Frost: lessons from Champagne

What can we learn from Champagne when it comes to late frost protection?
With the Association Viticole Champenoise, and subsequently the Comité Champagne, conducting experiments into frost protection strategies since the 1930s and frost damage becoming an annual problem in European vineyards, IVES Technical Reviews looks at the region’s findings…

Passive protection

• An experiment on late pruning (November vs March) performed from 1985 to 1993 in Champagne delayed budburst for about 10 to 12 days depending on the variety (Pinot Noir, Chardonnay) and pruning method (Guyot simple, Chablis, Cordon de Royat). In 2021 and 2022, the same experiment was performed on Chardonnay with two dates of pruning (November 1 vs April 1) and two pruning methods (Guyot simple vs Chablis). A mean delay of 11 days was observed on Guyot simple and 8 days on Chablis.
• Another task linked to pruning is wrapping. For certain pruning methods (Guyot simple, Chablis), leaving the shoots unwrapped can produce a 20 to 30cm gain in height. During a radiative frost this difference can correspond to higher temperatures of 1°C or even 2°C at distal bud height.
• Tillage increases the release of humidity from the soil and the temperature 40cm above the soil can be 3°C lower than undisturbed bare ground. Given that humidity increases a bud’s sensitivity to frost, delaying soil tillage when a frost event is forecast will limit the risk of frost.
• Above soil covered by dense and high grass, temperature will be 2°C lower than above bare ground or short grass. When a frost event is forecast, mowing three to four days before the event can limit the impact of the frost without releasing humidity.
• Setting up reserves has allowed winegrowers to stock a certain amount of wine from one or several previous years for use in subsequent years. It is an effective way of maintaining quality and of buffering yield variation caused by meteorological hazards like hail or frost. Thanks to this solution, the use of frost protection methods has decreased in Champagne, thus reducing any related environmental impacts.

Active protection

All the following techniques have been tested for at least five years in Champagne.

• The principle of sprinkler frost protection is to form a “wet” ice layer that is continually freezing and releasing heat into the vine tissues which remain above a lethal temperature. This method is one of the most efficient (protection up to 100%) but requires great mastery, because starting too late will form an ice layer on the buds with a temperature under the lethal threshold. Increased monitoring is also needed to prevent pipes and sprinklers from freezing if water is directly pumped from the river. If water storage or exploration is needed, the cost can be multiplied by 3 to 4. The carbon footprint of the method is dependent on the water pump technology, but it is low, even with a petrol engine. The main issue with this method is that it requires access to a large amount of water due to its high consumption (40 m3/h/ha). An environmental evaluation of other factors related to the method, like leaching or erosion, is in progress.
• Different types of fuels can be used in burners to produce heat to maintain air temperatures above a lethal level. The efficiency of this technique is dependent on four main factors: calorific value, burner efficiency, wind speed and burner density. For example, 200 fuel oil burners per hectare are required to maintain a non-lethal temperature during a -6°C frost event with no wind (95% protection). Most French companies have stopped producing fuel oil burners and only one is still producing gas burners, the cost has therefore exploded since 2017. Other drawbacks related to the method are its very high carbon footprint (400 l/ha/h fuel oil consumption) and the polluting and harmful particles that are released into the air.
• The use of candles is based on exactly the same principle as fuel burners. Paraffin is burned to produce heat and maintain air temperature above a non-lethal value. The density of candles needs to be higher than fuel burners because of their lower efficiency. To maintain temperature during a -6°C frost event with no wind, 500 to 600 candles per hectare would be needed (90% protection). In April 2022, the cost in France was from €10-13 per candle. Considering that paraffin is derived from petroleum, the carbon footprint is not compatible with sustainable viticulture.
• Since 2018, some wood pellets burners have been tested in Champagne. The principle and the efficiency of this technique are the same as for fuel oil burners. The density is also the same, with 200 burners per hectare for a frost with a temperature of about -6°C (95% protection). The investment is around €40,000 per hectare. The pellet consumption is about €1,000 per night per hectare.
• Windmills rely on an inversion layer occurring during a radiative frost. Their efficiency is therefore dependent on the frost type. With a thermal inversion during a radiative frost, warm air can be only a few metres above the ground and within reach of the windmill. The goal is to mix the warm and cool air layers to maintain temperature above the lethal threshold for buds. The mean gain is about 1°C at a 100m distance for a fixed windmill. The gain can be enhanced by up to 3°C with the addition of a burner. The cost is around €45,000 for a fixed windmill without burner. The carbon footprint is dependent on the energy of the engine. The main problem for windmills is that they do not work if the inversion layer is too high or during an advective frost. The noise can also disturb any neighbours.
• PEL-101-GV is an elicitor tested from 2004 to 2013 in Champagne. The principle is to increase the plant resistance to cold using a patented process. The efficiency depends on the phenological stage from zero before one leaf, to 0-50% after one leaf for a -2.5°C frost. The cost is about €200 per application. The carbon footprint is the same as that of any type of spray application.
• Electric heating cables have been tested in Champagne from 1992 to 2003. Experimentation with new types of cables restarted in 2017 and is still in progress. The cables are tied close to the shoots which means that in Champagne this type of protection is only possible for Guyot simple and Cordon de Royat pruning methods. The results show an efficiency of around 70 to 90% for a -4°C radiative frost which can decrease to 30% for a -8°C advective frost. The cost is between €45,000 and €100,000 per hectare, including the price of an electric generator. The main problem with this type of protection is the very important power requirement (at least 200 kW/ha). The carbon footprint is dependent on the power generation method.

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