The heavy rain in the Western Cape over the past few days has both a positive and negative impact on vineyards.

Precipitation over the winegrowing areas in the Western Cape ranged from 79 mm in the Paarl to 28 mm outside Darling (see graph for rain distribution over various areas in the Western Cape). The good rainfall comes after a very dry winter and spring which led to lower groundwater levels than normal.

“In general, producers had to start irrigating earlier and more often than usual to meet the needs of vineyards,” says Conrad Schutte, Vinpro consultation services manager. “More frequent load shedding has an enormous impact on irrigation schedules where producers, especially in intensive irrigation areas, cannot irrigate enough to meet the vineyard’s needs. The current growth phase of the vine involves cell division in berries and any stress, especially water stress, will have a negative impact on this process. This results in smaller berry sizes with a corresponding reduction in the total tonnes per hectare recovered.

“The rainfall of the last few days is extremely welcome for replenishing groundwater, relieving pressure on irrigation schedules, and encouraging berry growth and crop sizes. Dam levels will also rise after the good rains, which is beneficial for irrigation during the rest of the season.”

However, the heavy rain also increases the risks of production, especially the occurrence of fungal diseases due to the increased prevalence of free water, as well as the higher humidity and temperature.

“The weather conditions of the past few days, with rain showers followed by hot, humid conditions, were favourable for the primary and secondary infection of especially powdery and downy mildew on vineyards,” says Schutte. “Producers mostly follow preventive fungicide spray programmes and should apply follow-up sprays again after the rains as soon as they can gain access to the vineyards again. However, the risk of infection while berries and bunches are drying has increased, and the effects of this and the effectiveness of spraying programmes can only be evaluated in a few weeks.”

Random hailstorms in Paarl, Worcester and Robertson have resulted in sporadic damage with cases where canopies and bunches have been damaged, but it is still early in the growing season. Damaged grapes on bunches should dry up if treated effectively, with minimal negative effects on total crop size. Damage to vineyard roads, buildings and infrastructure was also reported and is currently being repaired.

“The rain will stimulate the vines’ vegetative growth where it is still actively growing,” says Schutte. “In these cases, canopy management practices must be applied to limit shoot growth. Fruit zones can be cleared with leaf breaking for effective lighting and air movement. This will benefit ripening and help control fungal diseases.”

Wanda Augustyn
Vinpro Communications Manager
Tel: 021 276 0458


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