2.8.1.c What are the best practices after a hailstorm?

When did the hailstorm occur?

In southern regions, a difference is made between early hail (before mid-June) and late hail (after mid-June). Before mid-June, several practices can be implemented in order to ensure production for the current year, but this of course depends on the damage that has been caused. Re-pruning after hail damage is possible in order to allow sufficient lignification of the new generation of shoots. However, for hail that occurs after the end of June, the measures that can be taken are more limited. Late pruning may not allow sufficient regrowth of the vine to lignify and accumulate reserves for the following year.

What should be done in the event of early hail?

If all the inflorescences are destroyed and the shoots are broken and peeled back to their base, pruning is necessary. The objective is to encourage the regrowth of shoots that can serve as a support for the next winter pruning, and to avoid any weak or bushy growth around any of the damaged areas. If the branches are not broken or peeled off and if there are still intact inflorescences, there is no need to prune again, as the development of the internodes will contribute to the renewal of the vegetation. The purpose of this pruning is to maintain four or five vigorous shoots per vine:

What should be done in the event of late hail?

When a hailstorm occurs late in the season, i.e. after the end of June, it is rarely worth re-pruning the vines. After this point, in southern regions, the growth will not have time to lignify after pruning. The vines should be left as they are. Internode development will enable, to varying degrees, the growth of new vegetation. For young or weak vines with limited reserves, it may be necessary to avoid exhausting them by removing the bunches. On adult vines, in order not to exhaust reserves, it is advisable, if the cost is manageable, to remove the damaged bunches.

Pruning of vines with late hail damage should be carried out as late as possible in the winter, taking several precautions:

• For vines planted that year: as the branches have not always sufficiently lignified, young plants can be hilled to protect them from frost.

• For two to three-year-old vines: damage is assessed by removing pieces of bark from the trunk. If the lesions reach the wood and necrosis is observed, one should not hesitate to cut back the trunk leaving two to three buds above the ground to form a new trunk.

• For adult vines: damage that only concerns the branches can cause pruning issues. As the flower buds form during June and July, hail at the end of July or August will have little effect on fertility the following year. The objective is to keep spurs with little or no damage with short pruning. For Guyot-trained vines, it is fairly easy to find a long branch with little or no hail damage.

What preventive measures should be implemented for hail-damaged vines?

Generally speaking, vines that have been damaged by hail early, whether or not they have been pruned, require increased surveillance for downy and powdery mildew until the harvest and after it. To enable good lignification, the foliage must remain functional until autumn. Moreover, the vegetation that grows back is extremely sensitive to parasites, since the young, often vigorous shoots are growing during periods when there is a high risk of disease. It is important to treat vines as quickly as possible after a hail event, if the vine in question still has leaves. Copper can be used but it has no known healing effect and risks slowing down growth. The winegrower's best ally remains favourable weather, i.e. that is warm and dry to stop white rot and enable faster wound recovery.

Another possibility is to spray herbal teas with a healing effect on the vines to help them recover from trauma, such as arnica, comfrey or valerian Disease and Pest Management.

Unfortunately, several hailstorms can occur in the same year. In the event of exceptionally low, long-lasting winter temperatures, it is possible that some vines do not then resume growth. This can be because very late summer regrowth of the vegetation has exhausted the vines' reserves. Due to the very short growth cycle, it is not possible for the vines to reconstitute their reserves before autumn.