Viticulture - Minimising Storm Damage to Grape Vines

Yass Valley viticulturalists will be interested in Dr Aude Gourieroux’s (National Wine and Grape Industry Centre, Wagga Wagga) paper, “Hail and Severe Storms”, outlining how to minimise damage to grape vines from storms and hail. This summer we’ve been fortunate not to have a repeat of the hailstorm of 2020, but we have had a number of storms, some of which have been quite destructive.

As we know, once a storm is detected, it can often be too late to protect the vineyard. Plants receiving storm damage at inflorescence usually recover by growing laterals that might bear fruit at a later stage. In this instance, fruit quality is likely to be reduced because of the delayed development, lack of nutrients from damaged leaves, and possibly a loss in yield.

Storm damage before veraison will affect the whole plant, including the developing berries. Usually, the berries will either dry or drop or heal by themselves. For those that heal, they will have an uneven shape but will follow the normal development and ripening processes.

A storm during berry ripening will most likely cause the berries to suffer skin splitting, which brings with it the risk of infection by Botrytis and other rots. There are different vineyard techniques for drying the berries and avoiding or controlling these infections, however, the critical success factor is timing; if the damage occurs during the weeks before harvest, some growers might recommend sequencing harvest. This means picking damaged bunches before infection occurs, even though they have not quite reached the expected maturity. Then at the estimated harvest time, picking the remaining healthy bunches as usual.

Gourieroux recommends netting to slow down the storm droplets before they reach the vines. Netting will not completely prevent the damage but will reduce it. It is also recommended that viticulturalists promptly attend to storm damaged vines as it leaves them vulnerable to infection:

• Before veraison, assess damage and remove injured shoots and buds, and keep the undamaged bunches clear of infection. Applying a fungicide will reduce the occurrence of bunch rots and help damaged stem tissue heal.
• Unfortunately, there is not much that can be applied after veraison to prevent bunch rots. It might still be possible to harvest the grapes as long as the weather remains dry, and thus slows down the inception of Botrytis or Aspergillus (most commonly found). Removing damaged bunches will also help reduce infection spread. If the storm happens within a couple of weeks of scheduled harvest, some people recommend a subsequent harvest.

• Topics:

• Rural Roundup
• Wine / Viticulture