We all know we’ve had a very hot start to the season. The accumulated heat (the sum of temperatures over 10°C) to this point of the growing season has been perhaps the highest on record. We have had 18 days over 35°C and 4 days over 40°C.
This heat has promoted early and rapid development of grapevine canopies, resulting in high vine water use. At this time of season with canopy development almost complete, sufficient water must be applied, not to promote additional growth, but to ensure vine functions related to berry sizing and crop ripening are not adversely affected by moisture deficits. Over the past week, the water use of healthy vine on a typical plant spacing (3x2m) may have been 25-30 litres per day. This must be applied to avoid soil drying. It is important to constantly check irrigation systems, soil moisture levels and crop health leading up to, during and after periods of extreme heat.
Adequate soil moisture levels are also required to help protect the grapes against sunburn during these days of extreme heat. The water transpired (lost) from the stomata of leaves has a cooling effect on the leaves and the surrounding environment. The higher the transpiration rate the greater the cooling effect in the vineyard. Evaporative cooling from the wetted soil will also contribute to lower leaf and fruit temperatures. With veraison starting in some varieties, the dangers of sunburn damage increase, particularly for susceptible varieties such as Gordo. In such varieties, the application of clay-based sunscreen products may also be considered to minimise the risk of crop loss.