It is important to inspect damage to plants as soon as possible after a hail event as the level of damage can be obscured by subsequent growth. Depending on the timing of the event, hail can impact on foliage, flowers, stems, branches and fruit in various ways:
- Vines can be completely stripped of leaves and fruit
- Leaves can be bruised, torn, tattered, holed or completely knocked off the plant
- Shoots and trunks can be broken or bruised and scarred
- Flowers can be knocked off or damaged, however the full extent of the damage may not show up until the inflorescences are fully expanded
- Fruit can be bruised, holed or knocked to the ground
Although damage can be extreme, plants usually recover if hail damage occurs early in the season due to reshooting from buds. Growers with hail damage insurance should contact their insurer and arrange for damage assessment.
What should I do?
The timing and degree of damage will influence the potential management strategies. Grapevines that have been completely stripped of shoots will burst from secondary buds and provide a small crop that will still ripen during the season. Varieties such as Cabernet Sauvignon, Shiraz and Gordo have relatively fruitful secondary buds but Sultana, Riesling and Chardonnay are less fruitful. In cases where grapevines have had extensive damage to the flowers and little crop is anticipated, growers may consider knocking the remaining shoots off to allow secondary buds to burst. The economics of undertaking this operation should be carefully considered.
Hail can cause wounds that harm young grapevines. If the shoots extending up to the trellis wire are badly scarred, then cutting them back and retraining a new shoot should be considered. The scarring on a shoot that will eventually become the trunk can interfere with sap flow and may provide sites for trunk diseases in the future. Unless the damage is extensive the vine will often recover quickly.
If the weather remains dry, mature vines that are properly managed should heal wounds quickly. Early-season injury just after budburst allows time for fruitful buds to be initiated in the regrowth from latent, secondary and lateral buds, with minimal effect on bud fruitfulness or crop in the following season. However later season damage, leading up to and after flowering, has been shown to reduce fruitfulness and crop in the following season. Thus winter pruning may need to be adjusted to develop spurs in appropriate locations for future crops and to retain extra buds to compensate for the anticipated lower fruitfulness.
Where bunch stems have been damaged by hail, this has little consequence for wine and dried fruit, but the scarring would make table grapes unmarketable. Damaged plants are more susceptible to pests and disease. In particular Botrytis rot can infect any damaged tissue and if weather conditions are wet toward the end of the season the crop can be extensively infected. Treatments to protect against Botrytis infection should be applied immediately after hail damage and before any further wet weather.
- Botrytis is an opportunistic wound pathogen and protection of damaged tissue should be a priority.
For more information on Botrytis see the Botrytis Questions and Answers fact sheet produced by the Grape and Wine Research and Development Corporation. Regular spray programs for other pests and diseases should be maintained. Fertiliser programs should also be continued to maintain vine health. Inspect damaged plants more regularly for pests and diseases. Following seasons of high downy or powdery mildew infection there is a potentially higher level of inoculum in the vineyard and it will be critical to apply protective fungicide sprays as soon as possible after the damage and before the next rain.
P. Dry (1986) The effects of hail damage may carry over to next season. Australian Grapegrower & Winemaker. 275:22, 24.
Correct diagnosis is essential for effective pest and disease control. A commercial diagnostic service is available at the AgriBio Bundoora.
For further information, contact:
Crop Health Services
Ph: (03) 9032 7515
John Whiting, Agriculture Victoria. Note number: AG1444. Revised: October 2012
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication