – adjusting canopy density, row orientation, and canopy height, can regulate the amount of radiation reaching the bunches, reducing the risk of burn and excessive heat accumulation. Techniques such as leaf removal, trimming, and foliage manipulation applied to optimise canopy microclimates.
• Soil improvements – cover crops and mulches, to reflect solar radiation reducing heat absorption, reduce evaporation and maintain cooler soil temperatures alleviating heat stress on grapevine roots.
• Reflective materials - shade cloth, and sunscreens, reflecting solar radiation at the fruit zone.

This report outlines the techniques and strategies employed to manage heat in the countries visited. Nuffield travel was postponed due to the COVID 19 pandemic, allowing Bleasdale Vineyards the opportunity to adopt some of these findings. The report also details the advantages, and challenges Bleasdale Vineyards encountered implementing some of these practices.