South Africa Wine Technical Yearbook 2025

PHOTO 1. Leaf scorch from heat damage causes pale brown, interveinal spots encircled by a dark brown line.

PHOTO 2. Damage to exposed grape bunches and stems causes wilting, shrinkage and ultimately dehydration.

PHOTO 4. Examples of poor root development due to incorrect planting practices.

planting practices, where vines develop J-rooting or cannot escape the planting hole due to compaction (Photo 4). Sunscreen for grapes As mentioned, grapevines naturally produce certain compounds like flavanols, which act as a sunscreen. Several trials have already been performed in various warm wine producing countries with inter alia shade nets, misting sprayers and reflective agents, to reduce sunburn damage. Out of these, the spraying of koalin-containing agents before heatwaves delivered particularly promising results. Koalin (a type of white clay) is an inert chemical that reflects ultraviolet and infrared light. Its ability to protect against sunburn damage has already been proven in various crops. Wine Australia (2014) reported that the use of koalin-containing sprays in the Hunter Valley reduced the percentage of sun damaged wine grape bunches from 47% to 15%. Row orientation Another aspect that clearly played a role in the amount of sunburn damage, was the row orientation of hedge trellis systems. Especially in the Wellington area, significantly more damage was noticed in north-south row orientations.

PHOTO 3. Roots only occur in the topsoil due to stratification in the soil, which results in poor buffer capacity against extreme heat.

Buffered vine roots Upon closer inspection, many vineyards in the area

experienced a lesser degree of sunburn damage. This was indeed the case in irrigated and dryland vineyards. One of the most important countermeasures for extreme climate events like sudden heatwaves is a buffered root system. According to the late Professor Eben Archer: “Buffered vine roots are probably the most important weapon against climate change (warmer and drier) in the Western Cape of South Africa” ( Vine Roots , 2018). A buffered root system is a deep, well distributed system which consists of thick and thinner roots. An example of a poorly buffered system can be seen in Photo 3, where roots only occur in the topsoil due to stratification in the soil that was not uplifted during soil preparation. Another common cause of poorly buffered roots is incorrect

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TECHNICAL YEARBOOK 2025