Technical Yearbook 2024

Observations: three divergent scenarios By the end of November the visible effect of the flood on different vineyards was already varied and the affected blocks could be divided into one of three categories. Firstly there was the lower-lying blocks that were submerged for periods exceeding three days. These blocks, representing approximately 20% of the affected area under vines, also had the most mud deposits and the impact on growth and crop load was significant. Green shoots with bunches died back completely and the subsequent regrowth response was sluggish with little or no grapes present. By the end of December these blocks still had a bushy appearance, with many short shoots and few active growing tips. The fact that soils were waterlogged for such a long time, also contributed to the delayed growth. The largest group of vineyards, which includes about 60% of affected blocks, was under water for longer than 24 hours, but not as long as the first group. The impact on the crop was significant, but differed from block to block. In most cases the shoots that were submerged died back from the shoot tip, but the flower clusters survived. The leaves were all lost however. On the remaining bare shoots, new lateral shoots developed which grew fast. The remaining flower clusters also enlarged as normal and flowering followed shortly on the heels of the regrowth response. Flowering and fruit set varied greatly between blocks with certain blocks displaying well, while other experienced poor and uneven set. A crop loss of approximately 50% or more was recorded for these blocks. Lastly there was an estimated 20% of affected vineyards where the canopy was partially or totally submerged under water for 24 hours or less. Here the regrowth response was immediate, with new leaves that formed, as well as new shoot tips which developed and grew vigorously without delay. The impact on the flowering process was minimal and these blocks produced yields comparable to their long-term averages. Most important factors that influenced the damage: • Location of the vineyard block. • Time duration under water. • The growth phase of the vineyard [vineyards at a more advanced growth phase (earlier phenology), were able to retain flower clusters, but shorter shoots (later phenology) lost their clusters]. • Cultivar (Ruby Cabernet and Chenin blanc appear to have suffered fewer losses than Colombar). • Vineyard age and carbohydrate reserves also influenced the response of the vineyards. The effect on the 2024 crop With the help of Sentinel-2 satellite images available on CapeFarmMapper website (the free agricultural resource of the Western Cape Department of Agriculture), along with producer feedback, it was determined that approximately

Regrowth of new lateral shoots with no grapes.

Although the leaves and shoot tips died from excessive mud and water in this vineyard, the flower clusters survived and developed further.

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TECHNICAL YEARBOOK 2024