Vineyard response to the floods in the Olifants River region during 2023

by | Jun 1, 2024 | Practical in the vineyard, Technical

It is not uncommon for regional producers to see vineyards against the Olifants River under water during the winter months. It is usually a welcome sight and means that the catchment areas of the Olifants and Doring River Schemes received good rain.

The large amount of vineyards established on the flood plain usually benefit from the winter floods in two ways, namely the removal and washing away of accumulated brackish salts from vineyard soils, and the replenishment of the groundwater content of especially the deeper soil layers, which alleviates pressure on irrigation during the peak growing season.


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Floods during winter: problem or not?

During winter 2023 vineyards were under water for periods of even longer than a month and this had no visible negative effect on the crop of 2024. However, it was evident that these blocks which were submerged for long periods during winter 2023, entered bud break very early with the first heat in August. This obviously made fungal control difficult, as the soil was still too wet for tractor traffic. Consequently the important first sprayings of the season were often applied too late and this heightened the risk for downy and powdery mildew.


Floods during the growing season: observations from 2023/24

Unfortunately the 2023/24 season’s floods were not only limited to the winter period. Widespread rain during the second half of September meant that approximately 1 100 ha of vineyard, including the canopy, were again submerged by the end of September. This represents about 14% of the area’s vineyard surface. By this time many Colombar, Chenin blanc and Ruby Cabernet vineyards were already at the 30 cm shoot length growth stage. There were also cultivars like Hanepoot which had not yet budded, as well as blocks that were in the process of budding or only reached 10 to 20 cm shoot length before the flood came. As the growth stages of the different affected blocks were so varied, along with other variables like cultivar, location, time under water and the age of the blocks, it was difficult to determine the damage. We were however able to record a few observations for future reference.


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Aerial photo: The Sentinel-2 satellite image of 26 September 2023 in the Olifants River with vineyard blocks indicated in red and the flood line in blue.


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.


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This bushy appearance of the hardest hit blocks was observed by the end of December 2023.


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Regrowth of new lateral shoots with no grapes.


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.


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


Poor flowering and set of clusters that survived the flooding.


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.


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Blocks that were submerged for 24 hours or less, immediately developed young leaves and new growing tips.


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 1 100 ha of vineyard were impacted by the flood of late September 2023. Out of this number, almost 100% is wine grapes (compared to table or drying grapes), with Colombar representing about 70%. For crop estimation purposes, a 50% damage loss was allocated to the affected blocks, and at the time of writing this article in March 2024, this estimate reflected a good indication of the actual crop.


The effect on the 2025 crop

From October 2023 to April 2024 the potential 2025 crop’s flower clusters already initiated, divided and elongated within the dormant primary buds. In the case of vineyards that were under water, this important process would certainly have been affected. There is particular concern over the nearly 20% of blocks that were submerged the longest (more than three days), and this is where the biggest potential crop losses for 2025 are expected.


Lessons learnt for the future

During the 2023/24 season the resilience and adaptability of grapevines were once again proven by the fact that no total crop losses materialised due to flooding. Producers who have the land available, can consider replacing the lower-lying high-risk blocks closest to the river banks with higher-lying blocks over time. There are already producers who are following this practice. The manipulation of budding dates by means of dormancy-breaking agents and pruning time adjustments is not a practical solution, because the river can overflow its walls at any time from June to December, and there is no way to predict this. In order to distribute risk, a portion of the lower-lying vineyards can be pruned early and another portion very late, at the end of September/early October. It is important to do a damage estimation for cellars and producers as soon as possible after such a flooding event, for planning and budgeting purposes. Resources like digital farm maps, new aerial photos and multispectral images make it possible to access correct information very quickly, enabling more accurate damage estimates. If the wet soils are inaccessible for tractor traffic, producers can use alternative spraying methods to execute early and timely fungal control.


For more information, contact Gert Engelbrecht at


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