Experts recommend this seven-point checklist to help frost-prone vineyards prepare:1 Position and test weather sensors to provide frost warnings.
2 Late prune to delay budbreak and/or leave sacrificial canes.
3 Ensure any inter-row and headland ground cover is minimised.
4 Encourage firm inter-row soils and uncultivated ground, to reduce heat loss.
5 Remove or thin barriers to cold air flow, such as hedges.
6 Seek professional advice about suitable frost protection equipment. Here are the major options:
- Heaters: Adding heat into a vineyard is one of the most effective means of protection. If enough heat is introduced to replace all energy lost, temperatures will not fall to damaging levels. A variety of frost busters (hot air blowers) and bougies (candles) exist but they can be inefficient, costly, cause smoke nuisance and/or air pollution and are labour intensive. When there is a weak inversion layer they may not provide adequate protection.
- Frost fans: Both static and mobile frost fans exist. They pull down warmer air from above inversions and blow it into vineyards, displacing cold air. They require a strong inversion to be most effective and larger models can be noisy, but on the plus side they are tried and tested, and often come equipped with automated stop/start, GPS and remote monitoring functions, giving peace of mind and reducing labour costs.
- Sprinklers: A very effective form of frost protection. As water is sprayed onto vines it freezes and releases a little heat (latent heat), ensuring the temperature of the shoot or bud will not fall below 0°C. However, sprinkling must be continuous throughout a frost event and therefore a considerable amount of water is required, up to 30,000 litres of water per hectare per hour!
- Heating wires: Electric heating cable systems are un-intrusive and effective in low temperatures. However, beware of the potential significant power and cost of these products, and any danger posed if cut.
- Sprays: Polymer coatings can provide a degree of insulation to young shoots and buds, but there is little independent research into their effectiveness. Furthermore, they require an accurate frost forecast to inform the need to spray a vineyard.
- Cold Air Drains: Sometimes called ‘Selective Inverted Sinks’. These are fans that extract cold air vertically by drawing cold air into the bottom and thrusting it upwards to a height of nearly 80m. The cold air mixes with the warmer, less dense air until it is dispersed horizontally. These work well in areas such as valley bottoms or swales where cold air accumulates. They are automated, relatively quiet and environmentally friendly.
'Start planning before it’s too late'The numerous variables of radiation frosts mean that protection effectiveness is not guaranteed, but the alternative could be costly in terms of both crop and reputation loss. So, if you haven’t already done so, the expert advice is to start planning before it’s too late!
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Alistair Nesbitt is a viticulture climatologist with expertise in how weather and climate interface with wine production, globally. He holds a PhD in viticulture and climate science and a BSc and Master’s degree in Viticulture & Oenology. His company is called Vinescapes.