Frost is a phenomenon dreaded by winegrowers, capable of causing considerable damage to French vineyards.
Understanding its effects and how to protect against it is essential for preserving the quality and quantity of harvests.
Let’s explore the impact of frost on vines and the solutions implemented by wine professionals.
Types of frost affecting vines
There are two main types of frost that can affect vineyards:
1/ Winter frost
This type of frost occurs during the vine’s dormant season, generally between November and March.
Although vines are more resistant during this period, extremely low temperatures (below -15°C) can damage vines and jeopardize vineyard survival.
2/ Spring frost
More dreaded by winegrowers, spring frosts occur when the vines have already begun their vegetative cycle.
Buds and young shoots are particularly vulnerable, and can be damaged as early as -2°C.
This type of frost is often responsible for major crop losses.
Frost damage to vines
The effects of frost on vines can vary according to its intensity and the stage of development of the plant:
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Destruction of buds: primary buds, the carriers of future bunches, can be destroyed, resulting in a direct loss of harvest.
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Tissue browning: young shoots and leaves affected by frost turn brown and dry out quickly.
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Cell rupture: freezing causes ice crystals to form in plant cells, leading to cell rupture and tissue death.
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Growth disruption: even if the vine survives, its growth may be slowed or unbalanced, affecting the future quality of the grapes.
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Vine weakening: repeated frosts can permanently weaken vines, making them more vulnerable to disease and water stress.
Factors aggravating the risk of frost
Certain factors can increase the vulnerability of vines to frost:
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Topography: Valley bottoms and low-lying areas are more exposed to radiative freezing.
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Moisture: Moist soil increases the risk of frost through heat conduction.
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Phenological stage: The further advanced a vine is in its cycle, the more sensitive it is to frost.
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Grape variety: Some grape varieties bud early, making them more vulnerable to late frosts.
Methods to combat frost in vineyards
In the face of this threat, winegrowers have developed a number of protective strategies:
Passive methods
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Choosing late-budding grape varieties
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Late pruning to delay budburst
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Vines planted on well-exposed slopes
Active methods
1. Candles and heaters: placed between the rows, they warm the ambient air.
2. Water sprays: form a protective layer of ice around the buds.
3. Antifreeze towers: antifreeze towers stir the air to mix the cold and warm layers. This is obviously the technique we recommend at Ventigel
4. Helicopters: draw warm air down to the ground (an expensive but effective technique).
5. Heating cables: installed along the trellis wires, maintain a positive temperature around the buds.
Economic impact of frost on the wine industry
Frost episodes can have disastrous economic consequences:
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Crop losses of up to 100% in extreme cases
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High cost of protection methods
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Impacts over several years (weakening of vines)
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Fluctuating wine prices due to scarcity of certain vintages
In 2021, for example, April frosts caused an estimated 25% drop in production compared to the average of the previous five years in certain French regions.
Adapting winegrowing practices to climate change
Climate change is accentuating the risk of spring frosts by encouraging early budburst followed by cold spells. Winegrowers must therefore adapt their practices:
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Varietal diversification
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Modification of pruning and vine training techniques
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Investment in modern, environmentally-friendly protection systems
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Taking out appropriate crop insurance
Conclusion
Frost represents a serious threat to vineyards, capable of compromising an entire harvest in a matter of hours.
Faced with this challenge, the wine industry is constantly innovating and adapting. The combination of preventive methods and active protection techniques can limit damage, but the cost and environmental impact of certain solutions remain major concerns.
The future of viticulture will necessarily involve a better understanding of microclimates and greater anticipation of climatic risks.
FAQ: frequently asked questions
How can you tell if your vines have frozen?
Visible signs include browning of young shoots and leaves, and blackening of buds. A simple test is to cut a bud: if it’s brown inside, it’s probably frozen.
At what temperature do vines freeze?
Damage can start as early as -2°C for young shoots and buds in spring. In winter, vines can withstand temperatures as low as -15°C.
Why burn straw bales in vineyards?
The aim of this technique is to create a smoke screen that limits heat loss from the soil by radiation, thus protecting the vines from radiative frost.
How to protect your vines from frost?
Methods include the use of candles, water spraying, air mixing by antifreeze towers or helicopters, and the installation of heating cables. The choice depends on the size of the vineyard and the available budget.
What causes frost in vineyards?
Frosts can be caused by cold air masses (advective frost) or by heat loss from the ground on clear, calm days (radiative frost). Topography and soil moisture also play an important role.