Frost poses a significant threat to wine production, particularly in vineyards during spring, when the vines are in the early stages of their reproductive cycle. The young buds, which eventually develop into grape clusters, are extremely sensitive to frost damage. If these buds are destroyed, it can devastate the entire crop.
Frost comes in several forms:
1. Advection or wind frost – Small ice spikes form in cold winds, potentially occurring day or night.
2. Radiation frost or hoar frost – White ice crystals appear on the ground or exposed objects like vine leaves, often when clear, cold, dry air moves into an area.
3. Dewpoint frost – When the dewpoint is below freezing, water vapor can turn directly into ice, especially in areas with moisture-laden soils.
The type of frost encountered influences the preventative and reactive measures that vineyard staff must take. As temperatures drop to zero or below, growers have limited time to save their crop. If temperatures fall to minus 2°C, the plant begins to desiccate as water within the vine moves out to the forming ice layer. Once frost fully coats the landscape, the damage is likely irreversible.
To mitigate frost risk, vineyards employ both passive and active strategies:
Passive Frost Prevention
Site Selection: Choosing the right location is crucial in preventing frost damage. Modern viticulturists have access to extensive climate and weather data, allowing for informed decisions. Planting vines on slopes helps cold air drain away, while trees, fences, or walls can divert cold air, though barriers to air drainage must be avoided. Proximity to water bodies like lakes or rivers can also help, as these act as heat stores or create more air movement.
Soil Types: Soil plays a significant role. Some soils store heat during the day and release it at night, providing a natural defense against frost. However, soils with high moisture retention are prone to dewpoint frost.
Grape Varieties and Rootstock: Some grape varieties and rootstocks are more frost-resistant. For example, Pinot Noir and Cabernet Franc are relatively cold-hardy, while Chardonnay, which buds early, is more vulnerable to spring frosts.
Delayed Pruning: Delaying pruning can postpone budburst, reducing the risk of frost damage. Double pruning, where initial pruning suppresses basal bud growth, can also help protect against frost.
Active Frost Fighting Measures
Water Sprinklers: Sprinkling water on vines can prevent frost damage by forming a protective ice layer that releases latent heat, keeping the vine tissue above freezing. Although effective, this method requires substantial infrastructure and can be costly.
Smudge Pots, Candles, and Bonfires: These methods involve generating heat or smoke to prevent frost from settling on vines. However, they are labor-intensive and not always effective over large areas.
Frost Fans: Fans, which resemble wind turbines, are used to circulate warmer air down to the vines, preventing frost formation. They can be expensive and noisy but are widely used in regions like New Zealand and Australia.
Helicopters: Helicopters are used as mobile frost fans, pushing warmer air down onto the vines. While effective in some situations, they are costly and have limitations, such as the inability to operate in very cold temperatures or at night.
Heating Wires: Installing heating wires along vine rows provides direct warmth to the buds. Although effective, this method is time-consuming to install and expensive to operate.
Antifreeze Sprays: Some experimental sprays are being tested to protect vines from frost damage, but their effectiveness is still under evaluation.
Frost-Ravaged Vine Management
After a frost event, vineyard managers must decide how to handle damaged vines. One option is to prune out the damaged material, which can prevent rot and potentially improve next year’s yield. However, there is no one-size-fits-all approach, and the severity of pruning often depends on the extent of the damage.
In conclusion, frost is a serious concern for vineyards, particularly in spring. While passive strategies focus on site selection and soil management, active measures like sprinklers, fans, and heating wires offer direct intervention. Understanding the types of frost and how to combat them is essential for maintaining healthy vines and ensuring a successful harvest.
