29 October 2021
Hailstorms hit several grapegrowing regions in South Australia yesterday and hail has been reported today in Victoria. The extent of the damage has yet to be assessed . Most of the affected vineyards are at a phenological stage between E-L 15 (eight leaves separated) and E-L 23 (50% cap fall). At this stage of growth and development the following symptoms can be observed in affected vineyards:
- Vines can be completely stripped of leaves and inflorescences
- Leaves can be bruised, torn, tattered, holed, or completely knocked off
- Shoots and trunks can be broken or bruised and scarred
- Inflorescences can be knocked off or damaged, although the full extent of the damage may not be obvious until after a few days when the damaged inflorescences start to shrivel
- Compound/lateral buds located on current season’s shoots can be damaged, affecting the development of fruiting buds for the following season.
While the damage caused by hail can be severe and devastating, there are important actions and decisions to be taken in the wake of a hail event.
- It is recommended to assess damage as soon as possible after a hail event, to determine the level of crop loss and the best management strategy before the damage is obscured by new growth. A follow-up assessment may be needed to determine the full extent of the crop loss as damage to inflorescences may take several days to become obvious.
- Protection of damaged tissue from Botrytis should be a priority, particularly in wet or humid conditions. Treatments to protect against Botrytis should be applied immediately after hail damage and before any further wet weather.
- Where the trunk or cordon has been damaged (particularly in young vines), a spray aimed at reducing the risk of Eutypa and Botryosphaeria should be considered. The active ingredient tebuconazole is registered for use against both Eutypa and powdery mildew and can be used up to E-L 29. To be effective against Eutypa, the spray must be applied within a week of the damage occurring.
- Damage to shoots may result in shoots from lateral buds or secondary and tertiary buds. This can lead to clumping of shoots and/or uneven ripening that may affect fruit quality. Additional canopy management and/or selective harvesting may be needed to maintain quality.
- If the majority of shoots are significantly damaged, the damaged shoots can be cut off down to the basal buds and the vine left to re-shoot from secondary and tertiary buds. This will promote the development of healthy canes for the following season. However, given that secondary shoots are less fruitful than primary shoots and tertiary shoots are most often not fruitful, yields are expected to be 50-70% of the full crop and harvest delayed by 3-4 weeks.
- Avoid exposing vines to any further stress. Nutrition and irrigation management are important to keep vines healthy and promote even shoot growth and development. Consider applying a foliar fertiliser that contains micronutrients and amino acids to help the vines recover from the stress caused by hail damage. Foliar fertiliser and fertigation applications should be delayed until the majority of shoots have five leaves separated.
- Vines may require additional fertiliser inputs after sustaining hail damage, due to the loss of significant reserves used to push secondary shoot growth.
- Managing grapevines after hail damage (AWRI fact sheet)
- Recovery from hail damage – Grapevines (Horticulture Industry Networks)
- Hail and severe storms (NSW DPI grapevine management guide 2019 –20)
- AWRI resources on Botrytis
- Best practice management guide: Grapevine trunk disease (Wine Australia)
- Agrochemicals booklet (Dog Book)
For more information or assistance, contact the AWRI helpdesk on firstname.lastname@example.org or 08 8313 6600.